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2023 Volume 3
Article Contents
Abstract
Introduction
Materials and methods
Materials
Preparation of mixed surimi samples
Rheological characteristics of mixed surimi samples
Apparent viscosity
Dynamic rheological behavior
Strength of mixed surimi gels
Textural properties of mixed surimi gels
Cooking loss of mixed surimi gels
Low-field nuclear magnetic resonance (LF-NMR) of mixed surimi gels
Color difference of mixed surimi gels
Scanning electron microscopy (SEM) of mixed surimi gels
Thiobarbituric acid-reactive substances (TBARS) determination
Statistical analysis
Results and discussion
Rheological properties of surimi gels
Steady-state shear properties
Dynamic elastic properties during gelation
Strength of surimi gels
Textural properties of surimi gels
Cooking loss of mixed surimi gels
Color of surimi gels
Changes in moisture distribution of surimi gels
Scanning electron microscopy of surimi gels
Thiobarbituric acid-reactive substances (TBARS) determination
Conclusions
Author contributions
Data availability
Acknowledgments
Conflict of interest
Rights and permissions
References
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ARTICLE   Open Access    

Gladiolus cut flower postharvest performance to direct breeding efforts

  • Department of Horticultural Science, University of Minnesota, 1970 Folwell Avenue, Saint Paul, MN 55108 USA

More Information
  • Gladiolus is an important floricultural and nursery crop used for gardening and floral design. The lengthy, linear stems with large, brightly colored flowers make it a long-term favorite of floral designers. Vase life ranges from 6−10+ d, making this crop a mainstay in the floral industry. The objective of this research was to test a sample of 11 advanced cut flower selections and two cultivars with varying ancestry, plant stature, and floral traits to establish a norm for future breeding and selection criteria for development of a cut flower crop ideotype. Genotypes were tested in field production trials to establish their cut stem length, visible bud date, flowering date, duration of flowering, plant height and width, number of leaves, flower petal type, flower color and petal markings. Flower stems were harvested at stage 2 and then stored at 3−5 °C. Postharvest vase solution treatments were deionized, distilled water and FloraLife Crystal Clear Flower Food 300® floral preservative for 9 d, recording 18 traits related to the inflorescence, water uptake, pH changes, dry matter, flower opening/closure, and salability. In the production trials, flowering week and plant height were the only phenotypic traits with significance. Genotypes were significantly different for nearly all traits examined whereas treatments or their interactions were less so, providing selection potential for future crop improvements. Many traits were significantly correlated, which will provide for greater efficiency and selection potential. Future research will focus on heritability of these traits to provide a foundation of knowledge to create a gladiolus cut flower crop ideotype.

  • Introduction

    Surimi gel, known as 'concentrated myofibrillar protein'[1], is a kind of gel prepared by processing fish tissue according to fixed steps, such as rinsing, dehydration, and chopping, then adding a certain number of auxiliary materials for crushing, molding, heating and cooling. Salt-soluble myofibrillar protein (mainly myosin) of surimi denatures and unfolds after heating, and then re-crosslinks and polymerizes to form large protein aggregates[2], which is the internal mechanism of forming the gel structure. To enhance the texture and taste of surimi gel products, 2%−3% salt is added to promote the formation of the protein gel network structure and enhance the solubility and functional properties of the products[3,4]. Nonetheless, numerous studies have confirmed that excessive salt intake may result in risks of disease to human health, such as hypertension, and coronary heart disease[5]. Therefore, the development of low-salt surimi products will be widely focused on in future research.

    Recently, two strategies have been innovatively proposed to improve or maintain the gel properties of low-salt surimi products: one is to use exogenous additives or sodium salt substitutes[6−8], and the other is to exploit new processing technologies[9−11]. Glutamine transaminase (TGase) is the most effective surimi quality improver to enhance the functional properties of protein, which could catalyze acyl donors in proteins (γ-Hydroxylamine group) and acyl receptors (lysine residue, primary amine compound, etc.) undergo acyl transfer reaction to form cross-linked structures[12−14]. Previous studies by Jiang et al.[15] revealed that the cross-linking effect of TGase catalysis depends on the content and spatial distribution of available substrates. In addition, lysine, as an ideal exogenous additive, has been widely used in different meat protein gel systems, which can effectively improve the gel properties of low-salt surimi gel[16] and emulsified chicken sausage[17]. Many researchers have spent a lot of time to obtain higher-quality surimi gel products through the combination of two or more exogenous additives. Many scientists devoted themselves to obtaining higher quality surimi gel products through the combination of two or more exogenous additives. For example, Cao et al.[18] demonstrated that lysine (Lys) could bring about the dissociation of actin under the condition of the presence of TGase, promoting the cooking yield and gel properties of oxidative damaged MP. Similar findings reported by Cando et al.[19] indicated that Lys could induce the changes in protein structure, which were favorable terms to heighten the cross-linking effect of TG and improve the strength of surimi gel.

    Recently, the term ε-Poly-lysine (ε-PL) was followed with interest since it's a natural amino acid polymer produced by microbial fermentation, and was speculated that it has a similar molecular structure and potential effect to Lys[20]. ε-PL, which is generally composed of 25−30 lysine residues connected by amide bonds (by ε-Amino and α-Carboxyl group), was often used as an antibacterial agent for the preservation of meat products and aquatic products[21]. Li et al.[21] explored the effect of preservative coating with ε-PL on the quality of sea bass fillets during storage. It turned out that, ε-PL treatment evidently reduced the thiobarbituric acid and volatile base nitrogen values of bass slices during storage, inhibited the growth of microorganisms, and improved the water retention, texture, and flavor characteristics of the fish. A previous study by Cai et al.[20] proved the bacteriostatic and fresh-keeping effect of the composite coating of protein and sodium alginate on Japanese sea bass, and found that the composite coating had an effect on inhibiting the proliferation of sea bass microorganisms (Escherichia coli, lactic acid bacteria, yeast, etc.), fat oxidation, protein degradation, and nucleotide decomposition. As a natural cationic polypeptide, ε-PL has the advantages of no biological toxicity and low viscosity of aqueous solution. It is noteworthy that it can produce strong electrostatic adsorption with negatively charged amino acids[22]. Its effective modification of protein helps it fully interact with gel component molecules and groups[23], which may play a role in enhancing the texture and water retention of protein gel.

    Nevertheless, few reports are based on the addition of ε-PL to explore the influence mechanism on TGase-catalyzed surimi gel properties. The current study sought to shed light on the effects of different additions of ε-PL on TGase-induced cross-linking effect and the performance of composite surimi gel, to provide a theoretical basis and reference for further research and development of 'low salt', efficient and healthy surimi products.

    Materials and methods

    Materials

    Testing materials, including marine surimi, transglutaminase (TG, enzyme activity 100 IU/g), and ε-Polylysine (ε-PL, ≥ 99% purity) were supplied by Jiangsu Yiming Biological Technology Co., Ltd (Jiangsu, China). Egg white protein was purchased from Henan Wanbang Chemical Technology Co., Ltd (Henan, China). All other chemicals were from Shanghai Yuanye Biochemical Co., Ltd (Shanghai, China) and were at least analytical grade. The ingredients of the surimi gel are shown in Table 1.

    Table 1.  Surimi samples with different treatments.
    GroupsSurimi
    (g)    		TGase
    (w/w, %)    		Egg white
    Protein
    (w/w, %)    		ε-PL
    (w/w, %)    		NaCl
    (w/w, %)
    CK300−−−0.5
    TE3000.47.0−0.5
    TE + P13000.47.00.0050.5
    TE + P23000.47.00.010.5
    TE + P33000.47.00.020.5
    TE + P43000.47.00.040.5
    TE + P53000.47.00.060.5
     | Show Table
    DownLoad: CSV

    Preparation of mixed surimi samples

    The prepared block surimi was firstly put into the chopping machine (or tissue masher) and chopped for 2 min, then different mass fractions of ingredients were added, while the chopping time was extended to 5 min (the temperature should be controlled below 10 °C during this process). The exhausted surimi paste was poured into the special mold (50 mm × 20 mm), which was heated in two stages to form the heat-induced surimi gel (40 °C water bath for 40 min; 90 °C water bath for 20 min). Above prepared surimi gel underwent an ice water bath for 30 min and finally stored overnight at 4 °C for further use.

    Rheological characteristics of mixed surimi samples

    Mixed surimi samples with different treatments were determined under a Haake Mars 60 Rheometer (Thermo Fisher Scientific, Germany) with 35 mm stainless steel parallel plates referring to the method described by Cao et al.[18], and each determination was repeated three times. After centrifugation (1,000× g, 3 min) and 4 °C, the degassed surimi sol (~2 g) was equilibrated at 4 °C for 3 min before measurement.

    Apparent viscosity

    The shear stress of the mixed surimi sol was measured at shear rates between 0−100 s−1.

    Dynamic rheological behavior

    The rheological properties of the mixed surimi sols were measured in an oscillatory mode of CD-Auto Strain at 0.02% and 0.1 Hz frequency, respectively. The heating temperature range is set to 20~90 °C while the heating rate is 1 °C·min−1.

    Strength of mixed surimi gels

    The TA-XT Plus physical property analyzer (TA-XT Plus, Stable Micro Systems Ltd, Surrey, UK) was used to analyze the mixed surimi gel strength of each group of samples (n ≥ 3) at room temperature, and the cube-shaped surimi gel samples are measured through the P/0.5 probe. Referring to the method previously described by Fang et al.[24], the test parameters are as follows, pre-test and test rate (1 mm·s−1); rate after measurement (5 mm·s−1); depressing degree (30%); trigger force (5 g); data acquisition rate (400 p/s).

    Textural properties of mixed surimi gels

    Concerning the method of Jirawat et al.[25], texture profile analysis (TPA) was employed to record the hardness, elasticity, cohesion, chewiness, and resilience of mixed surimi gels. It is well known that TPA can explore the textural properties of food through the texture analyzer (TA-XT Plus, Stable Micro Systems Ltd, Surrey, UK) equipped with a P/75 probe to simulate human oral chewing action and obtain the texture characteristic values related to human sensory evaluation. The physical property parameter settings were as follows: downforce (5 g), compression degree (50%), pre-test speed, test speed, and post-test speed (1.0 mm·s−1).

    Cooking loss of mixed surimi gels

    The cooking loss of surimi gel under different treatments was determined referring to the protocol of Dong et al.[26]. The cooked surimi gel sample was instantly absorbed dry and weighed (W5). The cooking loss (CL) is calculated as follows:

    CL(g/100g)=(M1−M2)/M1×100 (1)

    Where M1, weight of the sample before cooking; M2, weight of the sample after cooking.

    Low-field nuclear magnetic resonance (LF-NMR) of mixed surimi gels

    The LF-NMR of the mixed surimi gel was detected by a PQ001-20-025V NMR analyzer (Niumag Analytical Instruments Co., Ltd, Suzhou, China) referring to the previous method conducted by Li et al.[27]. Relevant characteristic parameters were set as follows: sampling frequency (200 KHZ), echo time (0.3 ms), and cumulative number (8). Keeping the surimi gel sample (approximately 2 g) at room temperature for 30 min, they were carefully put into a cylindrical nuclear magnetic tube (15 mm in diameter), and finally, the relaxation time (T2) was recorded using the Carr Purcell Meiboom Gill (CPMG) pulse sequence.

    Color difference of mixed surimi gels

    CM-5 colorimeter (Konica Minolta Sensing, Inc., Tokyo, Japan) was used for surimi gel with different treatments following to the procedure of Wang et al.[28]. Several 1 cm thick slices were cut from surimi samples (n = 3) selected from different treatment groups, and the gel whiteness was calculated according to the following formula:

    Whiteness=100−√(100−L∗)2+a∗2+b∗2 (2)

    Scanning electron microscopy (SEM) of mixed surimi gels

    According to the previously described procedure by Gao et al.[29], the square-shaped surimi gels (4 mm × 4 mm × 4 mm) were immersed in 0.1 mol·L−1 phosphate buffer (pH 7.2) containing 2.5% (v/v) glutaraldehyde for 24 h. The above samples were washed using phosphate buffer (0.1 mol·L−1, pH 7.2) three times and then subsequently dehydrated in a series of alcohol solutions. The microstructures of the mixed surimi gels were imaged using an FEI Verios 460 SEM (FEI Inc., Hillsboro, OR, USA).

    Thiobarbituric acid-reactive substances (TBARS) determination

    The TBARS value was analyzed by the method described by Hu et al.[30] with slight modification. Thiobarbituric acid solution (1.5 mL) and 8.5 mL of trichloroacetic acid solution were added to the sample in turn, the mixture was bathed in water at 100 °C for 30 min. The supernatant was extracted and centrifuged twice (3,000× g, 5 min): (1) The original supernatant (5 mL) was taken and the same amount of chloroform for mixed centrifugation; (2) The second supernatant (3 mL) and petroleum ether (1.5 mL) were taken for mixed centrifugation. Finally, a small amount of lower liquid was taken to determine the absorbance (A532 nm). The final result was expressed in malondialdehyde equivalent (mg·kg−1).

    Statistical analysis

    All statistical analyses of data were investigated by statistical product and service solutions IBM SPSS Statistics version 23.0 (IBM SPSS Inc., Chicago, USA). The LSD all-pairwise multiple comparison method was used for the least significance analysis, and p < 0.05 was considered to indicate significance. The experimental data are expressed as mean ± standard deviation (SD) and plotted using Origin 2019 (Origin Lab, Northampton, MA, USA) software.

    Results and discussion

    Rheological properties of surimi gels

    Steady-state shear properties

    The steady-state shear flow curve can be used to characterize the interaction between proteins. The steady shear flow changes of apparent viscosity (Pa·s) of composite surimi with shear rate (s−1) under different treatments are shown in Fig. 1a. The apparent viscosity of all samples decreased significantly (p < 0.05) with increasing shear rate, exhibiting shear-thinning behavior[31]. In the range of shear rates from 0.1 to 100 s−1, the samples with TGase addition were always higher than the control, indicating that the induction of TGase enhanced the cross-linking of surimi proteins and formed a more stable structure. The surimi samples added with a lower proportion of ε-PL (0.005% and 0.01%) were regarded as lower viscosity fluid (Fig. 1a). The possible reason was that the low concentration of ε-PL provided a weak effect on the pH value of the surimi system. As a consequence, the content of the net charge provided was relatively small and the electrostatic interaction between the surimi proteins was weakened[20].

    Figure 1.  Effect of different treatments on rheological properties of surimi.
    DownLoad: Full-Size Img PowerPoint
    Dynamic elastic properties during gelation

    The elastic modulus (G′) mainly depends on the interaction between protein molecules, which can reflect the change of elasticity in the heat-induced surimi gel. As shown in Fig. 1b, the gel process of surimi in the control group was a thermodynamic process consisting of two typical stages. In the first stage, the value of G' showed a gradual downward trend in the range of 20~50 °C. This is mainly because, (1) the activity of endogenous protease in surimi is increased; (2) the myosin light chain subunits of surimi are dissociated under the action of protease, forming myosin and actin[24]; (3) heat-induced hydrogen bonds break between protein molecules, thus enhancing the fluidity of the gel system[31]. The second stage: From 50 to 73 °C, the G' value increases rapidly. As the temperature continues to rise to 90 °C, the G 'value keeps rising steadily. At this time, the gel network structure gradually became stable and irreversible.

    Compared with several curves in Fig. 1b, TGase treatment could significantly increase the G' value. The change trend of G' value of the samples added with TGase and ε-PL were similar to that of the control group, but the former increased faster and the maximum value of G' was also significantly higher. The temperature corresponding to the first peak of G' gradually decreased (PL1≈PL2 < PL4≈TE < PL3≈PL5 < CK), indicating that the process of protein denaturation and aggregation was advanced. This result showed that the proper amount of ε-PL (0.04%) in combination with TGase can reduce the thermal denaturation temperature of protein-forming gel and improve the forming ability of composite gel, which was unanimous with the changes in texture and properties of surimi gel (Table 2). Furthermore, the addition of a small amount (0.005%) or an excessive amount (0.06%) of ε-PL made the mixed surimi protein system more unstable, affecting the ability of TG-induced gel formation as the last resort[32].

    Table 2.  Effect of different treatments on the textural properties of surimi gels.
    GroupsHardness (g)SpringinessCohesivenessChewiness (g)Resilience
    CK811.40 ± 45.28de0.81 ± 0.01a0.53 ± 0.02b498.36 ± 21.58c0.21 ± 0.01e
    TE1105.80 ± 61.83c0.83 ± 0.01a0.56 ± 0.01b510.40 ± 26.04c0.24 ± 0.00bcd
    TE + P1736.01 ± 18.49e0.80 ± 0.03a0.61 ± 0.00a348.78 ± 18.36d0.23 ± 0.01cde
    TE + P2777.45 ± 39.61de0.80 ± 0.01a0.60 ± 0.02a307.03 ± 12.97e0.22 ± 0.00de
    TE + P3869.66 ± 45.82d0.83 ± 0.02a0.63 ± 0.01a485.06 ± 22.73c0.28 ± 0.00a
    TE + P41492.80 ± 77.13a0.83 ± 0.01a0.60 ± 0.01a721.74 ± 31.55a0.26 ± 0.01ab
    TE + P51314.60 ± 84.10b0.81 ± 0.00a0.60 ± 0.02a652.36 ± 30.24b0.25 ± 0.01bc
    Different lowercase letters in the same column indicated significant differences (p < 0.05).
     | Show Table
    DownLoad: CSV

    Strength of surimi gels

    Gel strength is one of the vital indicators to test the quality of surimi products, which directly affects the texture characteristics and sensory acceptance of the products. The strength of mixed surimi gel with TGase was significantly enhanced by 23.97% (p < 0.05) compared with the control group after heat-inducing. This enhancement is probably caused by the crosslinking promotion of TGase (Fig. 2a). A deeper explanation is that under the catalysis of TGase, the ε-amino group on lysine and the γ-amide group on glutamic acid residues undergo acylation reaction inside or between proteins, forming ε-(γ-Glutamyl)-lysine covalent cross-linking bond which promotes the production of the protein gel network[26].

    Figure 2.  (a) Catalytic reaction of glutamine transaminase and (b) effect of different treatments on gel strength and cooking loss of surimi gel. a−d/A−D: values with different lowercase letters indicate significant difference (p < 0.05).
    DownLoad: Full-Size Img PowerPoint

    On the basis of adding TGase, the strength of the mixed gel with ε-PL concentration ranging from 0.005% to 0.03% was lower than that of TE (Fig. 2b). It was speculated that the surimi sample with low concentration ε-PL was a fluid with lower viscosity, and the interaction between protein and water is strengthened, while the electrostatic interaction between proteins is further weakened[33]. This was also consistent with the change in rheological properties in Fig. 1a. Nevertheless, with the increase of ε-PL content to 0.04%, the gel strength of surimi gel significantly increased and reached the highest value (781.63 g·cm), which was about 21.03% higher than that of the TE group (p < 0.05) (Fig. 2b). The increase of gel strength in this process was obtained due to the following three possible reasons, (1) ε-PL is a cationic amino acid with positive charge, which can improve the pH value of protein or meat product system; (2) The interaction between the ε-amino group of ε-PL and the aromatic residue of protein, namely the cation-π interaction, can change the structure of meat protein[34]; (3) Protein (mixed surimi system) with high ε-amino group content, TGase has strong gel improving ability[35].

    Such synergy (ε-PL = 0.04%), as a comprehensive result of different impactors, is that after the surimi was mixed under the optimal ratio conditions, the synthesis of TGase enzyme catalysis, pH value shift, changes in protein and amino acid composition, etc., increased the strength of various forces, thus forming a denser stereoscopic network structure. Note that when the content of ε-PL reached 0.06%, the gel strength of the corresponding surimi gel decreased by 10% compared with 0.04%. Similarly, others reported the result that alkaline amino acids led to the reduction of the strength of the myosin gel of bighead carp[36].

    Textural properties of surimi gels

    TPA, also known as whole texture, is a comprehensive parameter that determines the sensory quality of surimi gel, including hardness, elasticity, cohesion, chewiness, and resilience[37]. As shown in Table 2, the addition of TGase significantly improved the texture properties of surimi gel (p < 0.05), which is related to TGase's ability to induce surimi protein to form more ε-(γ-Glu)-Lys covalent bond during heating[38] (Fig. 2a). Compared with the cross-linking induced by TGase alone, the gel hardness of the mixed surimi gel treated with ε-PL showed a similar change to the gel strength (Fig. 2b). As the concentration of ε-PL increased from 0.005% to 0.04%, the hardness of surimi gel gradually increased until it reached the maximum (1,492.80 g). At the same time, we also observed that the elasticity, cohesion, and chewiness of the composite gel reached the highest values with the 0.04% ε-PL, and these were higher than those of the TGase-only group. Similar to the findings of Ali et al.[39], the author found that the combination of ε-PL and beetroot extract can effectively replace nitrite, which produced a marked effect in maintaining the color of Frankfurt sausage and improving the texture and performance. However, the data we collated above (Table 2) also showed a clear phenomenon, that is, the addition of ε-PL with lower concentration (0.005%−0.02%) or highest concentration (0.06%) was not conducive to the combination with TGase to improve the texture characteristics of mixed surimi gel.

    Cooking loss of mixed surimi gels

    Cooking loss indicates the water holding capacity of heated surimi, which usually represents the stability of the three-dimensional network structure of surimi gel[40]. The 0.4% TGase significantly reduced the cooking loss of surimi samples (p < 0.05), which was 4.91% lower than that of the control group (Fig. 2b). When the addition of PL (combined with TGase) gradually increased from 0.005% to 0.04%, the cooking loss of surimi showed a decreasing trend and reached the minimum at 0.04%. The ε-PL-added surimi gel samples had higher cooking loss compared with that of only with TGase. Most notably, this may be due to ε-PL is able to further exert the cross-linking effect of TGase. A similar finding was reported in the study by Ma et al.[22], adding ε-PL is able to improve the solubility of myofibrillar proteins. Proteins with high solubility are more easily induced by TGase during heating, which aggravates the cross-linking between ε-PL-protein or protein-protein and forms a disordered gel network structure with relatively weaker water-holding capacity.

    Color of surimi gels

    As shown in Table 3, the high lightness (L*), low yellowness (b*), and high whiteness of surimi in the control group were relatively low, with values of 72.49, 10.42, and 70.56 respectively. After TGase was added to induce cross-linking, these values increased significantly (p < 0.05), which may be related to the photochromic effect of water molecules released from gel matrix under TGase-induced surimi protein cross-linking reported in the previous study[41]. Furthermore, on the basis of adding TGase, it was interesting to see that the L* and whiteness values of surimi gel first increased and then gradually decreased with the increase in ε-PL concentration. The influence of ε-PL combined with TGase on the whiteness of gel can be attributed to three reasons: (1) The addition of ε-PL can effectively increase the substrate content of TGase, and promote the cross-linking between proteins, so as to obtain a much more compact surimi gel structure, which affects the refractive index of light; (2) The water retention performance of the high surimi gel was significantly improved with the addition of ε-PL[42] (Fig. 2b), at this time, the L* value (positively related to the whiteness) value showed a decreasing trend with the decrease of the surface free water content of the gel sample; (3) With the increase of ε-PL concentration, some colored substances, formed due to the accelerated Maillard reaction rate during the preparation of gel, may have an adverse effect on the improvement of gel whiteness[43]. After adding TGase to induce cross-linking, although the whiteness value of composite surimi was significantly enhanced, ε-PL was not enough to further improve the whiteness value of final mixed surimi gel, and high concentration so far as to have a negative impact on the whiteness value.

    Table 3.  Effect of different treatments on the color of surimi gels.
    GroupsL*a*b*Whiteness
    CK72.49 ± 0.82e−0.92 ± 0.01e10.42 ± 0.33d70.56 ± 0.65d
    TE77.82 ± 0.34ab−0.23 ± 0.02c12.29 ± 0.29bc74.64 ± 0.26ab
    TE + P178.39 ± 0.40a−0.14 ± 0.01a12.46 ± 0.12ab75.05 ± 0.41a
    TE + P278.42 ± 0.43a−0.17 ± 0.0b12.46 ± 0.15ab75.07 ± 0.32a
    TE + P377.48 ± 0.16b−0.18 ± 0.02b12.37 ± 0.09abc74.31 ± 0.11b
    TE + P476.34 ± 0.05c−0.22 ± 0.01c12.73 ± 0.02a73.13 ± 0.04c
    TE + P575.48 ± 0.18d−0.26 ± 0.01d12.01 ± 0.14c72.70 ± 0.19c
    Different lowercase letters in the same column indicated significant differences (p < 0.05).
     | Show Table
    DownLoad: CSV

    Changes in moisture distribution of surimi gels

    The water distribution in surimi gel products was measured by LF-NMR[44], and the results were inverted to obtain the transverse relaxation time (T2), which reflects the strength of water fluidity[45]. There are four fitted wave peaks which are assigned to four different water distribution states and wave peak ranges (Fig. 3, Table 4): strong bound water T21 (0.1−1 ms), weak bound water T22 (1−10 ms), non-flowing water T23 (10−100 ms) and free water T24 (100−1,000 ms)[46]. At the same time, similar characteristics (the main peak is centered on T23) are possessed by the water distribution of all surimi gel samples. The addition of TGase increased the proportion of non-flowing water, accompanying the significant decrease in the content of free water (p < 0.05), compared with the control group. It proved that the addition of TGase brought this phenomenon, namely the bound water in surimi gel was partially transferred to the non-flowing, which also indicated the reduction of cooking loss of surimi samples induced by TGase (Fig. 2). On the basis of adding TGase, the low level of ε-PL (0.005%, 0.01% and 0.02%) inhibited the transition of free water in surimi gel to non-flowing water, in which the proportion of T23 decreased by 2.05%, 2.74%, and 1.42% respectively compared with the surimi gel only with TGase, while T24 increased by 15.76%, 14.17%, and 4.43% respectively. The proportion of P23 in the surimi gel sample (ε-PL = 0.04%) was equivalent to that of the TE group, implying that the addition of appropriate ε-PL was not directly connected with the changes in water distribution in surimi after TGase-induced cross-linking, and slight addition would have a negative impact, which was unanimous with the above research results of cooking loss (Fig. 2a).

    Figure 3.  Effect of different treatments on the transverse relaxation time T2 of surimi gel.
    DownLoad: Full-Size Img PowerPoint
    Table 4.  Effect of different treatments on the transverse relaxation time T2 of surimi gel.
    GroupsP21 (%)P22 (%)P23 (%)P24 (%)
    CK2.175 ± 0.186c1.198 ± 0.012e82.863 ± 0.691bc13.764 ± 0.091a
    TE1.938 ± 0.095d2.166 ± 0.043a85.144 ± 1.336a10.752 ± 0.033e
    TE + P12.705 ± 0.067b1.414 ± 0.009d83.435 ± 1.616b12.446 ± 0.105c
    TE + P23.005 ± 0.003a1.845 ± 0.056b82.874 ± 1.739bc12.276 ± 0.108c
    TE + P33.107 ± 0.063a1.715 ± 0.033c83.950 ± 1.587ab11.228 ± 0.086d
    TE + P41.770 ± 0.018d2.099 ± 0.059a85.021 ± 1.756a11.110 ± 0.144d
    TE + P53.121 ± 0.007a1.758 ± 0.107bc82.136 ± 1.091c12.985 ± 0.018b
    Different lowercase letters in the same column indicated significant differences (p < 0.05).
     | Show Table
    DownLoad: CSV

    Scanning electron microscopy of surimi gels

    The effect of different treatment methods on the microstructure of surimi gel was observed by SEM. As shown in Fig. 4, the microstructure of the control surimi gel (Fig. 4a) was observed to be enormously loose, uneven, and irregular, with large pores, which explained the reason why the control surimi gel had low strength and large cooking loss (Fig. 2b). In addition, the morphological properties of another group of surimi gel (TGase-induced) are appreciably different from the scanning electron micrograph mentioned above (Fig. 4b). Numerous compact and evenly distributed small pores were observed, instead of the loose structure in the control sample, which accounted for the fact that TGase could interact with proteins to form a more uniform and orderly three-dimensional network structure in the process of gel formation[47]. Moreover, similar findings were also reported in the previous studies of Dong et al.[26]. When treated with TGase and ε-PL (from 0.05% to 0.04%), the surface of the surimi gel sample gradually became flat through observation (Fig. 4f). We found that some smaller pores were formed and some larger pores were slightly supplemented visually. Remarkably, when the addition of ε-PL increased to 0.06% (Fig. 4g), the structure of surimi gel was not as uniform as before, and some large and irregular holes appeared obviously. This phenomenon might be related to moderate ε-PL, especially 0.02%, which can promote the cross-linking of TGase with protein and the aggregation/denaturation of different components, which agreed with the change of coagulation strength of surimi samples.

    Figure 4.  Effect of different treatments on the microstructure of surimi.
    DownLoad: Full-Size Img PowerPoint

    Thiobarbituric acid-reactive substances (TBARS) determination

    TBARS value, which can reflect the degree of lipid oxidation and rancidity of surimi, is an important indicator for the occurrence of oxidation[48]. Some substances in surimi, such as unsaturated fatty acids, will inevitably undergo oxidative decomposition to produce a large amount of malondialdehyde (MDA), the latter reacts easily with thiobarbituric acid (TBA) reagent to produce red compounds with maximum absorbance at 532 nm. As illustrated in Fig. 5, when TGase and a certain amount of PL (from 0.005% to 0.06%) were added, the TBARs value of surimi gels decreased to 2.03 and 1.67 mg/kg respectively, compared with the control group (2.26 mg/kg). This shows that the addition of both can significantly reduce the TBARS value of surimi gel (p < 0.05), considered to be a cue for the fat oxidation of surimi being inhibited. In addition, we also found that the antioxidant effect of PL was dose-dependent. The ε-PL can be chelated by ferrous ions along with the ability to scavenge free radicals like hydroxyl radicals, ensuring its antioxidant properties[33]. The ε-PL was prospectively considered as an antioxidant additive to prevent surimi protein from deteriorating induced by oxidation[49]. Similarly, making use of lysine or ε-PL as antioxidants in plant protein and meat protein has been widely reported[33, 50]. Fan et al.[42] confirmed that ε-PL addition has a significant effect on maintaining a high total phenolic content and vitamin C levels in fresh lettuce, which also shows that it has certain antioxidant activity.

    Figure 5.  Effect of different treatments on TBARS values of surimi gel. a−f: values with different lowercase letters indicate significant difference (p < 0.05).
    DownLoad: Full-Size Img PowerPoint

    Conclusions

    The addition of ε-PL at different concentrations had an apparent impact on the characteristics of TGase-induced mixed surimi gel, accompanied by the following situations: The 0.04% ε-PL provided a synergistic effect to promote the aggregation and crosslinking of surimi proteins induced by TGase; The rheology, LF-NMR and SEM results showed that the appropriate concentration (0.04%) of ε-PL apparently enhanced the initial apparent viscosity and elasticity of surimi samples, which was conducive to the formation of a more dense and uniform three-dimensional network structure, further limiting the flow of water in surimi and the exudation of hydrophilic substances; Simultaneously, the network strength was strengthened along with the texture properties of the mixed surimi gel. Furthermore, ε-PL had a strong ability to inhibit lipid oxidation in mixed surimi gel, showing a concentration dependence. When the content of ε-PL ran to lowest (0.005%−0.01%) or highest (0.6%), the improvement of the quality of surimi mixed gel was opposite to the above. The results show that ε-PL can be perceived as a prospective polyfunctional food additive to improve the texture properties, nutritional advantages, and product stability of surimi products.

  • The authors confirm contribution to the paper as follows: study conception and design: Cao Y, Xiong YL, Yuan F, Liang G; data collection: Liang G, Cao Y, Li Z, Liu M; analysis and interpretation of results: Li Z, Cao Y, Liang G, Liu Z, Liu M; draft manuscript preparation: Li Z, Cao Y, Liu ZL. All authors reviewed the results and approved the final version of the manuscript.

  • The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

    • Acknowledgments

    This work was financially supported by the Natural Science Basic Research Program of Shaanxi (No. 2023-JC-YB-146), the fund of Cultivation Project of Double First-Class Disciplines of Food Science and Engineering, Beijing Technology & Business University (No. BTBUKF202215), the Innovation Capability Support Plan of Shaanxi (No. 2023WGZJ-YB-27), the Agricultural Technology Research and Development Project of Xi'an Science and Technology Bureau (No. 22NYYF057), and Jiangsu Yiming Biological Technology Co., Ltd. in China.

  • The authors declare that they have no conflict of interest.

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  • Cite this article

    Anderson NO. 2023. Gladiolus cut flower postharvest performance to direct breeding efforts. Technology in Horticulture 3:21 doi: 10.48130/TIH-2023-0021
    Anderson NO. 2023. Gladiolus cut flower postharvest performance to direct breeding efforts. Technology in Horticulture 3:21 doi: 10.48130/TIH-2023-0021
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Gladiolus cut flower postharvest performance to direct breeding efforts

  • Department of Horticultural Science, University of Minnesota, 1970 Folwell Avenue, Saint Paul, MN 55108 USA

  • Received: 30 June 2023
  • Accepted: 09 August 2023
  • Published online: 02 November 2023
Technology in Horticulture  3,  Article number: 21  (2023)  |  Cite this article

Abstract: Gladiolus is an important floricultural and nursery crop used for gardening and floral design. The lengthy, linear stems with large, brightly colored flowers make it a long-term favorite of floral designers. Vase life ranges from 6−10+ d, making this crop a mainstay in the floral industry. The objective of this research was to test a sample of 11 advanced cut flower selections and two cultivars with varying ancestry, plant stature, and floral traits to establish a norm for future breeding and selection criteria for development of a cut flower crop ideotype. Genotypes were tested in field production trials to establish their cut stem length, visible bud date, flowering date, duration of flowering, plant height and width, number of leaves, flower petal type, flower color and petal markings. Flower stems were harvested at stage 2 and then stored at 3−5 °C. Postharvest vase solution treatments were deionized, distilled water and FloraLife Crystal Clear Flower Food 300® floral preservative for 9 d, recording 18 traits related to the inflorescence, water uptake, pH changes, dry matter, flower opening/closure, and salability. In the production trials, flowering week and plant height were the only phenotypic traits with significance. Genotypes were significantly different for nearly all traits examined whereas treatments or their interactions were less so, providing selection potential for future crop improvements. Many traits were significantly correlated, which will provide for greater efficiency and selection potential. Future research will focus on heritability of these traits to provide a foundation of knowledge to create a gladiolus cut flower crop ideotype.

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    Introduction

    • South Africa is the center of origin and diversity of gladiolus or sword lily, Gladiolus × hybridus Rodigas (Iridaceae), although species are also native in the Mediterranean (Italy, the Arabian Peninsula) and into the Russian Federation[1]. It is a major cut flower in the floriculture industry (ranked in the top ten cut flower crops), used as a line flower in line-mass designs[2] and sold in mixed or single cultivar bunches at retail farmer's markets or wholesale commercial floral markets, respectively. Gladiolus have been in the top ten cut flowers in Dutch auctions since 1958, with ~1 M gladioli stems/year sold[3]. In 2018, gladiolus corm production in the Netherlands was 637 ha and floral spike production 153 ha[4]. In 2020, the US value of cut flower gladiolus was US$14.83M (w, wholesale farmgate value)[5], while Chinese production of gladiolus is increasing[6]. In China, gladiolus production covered 3,300 ha in 2014 which made it the second-most grown geophyte in China after Lilium[7]. It is also grown as an ornamental garden plant (non-hardy, tender perennial in northern latitudes, USDA Z3-4)[8].

      Gladiolus species are geophytic with corms (compressed stems) for underground storage organs[9]. In commercial production, gladioli are planted as 3−5 year-old corms, capable of flowering[10,11]. Gladioli are vegetatively propagated via daughter corms and/or cormels in commercial production. Daughter corms arise above the current season's mother corm; all corms and cormels arise from the daughter corm's basal plate and consist of an enlarged stem axis with nodes and internodes with dry, scale-like leaves forming a protective 'tunic'[12]. Thus, gladiolus have tunicate corms. Classically, one daughter corm is generated/year by the mother corm but cormel numbers vary from one to hundreds/corm, depending on the cultivar[12]. Cormels differ from daughter corms, being smaller and arising directly from the basal plate[12]). After corm/cormel sprouting, each propagule produces adventitious and contractile roots, the latter of which are thick fleshy roots which pull the seedling or corm deeper into the ground[13]. Seedlings form both root types and a small corm within 1−4 weeks post-germination immediately pulls the corm below the soil surface (N. Anderson & R. Eperjesi, 2019, unpublished data).

      Gladiolus production is for either cut flower (floral design) purposes or for use as a garden annual/perennial[14], depending on the USDA Hardiness Zone since most are frost- and cold-sensitive in northern latitudes[8]. The floral spike (defined as the central stem with all individual florets)[1] is cut when petal coloration starts in the lowest floret but before it reaches anthesis[15], commercially referred to as Stage 2[11,16]. The florets open acropetally or from the base upwards in a linear fashion over time, 1x/day[10]. All commercial cut flower and garden cultivars are non-fragrant, although ten or more wild species have fragrance, including G. orchidiflorus (Anderson, 1999, unpublished data), G. tristis and G. recurvus[17].

      Gladiolus stems are bunched in 5, 7 or 10 stems/bunch[16]. There are four grades (1−4) for minimum stem length 80−115 cm), minimum flower diameter (6.25−8.75 cm), stem strength (15°), stem deviation curvature from vertical (5−10 cm), and the minimum number of flowers or florets / stem (6−12)[10,11,16]. The four major flower color classes of gladiolus are blue, yellow, red, and green although whites are commonly produced as well as novelty types with varying petal shapes, ruffled edges, etc.[16]. Gladiolus floral spikes can be stored dry or in floral preservative at 3−4 °C, 90% relative humidity for 2 to 3 weeks[10,16] At room temperature (20−22 °C), expected vase life is 7 d minimum. Gladiolus may have ethylene (C2H4) sensitivity during postharvest storage[16,18] necessitating treatment with either silver thiosulfate (STS) or 1-Methylcyclopropene (1-MCP)[19−21]. Ethylene response may reduce flower life by aborting unopened flower buds[21]. Prevention of ethylene buildup likewise increases postharvest longevity of gladiolus[18]. Gladiolus stem tips are negatively geotropic and are predominantly shipped/stored upright to prevent stem tip bending away from gravity[21].

      Without floral preservatives, gladiolus may have shortened postharvest life due to lack of water from occlusions of basal stem cuts and microbial plugging of the xylem[2, 10,19]. Sucrose (20%; overnight)[21,22] or cobalt[23] pulsing, as well as floral preservatives increase vase life of flower spikes as high as 12.3 d, although the range in vase life of a stem is 6−10 d[21]. Previous gladiolus cut flower postharvest research reported that higher temperatures during production decreased cut stem fresh weights, but the opposite was found with higher CO2 levels[24].

      Gladiolus breeding is primarily accomplished by amateur breeders in gladiolus societies, e.g. the North American Gladiolus Council[11], one private sector company (Breck's Holland)[25] and one public sector breeding program (University of Minnesota, USA)[8,26−28]. Many new cultivars are released each year using divergent ancestries[11,29]. In recent decades, significant corm production, postharvest and physiological research on gladiolus has been conducted in Brazil (Universidade Federal de Santa Maria, Santa Maria), Pakistan (The University of Agriculture, Faisalabad and Peshawar), India (Indian Agriculture Research Institute, New Delhi; University of Agricultural Science, Bangalore), Egypt (Kafrelsheikh University, Kafr El-Sheikh; Agricultural Research Center, Giza), Poland (University of Agriculture, Kraków), the Czech Republic (Mendelova zemědělská a lesnická univerzita v Brně, Brno) and Italy (Universita degli Studi di Bari, Bari). However, much of the production and postharvest techniques to achieve saleable product aren't translated into public or private sector breeding programs to aid in the advancement of the crop. To unite physiological and breeding/genetic research efforts, the University of Minnesota flower breeding program is developing cut flower cultivars with unique floral colors and patterns, along with cold tolerance for USDA Z3-4[8], rapid generation cycling (RGC)[21], dwarf types for potted plant and container production, and vegetative or seed-propagated F1 hybrids. Most would be new traits for this crop and provide unique opportunities for postharvest testing to aid in breeding and selection. Thus, the objective of this research was to test a sample of advanced cut flower selections within the breeding program with varying ancestry, plant stature, and floral traits to establish baseline data for future breeding and selection for development of a gladiolus cut flower crop ideotype.

    Materials and methods

    • This study was conducted at the public sector University of Minnesota Gladiolus Breeding & Genetics Program, involving greenhouse, laboratory, and field facilities in Saint Paul and Rosemount, Minnesota, USA.

      Genotypes

    • Thirteen cut flower gladiolus genotypes were tested in this experiment. Eleven clonal genotypes (numbered selections, GL-1 to GL-11; Table 1) were hybrids or inbreds derived from the University of Minnesota breeding program plus two commercial named comparisons ('Beatrice', 'Manhattan'). Genotypes GL-1 to GL-11 were hybrids or inbreds produced from controlled crossings or selfs, respectively, in the St. Paul campus greenhouses (44°59'17.8" N lat., −93°10'51.6" W long.) during 2006−2016 or as open-pollinated (OP) seedlings in field trials. The OP seedlings were most likely inbreds, due to self compatibility operating in tetraploid gladioli. Seedling growouts to flowering (1−5 years) for subsequent clonal evaluation occurred in breeder field trials, Rosemount, MN (44°42'58.2'' N, −93°5'54.9" W)[27,28]. The short stature genotypes did not require staking or additional support in the field production (Fig. 1) whereas the taller ones did if the stems were left to completely flower (Fig. 2).

      Table 1.  Hybrid gladioli of dwarf (< 90 cm) or tall stature (> 90 cm; Breck's Holland[25]) tested for field performance data (wk 22 planting dates), averaged over three years (2019, 2021, and 2022) grown under standard commercial field production trials in Rosemount, MN, USA for: number of weeks to visible bud date (VBD; VBD wk. no. – planting wk. no.), number of weeks to flowering (flowering wk. no. – planting wk. no.), number of weeks to termination of flowering (termination wk. no. – planting wk. no.), plant height (cm), plant width (cm), number of leaves, and flower petal type, flower color or petal markings.

      GenotypeNo. wks
      to VBD      		No. wks to flowering, terminationPlant height
      (cm)      		Plant width
      (cm)      		No. of
      leaves      		Flower petal type, flower color or petal markings
      Dwarf stature (< 90 cm)
      GL-11013 ab, 1580.0 b23.08Slightly ruffled, peach, white venation
      GL-21215 b, 1957.0 a13.09Hooded lt. pink/creamy white, yellow throat
      Tall stature (> 90 cm)
      GL-31213 ab, 1591.5c44.06Ruffled red w/white throat
      GL-41012 a, 1698.0 c20.56Fuchsia-red w/white streaked venation
      GL-51112 a, 14101.0 cd26.56Dark orange
      GL-61113 ab, 16115.0 d36.08Hooded cream w/yellow throat, red venation
      GL-71113 ab, 14111.0 d228Red
      GL-81112 a, 1693.0 c25.08Ruffled, red w/white throat
      GL-91012 a, 14112.0 d60.08Ruffled red w/yellow throat
      GL-101014 ab, 16117.2 de16.58Ruffled peach w/blotch (eye)
      GL-111214 ab, 16121.0 de53.08Ruffled orange w/white throat
      'Beatrice'1113 ab, 17104.5 cd27.68Ruffled pink picotee, white w/yellow throat
      'Manhattan'1012 a, 17100.5 cd43.58Red
      Significance0.782 ns0.034 *, 0.195 ns0.001 ***0.158 ns0.166 ns
      Flowering termination week number was determined when > 50% of the flowers had senesced. Significance (p-values) were determined from univariate ANOVAs and mean separations derived from Tukey's Honestly Significantly Difference (HSD) test at α = 0.05.

      Figure 1. 

      Production field planting with an example nonlodging gladiolus genotype (GL-1). Scale: bar = 6 cm.

      Figure 2. 

      Gladiolus cut flower stem lodging in the field production trials (GL-4), requiring staking or use of support mechanisms. Scale: bar = 6 cm.

      Field production experiments

    • Prior to the present study, these genotypes were tested for field performance data for three years (2019, 2021, and 2022) when grown under standard commercial field production trials; planting occurred during wk 22 (starting wk number). The tested genotypes were phenotypically categorized by stem length of either dwarf (< 90 cm) or tall statures (> 90 cm)[25] as well as for important production and postharvest traits, including visible bud date (VBD) week number, flowering week number, termination (of flowering) week number, plant height (cm), plant width (cm), number of leaves, flower petal type, flower color and petal markings (Table 1). Flowering termination week number was determined when > 50% of the flowers/stem had senesced.

      In 2022, 3- to 5-year-old mature (capable of flowering) corms of the 13 selected genotypes for postharvest testing were grown in the fields. Corms were in the size grade ranges of 2.5 cm (Number 3) to 3.8 cm (Number 1), which ensured that all were capable of flowering[30]. As many as n = 30−100 clonal ramets of each genotype were grown for evaluation.

      Cultural conditions for the cut flower gladiolus trial were similar to those used for other herbaceous annuals and perennials in the University of Minnesota breeder field[31], located at the University of Minnesota Rosemount Research and Outreach Center, Rosemount, MN, USA. In week 22 (29 May 2022), the n = 30−100 clonal ramets (corms) per accession were planted in spaced rows (7.6 cm on center or On Center (O.C.) within rows; 61.0 cm among rows) in a trenched system, completely randomized design. Corm depth burial was 7.6−10.2 cm, as per recommendations[30]. Field plots were fertilized with urea (56 kg/ha actual N, preplant granular) with hand weeding, mechanical tilling, and pre-emergent herbicide chemical applications for weed control (Fortress®, Isoxaben + Dithiopyr granular; 22.7 kg/0.4 ha; Amvac Chemical Corp., Bluffton, SC, USA). Overhead boom irrigation was used to supplement intermittent rainfall to ensure average precipitation of 2.54 cm/wk.

      Postharvest experiment

    • Cut flower harvest occurred during wk 37 (2022), once all of the genotypes were at flowering stage with sufficient numbers of stems available for the postharvest study. Harvest was at Stage 2, when color was showing in the petals of the lower flowers[10,16]. Stems were cut in early morning (0700−0800 HRS), with 1/3 of the lower leaves were removed, followed by placement directly into standard 25 cm cooler buckets with deionized water. One genotype was placed in each cooler bucket (38.1 cm × 18 cm or 15" × 8"; www.koehlerdramm.com/pr/COOLER-BUCKET-15-X-8-BLACK/42576); once sufficient stems were harvested, the floral buckets were placed into shade for transport to the St. Paul campus once all the harvesting had occurred. Stems were immediately stored in a dark, walk-in cooler (3−5 °C) until the postharvest experiment began in < 24 h.

      Unlike previous studies where the stems were recut to the standard 75 cm length[19,32], the inclusion of dwarf stature (< 90 cm) types necessitated using different stem lengths (Fig. 3). Thus, each stem was recut (2 cm removed) prior to the start of the postharvest experiment[24].

      Figure 3. 

      Example cut tall (left) vs dwarf (right) glad stem lengths. Scale: bar = 14 cm.

      The postharvest experiment was conducted during wks 37−38 (2022) in the laboratory at standard conditions of 24 h continuous light (10 µmol·sec−1·m−2) at 21 °C. Two solution treatments were tested: tested with two treatment solutions deionized, distilled water (DDW) and Floral Life floral preservative (FLFP; FloraLife Crystal Clear Flower Food 300® floral preservative; https://shop.floralife.com/) applied as continuous vase solutions. There were n = 6 (< 6 in some genotypes) replications/treatment solution/genotype, making a total of 13 genotypes × 2 treatments × 6 replications = 156 experimental units. Due to the size of the stems, large pedestal vases were used (24.765 cm, Syndicate Sales; https://directfloral.com/syndicate-sales-975-pedestal-vase-fiesta-assortment) and filled with 1.5 L of solution/vase. Vases were arranged in a completely randomized design (CRD) on the lab bench for the duration of the experiment; the experiment was conducted for 9 d.

      Data collection

    • During the course of the experiment, the following parameters were measured, either at the beginning, ending or during the experiment: inflorescence cut stem length (cm), total no. of floret buds/stem, inflorescence internode length (cm), total no. (%) opened flowers, day 0 stem fresh weight (FW; g), day 9 stem FW (g), ΔFW (g; day 9 FW – day 0 FW), day 9 dry weight (DW; g), % water, 1st flower diameter (cm), 3rd flower diameter (cm), beginning and final pH, ΔpH, solution volume used per stem (ml), number of flowers senesced/day in days 1–9, total number of flowers senesced in days 1−9, and the number of saleable days (when the 5th floret from the base wilted; Fig. 4).

      Figure 4. 

      Stage when 50% of the gladiolus flowers/stem (occurring on genotype GL-8 on day 9) are commercially classified as 'wilted' or 'dead' [24]. Scale: bar = 3 cm.

      Statistical analyses

    • Data were analyzed with univariate general linear model Analysis of Variance (ANOVA) along with mean separations using Tukey's Honestly Significance Difference (HSD) tests at α = 0.05 (Statistical Package for the Social Sciences, SPSS, version 22, University of Chicago, Chicago, IL, USA). Repeated measures ANOVA were used for parameters measured > 1x/stem. Pearson's correlations (r) of all traits were performed. Chi-square (χ2) tests for equal distribution (1:1:1:1:1:1:1:1:1; df = 8; χ2 = 15.507) of the mean number of flowers senesced/day/genotype in days 1−9 and the total number of flowers sensed over the postharvest experiment period (days 1−9) were calculated.

    Results

      Field production experiments

    • All genotypes reached VBD within 10-12 wks from planting (Table 1) and were not significantly different. The range of VBD was within a 3-week range of calendar weeks 32 (GL-1, -4, -9, -10, 'Manhattan') to 34 (GL-2, -3, -11); other genotypes were at week 33. Significant differences were found, however, for flowering calendar week number, ranging from weeks 34 to 37 (Table 1) with the differences ranging from 12 (GL-4, -5, -8, -9, 'Manhattan') to 15 weeks from planting (GL-2; Table 1). Interestingly, GL-2 is a dwarf stature type that took significantly longer to flower than many other genotypes. In contrast, the number of weeks to flowering termination was not significant, with a range of 14−19 wks (Table 1). Genotypes have a flowering date range of 14 wks (98 d) to 19 wks (133 d).

      Plant heights were significantly different among genotypes and ranged from 57 cm or Minimum Length Grade 4+ (GL-2) to 121 cm or Minimum Length Grade 1 (GL-11; Table 1)[16], with the dwarf stature types being significantly shorter than the tall statue types. All adhered to the Stem Strength Grades 1−4 of 15° and fell within the Stem Deviation Curvature of Grade 1 < 5 cm[16]. The significantly tallest genotypes were GL-10 and GL-11 at 117.2 and 120 cm, respectively. Plant width ranged from 13 cm (GL-2, dwarf stature) to 60 cm (GL-9, tall stature; Table 1), although none were not significantly different. Likewise, the number of leaves was insignificant and unrelated to plant statue, despite ranging from 6 (GL-3, -4, -5) to 9 leaves (GL-2; Table 1).ong the numerous and divergent genotypes tested, the phenotypic traits of importance for cut flower use, only flowering week and plant height were significantly different; all other traits were insignificant (Table 1).

      Postharvest experiment

    • Since the gladiolus inflorescence cut stem lengths and numbers of flower buds (florets) per inflorescence (Fig. 3) varied due to varying stem lengths among the dwarf vs tall statures (stem lengths had to be long enough to stand in the preservative solution), there were significant differences within and among treatments (DDW, FLFP) and among most genotypes (Table 2). The interaction of genotype × treatment was not significant. As expected, the shortest two sets of inflorescences in both treatments (DDW, FLFP) had significantly shorter cut stem lengths than all other genotypes, all of which were classified as tall stature types. The significantly tallest inflorescence cut stem lengths occurred in GL-3 for both treatments and would be ranked as Grade 3 for Minimum Length (82 and 91.5 cm, FLFP and DDW, respectively; Table 2)[16]. Most of the other tall stature genotypes overlapped for inflorescence cut stem lengths. As would be expected, inflorescence cut stem lengths were significantly and positively correlated with all traits except for no. flowers senesced/day, Σ no. flowers senesced, final pH, and ΔpH (Table 3).

      Table 2.  Mean inflorescence cut stem length (cm), total no. of floret buds/stem, inflorescence internode length (cm), total no. (%) opened flowers in dwarf and tall stature gladiolus genotypes tested with two treatment solutions applied as continuous vase solutions.

      GenotypeInflorescence cut
      stem length (cm)      		Total no. floret
      buds/stem      		Inflorescence internode
      length (cm)      		Total no. (%) opened flowers
      DDWFLFPPooledDDWFLFPPooled
      Dwarf stature (< 90 cm)
      GL-143.5a42.5a7.7a5.3ab5.8a-c5.1ab (66%)
      GL-2z40.2a37.0a9.5a-c4.2a3.9a2.89a (28%)
      Tall stature (> 90 cm)
      GL-391.5d82.0d17.8g4.8a5.0ab12.2de (68%)
      GL-457.4b64.8bc10.1a-d5.8a-c6.3bd6.2a-c (62%)
      GL-5x65.8bc56.8b13.2e-f4.5a4.8a2.8a (22%)
      GL-665.3bc71.7c11.9c-f5.8a-c5.7a-c6.9a-c (59%)
      GL-7w62.0b73.3c12.9d-f4.9ab5.6a-c5.5ab (43%)
      GL-869.8bc68.3bc10.2a-e6.5cd7.1d9.0cd (88%)
      GL-9w60.0b57.7b9.0ab6.9d6.2bd8.1b-d (90%)
      GL-10w67.0bc69.0bc10.6a-e6.5cd6.3bd10.0c-e (94%)
      GL-11y76.0c68.0bc14.0f5.4a-c4.9ab12.8e (91%)
      'Beatrice'73.5c69.2bc12.3c-f5.9a-c5.7a-c7.2bc (58%)
      'Manhattan'61.8b67.0bc8.3ab7.5d8.4d7.6bc (92%)
      Significancev
      Genotype (G)F = 17.31***F = 13.26***F = 8.29***F = 6.48***
      Treatment (T)F = 13.12***F = 0.63nsF = 3.76*F = 1.33ns
      G × TF = 1.38nsF = 0.66nsF = 0.64nsF = 1.88*
      DDW = deionized, distilled water; FLFP = Floral Life floral preservative or Pooled if treatments were not significantly different. There were n = 6 replications/treatment solution/genotype unless noted otherwise; mean separations within columns based on Tukey's Honestly Significantly Difference (HSD) test at α = 0.05.

      Table 3.  Correlation matrix for the postharvest cut flower traits examined in dwarf and tall stature gladiolus genotypes tested with two treatment solutions applied as continuous vase solutions.

      Day 0
      FW      		Day 9
      FW      		ΔFWDay 9
      DW      		%
      water      		Inflor. cut
      stem length      		Σ no. flw
      buds/stem      		Inflor. internode
      length      		Σ no.
      open flws      		Σ % open
      flws      		Floret
      1 dia.      		Floret 3
      dia.      		No. flws
      senesced
      /day      		Σ no. flws
      senesced      		No. saleable
      days      		Final pHΔpHSol'n vol/stem
      Day 0 FW1.0
      Day 9 FW0.89**1.0
      ΔFW−0.21*0.24**1.0
      Day 9 DW0.91**0.88**0.091.0
      % water−0.010.18*0.26**−0.25**1.0
      Inflor. cut stem length0.81**0.8**0.060.78**0.031.0
      Σ no. flw buds/stem0.68**0.64**−0.070.49**0.24**0.64**1.0
      Inflor. internode length−0.050.030.160.16−0.24**0.21*−0.58**1.0
      Σ no. open flws0.58**0.31**−0.43**0.45**−0.34**0.53**0.39**0.051.0
      Σ % open flws0.23*−0.01−0.39**0.21*−0.51**0.27*−0.18*0.46**0.80**1.0
      Floret 1 dia.0.39**0.37**0.120.49**−0.180.36**0.010.36**0.31**0.32**1.0
      Floret 3 dia.0.35**0.34**0.070.47**−0.180.39**0.010.37**0.34**0.33**0.88**1.0
      No. flws senesced/day−0.07−0.11−0.03−0.04−0.11−0.01−0.010.010.090.060.020.011.0
      Σ no. flws senesced−0.03−0.08−0.010.01−0.14−0.010.02−0.020.030.00−0.01−0.020.94**1.0
      No. saleable days−0.33**−0.020.46**−0.20*0.29**−0.25**−0.34**0.17−0.62**−0.36**−0.19*−0.25**0.010.031.0
      Final pH0.21−0.02−0.53**0.08−0.190.090.070.030.160.130.15−0.050.020.04−0.081.0
      Δ pH−0.27−0.170.21−0.260.12−0.010.03−0.03−0.13−0.13−0.11−0.330.01−0.010.010.131.0
      Sol'n vol/stem0.75**0.79**−0.220.86**−0.090.76**0.460.380.330.240.350.15−0.19−0.230.100.220.191.0
      DDW = deionized, distilled water; FLFP = Floral Life floral preservative or Pooled if treatments were not significantly different.

      An example of the floret opening stage on Day 0, the start of the experiment are shown in Fig. 5. The mean Σ number of floret buds/stem varied significantly across genotypes but not treatments, ranging from 7.7 (GL-1, short stature) Grade 3 flower number/stem to 17.8 Grade 1 flower number/stem (GL-3, tall stature; Table 2)[16]. The interaction of genotype × treatment was not significant. This trait was positively and significantly correlated with Σ no. open flowers (r = 0.39), but negatively and significantly correlated with inflorescence internode length (r = −0.58), Σ % open flowers (r = −0.18) and no. saleable days (r = −0.34; Table 3).

      Figure 5. 

      Example cut gladiolus stems (stage 2) at day 0, the beginning of the experiment, for all six replications of one genotype. Scale: bar = 3 cm.

      The mean inflorescence internode length ranged from 3.9 cm (GL-2, FLFP treatment) to 7.5 cm ('Manhattan', DDW; Table 2). Genotypes and treatments were significant whereas the genotype x treatment interaction was not. This trait was significantly and positively correlated only with reproductive traits, i.e., Σ % open flowers, floret 1 diameter, floret 3 diameter (Table 3). Inflorescence internode length is not a function of, nor correlated with stature, as several significantly shorter internode lengths occurred in both the short and tall statures, whereas only the significantly longest internodes occurred in the tall stature genotypes (Table 2).

      The Σ number and Σ percent of opened flowers/inflorescence at the end of the experiment, ranged from 2.8% and 22% (GL-5) to 12.8% (GL-11) and 94% (GL-10; Table 2), respectively. The significantly lowest percentages of opened flowers/inflorescence occurred in both short (GL-2, 28%) and taller stature (GL-5, 22%) genotypes. An example of the flower opening/closing on Day 9 is shown for a single stem (Fig. 6) versus all stems within a genotype (Fig. 7). In some instances, flowers never opened in both solution treatments (Fig. 8). Genotypes differed significantly although treatments did not but their interaction was significant (Table 2). Both traits were significantly and positively correlated with each other (r = 0.8) as well as each trait with floret 1 and 3 diameters, but negatively and significantly correlated with the number of saleable days (r = −0.62, r = −0.36, respectively; Table 3).

      Figure 6. 

      Gladiolus stem post-stage when > 50% of the gladiolus flowers have wilted (GL-11 rep 1 on day 9). Scale: bar = 3 cm.

      Figure 7. 

      Set of six replicate gladiolus stems (GL-6 stems all reps) at the end of the experiment on day 9. Scale: bar = 3 cm.

      Figure 8. 

      Example of gladiolus flowers failing to open completely (GL-6 rep 2 stem on day 9). Note: This genotype often produced a secondary flowering shoot (left). Scale: bar = 3 cm.

      As would be expected, Day 0 stem FWs were not significantly different among treatments since the experiment had not yet commenced. However, genotypes were very highly significantly different, ranging from 9.9 g (GL-2, short stature) to 54.9 g (GL-3, tall stature; Table 4). The interaction of genotype × treatment was not significant. Day 0 FW were positively and significantly correlated with day 9 FW (r = 0.89) and DW (r = 0.91), inflorescence cut stem length (r = 0.81), Σ number of flower buds/stem (r = 0.68), Σ number of open flowers (r = 0.58), Σ % open flowers (r = 0.23), floret 1 diameter (r = 0.39), floret 3 diameter (r = 0.35), and solution volume/stem (r = 0.75; Table 3). Day 0 FW was significantly but negatively correlated with the number of saleable days (r = −0.33; Table 3); all other trait correlations were not significant.

      Table 4.  Mean day 0 stem fresh weight (FW; g), day 9 stem FW (g), ΔFW (g; day 9 FW – day 0 FW), day 9 dry weight (DW; g), % water in dwarf and tall stature gladiolus genotypes tested with two treatments applied as continuous vase solutions.

      GenotypeDay 0 stem FW (g)Day 9 stem FW (g)ΔFW (g)Day 9 DW (g)% Water
      PooledDDWFLFPDDWFLFPDDWFLFPDDWFLFP
      Dwarf stature (< 90 cm)
      GL-115.8ab13.9ab14.6ab−2.8a-d−0.2b-d1.9a2.0a75.8b75.4b
      GL-2z9.9a8.7a9.9a−3.2a-d1.8cd1.2a0.9a75.2b82.2bc
      Tall stature (> 90 cm)
      GL-3y54.9g47.7g50.1−15.1a3.0cd5.0e-g5.5fg80.9bc80.2bc
      GL-421.9a-c17.7a-c27.3b-e−1.6b-d2.8cd2.5ab3.4a-d75.6b77.8bc
      GL-5x24.3a-d30.1c-e25.6b-e1.3cd5.6d2.3ab1.2a85.8c90.9cd
      GL-638.4d-f30.6c-e46.9g−5.9ab6.7d3.7b-e4.5c-g78.6bc82.4bc
      GL-7w44.4e-g37.4d-f53.6g−6.2a8.2d5.1e-g5.9g76.0bc80.2bc
      GL-822.2a-c29.4b-e42.2e-g−12.4a9.5d4.4c-g5.1e-g74.1b78.7c
      GL-9w27.4b-d16.3a-c19.1a-c−11.4a−7.9a3.2a-d3.8b-e66.7a67.2a
      GL-10w29.6b-e24.1a-d31.1c-e−1.6b-d−2.2b-d3.3a-d4.2b-g76.1bc76.0bc
      GL-11y34.2c-f27.2b-e31.4c-e−6.6a3.8cd4.3c-g3.7b-e72.8ab71.1ab
      'Beatrice'46.9fg42.5e-g54.5g−2.2a-d5.3d5.1e-g5.8g78.7c80.7bc
      'Manhattan'30.8b-e25.4b-e31.3c-e−3.2a-d−1.6b-d3.1a-d3.7b-e78.0c78.6c
      Significancev
      Genotype (G)F = 15.54***F = 20.99***F = 5.45***F = 14.39***F = 21.80***
      Treatment (T)F = 0.52nsF = 22.42***F = 125.45***F = 43.82***F = 19.69***
      G × TF = 1.45nsF = 1.48nsF = 4.99***F = 1.47nsF = 1.54ns
      DDW = deionized, distilled water; FLFP = Floral Life floral preservative or Pooled if treatments were not significantly different.
      There were n = 6 replications/treatment solution/genotype unless noted otherwise; mean separations within columns based on Tukey's Honestly Significantly Difference (HSD) test at α = 0.05.

      Day 9 stem FWs were very highly significantly different for both genotypes and treatments, but not for their interaction (Table 4), ranging from 8.7 g (GL-2, DDW) to 54.5 g ('Beatrice', FLFP). This range was slightly lower than the range for Day 0, as illustrated by the ΔFW wherein most genotypes had negative ΔFW (−0.2 to −15.1). The exceptions occurred primarily in the FLFP treatment in both dwarf and tall stature genotypes; the only positive ΔFW in the DDW treatment was GL-5 (ΔFW = 1.3; Table 4). Day 9 FW were significantly and positively correlated with all traits except inflorescence internode length, Σ % open flowers, number of flowers senesced/day, Σ number of flowers senesced, final pH, and Δ pH (Table 3).

      The percent water ranged from 66.7% (GL-9, DDW) to 90.9% (GL-5, FLFP; Table 4), based on fresh weight – dry weight differences. The lowest percent water occurred in tall stature genotypes instead of the dwarf genotypes. The lowered level of water in some genotypes, e.g. GL-9 might indicate increased levels of fibers in the stem stalks and/or leaves but would need to be studied further to identify the root cause of depressed percent water.

      The 1st flower (floret) diameters were very highly significant for genotypes and treatments but only highly significantly different for their interaction (genotype x treatment; Table 5). The mean range of flower diameters for the 1st flower was 4.1–7.8 cm for DDW (miniature) and 4.6–8.1 cm for FLFP treatments (miniature). While most means overlapped in significance, there were genotypes with the significantly smallest (GL-6) and largest 1st flower diameters (GL-7 to GL-11, 'Beatrice' and 'Manhattan') in the DDW treatment (Table 5). Comparatively, the FLFP treatment smallest 1st flower diameters were GL-4 and GL-6, as opposed to the significantly largest diameters occurring in GL-3, GL-8 to GL-11, 'Beatrice' and 'Manhattan'. Thus, GL-6 consistently had the smallest 1st flower diameter in both treatments, whereas GL8 to GL-11, 'Beatrice', and 'Manhattan' consistently had the significantly largest 1st flower diameters (Table 5). The 1st flower diameter was significantly and positively correlated with all other traits except for ΔFW, % water, Σ number of flower buds/stem, number of flowers senesced/day, Σ number of flowers senesced, final pH, ΔpH, and solution vol./stem (Table 3).

      Table 5.  Mean 1st flower diameter (cm), 3rd flower diameter (cm), final pH, ΔpH, solution volume used per stem (ml) in dwarf and tall stature gladiolus genotypes tested with two treatment solutions applied as continuous vase solutions.

      Genotype1st Flower diameter (cm)3rd Flower diameter (cm)Final pH (ΔpH)Sol'n vol./stem (ml)
      DDWFLFPDDWFLFPDDWFLFPDDWFLFP
      Dwarf stature (< 90 cm)
      GL-15.5a-d6.5d-g4.8a5.4a-d4.9 (3.4)3.5 (0.6)1.73.3
      GL-2z5.0a-d5.0a-d4.2a6.2b-e4.9 (3.4)4.2 (−0.09)53.2
      Tall stature (> 90 cm)
      GL-3y7.5g7.2fg6.2b-e5.6a-d4.9 (3.5)4.2 (−0.1)3535
      GL-45.0a-d4.8ab5.1a-c4.7a5.3 (3.1)4.1 (−0.04)16.816.7
      GL-5x5.8b-e6.0c-f5.2a-c5.3a-d4.2 (4.2)4.1 (−0.02)2820
      GL-64.1a4.6ab3.9a4.1a4.9 (3.5)4.2 (−0.1)21.721.7
      GL-7w7.5g5.0a-d5.5a-d5.5a-d4.9 (3.4)4.8 (−0.7)2030
      GL-87.5g7.2fg6.8de6.3b-e5.1 (3.3)4.1 (−0.1)3025
      GL-9w7.8g6.8e-g6.3b-e5.8a-d5.1 (3.3)4.2 (−0.1)6.75
      GL-10w7.2fg7.7g6.1b-e7.3e5.0 (3.4)4.2 (−0.1)6.710.3
      GL-11y7.0fg6.5d-g6.2b-e6.0b-e5.2 (3.2)4.1 (−0.05)3030
      'Beatrice'6.8e-g7.8g6.1b-e7.8e4.4 (3.9)4.5 (−0.4)6050.8
      'Manhattan'7.0fg8.1g6.0b-e7.0e5.2 (3.2)4.1 (−0.05)6060
      Genotypes Pooled4.92 (3.45)b4.24 (−0.1)a24.7ab23.9a
      Significancev
      Genotype (G)F = 15.51***F = 8.19***F = 0.22nsF = 1.10ns
      Treatment (T)F = 20.59***F = 14.66***F = 13.87***F = 1.91*
      G × TF = 2.27**F = 2.51**F = 0.91nsF = 0.96ns
      z n = 4 reps. y n = 2 reps. x n = 5 reps. w n = 3 reps. v *** p < 0.001, ** p < 0.01, * p < 0.05, ns not significant.
      DDW = deionized, distilled water; FLFP = Floral Life floral preservative or Pooled if treatments were not significantly different.
      There were n = 6 replications/treatment solution/genotype unless noted otherwise; mean separations within columns based on Tukey's Honestly Significantly Difference (HSD) test at α = 0.05.

      Similar to the 1st flower diameters, the 3rd flower diameters were also very highly significant for genotypes and treatments but only highly significantly different for their interaction (genotype × treatment; Table 5). The mean range of flower diameters for the 3rd flower in the DDW treatment was 3.9 cm (GL-6; miniature) to 6.8 cm (GL-8; small) and 4.1 (GL-6; miniature) to 7.8 cm ('Beatrice'; miniature) in the FLFP. Similar to 1st flowers, GL-6 also displays genetic stability across treatments for the smallest 3rd flower diameters (Table 5).

      Final pH of the vase solution treatments was not significantly different among genotypes or genotype x treatment interaction but was very highly significantly different for treatment (Table 5). While the beginning pH of the water was pH = 8.38, prior to adding floral preservative to FLFP, as soon as it was added the FLFP starting pH decreased to pH = 4.07. With the exception of ΔFW (r = −0.53), all final pH correlations with other traits were nonsignificant and nearly zero (Table 3).

      Final pH values for the DDW treatment reduced significantly from the beginning (pH = 8.38) with a pooled mean of pH = 4.92 and ranging from pH = 4.2 (GL-5) to pH = 7.8 ('Beatrice') across genotypes although the means were not significantly different (Table 5). In most cases of DDW where the final pH was the highest, the inflorescence cut stem lengths were significantly longer and total number of floret buds/stem were significantly higher (Table 2). Thus, the inflorescence cut stem length and/or total number of floret buds/stem may be inferred to require additional solution changes during the test period to eliminate potentially higher levels of phloem unloading. Pooled mean final pH values for the FLFP treatment was pH = 4.24, significantly lower than that of DDW (Table 5). Specific genotype pH ranged from pH = 3.5 (GL-1) to pH = 4.8 (GL-7), although they did not differ significantly.

      Solution volume used / stem (uptake) were not significantly different for genotypes or genotype × treatment interactions but significantly different for treatments (Table 5). Pooled genotypic means were 24.7 ml (DDW), with significantly more solution volume used / stem than FLFP (23.9 ml) although they overlapped (Table 5). Four traits had positively and highly significant correlations with solution volume used / stem: day 0 FW (r = 0.75), day 9 FW (r = 0.79), day 9 DW (r = 0.86), and inflorescence cut stem length (r = 0.76; Table 3); all other traits were not correlated.

      The ANOVAs for mean number of flowers senesced/day (days 1−9) and Σ number of flowers senesced (days 1-9) showed significance for genotypes, but not for treatments or their interactions (Table 6). The mean number of flowers senesced/day ranged from 0.1 (GL-5, GL-7) to 0.6 (GL-8; Table 6). GL-2, -3, -5, -7, and -11 all had significantly less flowers senesced/day than GL-4, -8, and 'Manhattan'; the remaining genotypes all overlapped. For the Σ number of flowers senesced (days 1-9), mean values ranged from 0.85 (GL-5) to 6.8 (GL-8; Table 3). GL-2, -5, -11, and 'Beatrice' had significantly lower number of flowers senesced over the 9-day period than GL-4, -8, and 'Manhattan' (Table 3). Lower numbers of senescing flowers/day or in total would be ideal traits to breed and select for to enhance postharvest longevity, instead of higher numbers (faster senescence). Neither trait was not significantly correlated with any other trait excepting each other (r = 0.94; Table 3). All Chi-square (χ2) tests for equal distribution (1:1:1:1:1:1:1:1:1; df = 8; χ2 = 15.507) of the mean number of flowers senesced/day/genotype in days 1−9 and the total number of flowers sensed over the postharvest experiment period (days 1−9) in dwarf and tall stature gladiolus genotypes were not significant (Table 7), indicating that the rate of flower senescing per day or in total was the same (linear), regardless of genotype.

      Table 6.  Mean number of flowers senesced/day in days 1−9, total number of flowers sensed in days 1-9, and number of saleable days (when the 5th floret from the base wilted) in dwarf and tall stature gladiolus genotypes tested with two treatment solutions applied as continuous vase solutions.

      GenotypeNo. of
      flowers
      senesced/day
      (days 1−9)      		Total no.
      of flowers
      senesced
      in days 1−9      		No. of
      saleable days
      PooledPooledDDWFLFP
      Dwarf stature (<90 cm)
      GL-10.35ab3.05ab8.0e8.0e
      GL-2z0.15a1.10a7.5b-e8.0e
      Tall stature (>90 cm)
      GL-3y0.25a2.25ab5.5a7.0b-e
      GL-40.50b4.65b7.7c-e7.5b-e
      GL-5x0.10a0.85a7.0b-e8.0e
      GL-60.45ab3.85ab7.8c-e8.0e
      GL-7w0.10a1.10a6.0a8.0e
      GL-80.60b6.80b6.7bc7.8c-e
      GL-9w0.35ab3.15ab7.0b-e6.0a
      GL-10w0.40ab3.2ab6.7bc6.7bc
      GL-11y0.25a2.25a3.0a4.5a
      'Beatrice'0.35ab2.95a7.8c-e8.0e
      'Manhattan'0.50b4.5b8.0e7.3b-e
      Significancev
      Genotype (G)F = 2.446**F = 1.98*F = 9.98***
      Treatment (T)F = 0.55nsF = 0.69nsF = 4.47**
      G × TF = 0.69nsF = 0.73nsF = 1.69*
      z n = 4 reps. y n = 2 reps. x n = 5 reps. w n = 3 reps. v *** p < 0.001, ** p < 0.01, * p < 0.05, ns not significant.
      DDW = deionized, distilled water; FLFP = Floral Life floral preservative or Pooled if treatments were not significantly different.
      There were n = 6 replications/treatment solution/genotype unless noted otherwise; mean separations within columns based on Tukey's Honestly Significantly Difference (HSD) test at α = 0.05.

      Table 7.  Frequencies and Chi-square (χ2) tests for equal distribution (1:1:1:1:1:1:1:1:1; df = 8; χ2 = 15.507) of the mean number of flowers senesced/day/genotype in days 1−9 and the total number of flowers sensed over the postharvest experiment period (days 1−9) in dwarf and tall stature gladiolus genotypes tested with two treatment solutions applied as continuous vase solutions.

      GenotypeTreatmentMean no. of flowers senesced/day/genotypeχ2 (sig.)
      Day 1Day 2Day 3Day 4Day 5Day 6Day 7Day 8Day 9
      Dwarf stature (< 90 cm)
      GL-1DDW0.000.000.000.670.170.670.500.830.33.82nsz
      FLFP0.000.000.001.000.170.500.671.000.43.07ns
      GL-2DDW0.000.170.000.330.170.330.170.330.25.92ns
      FLFP0.000.170.000.170.000.170.000.170.17.51ns
      Tall stature (> 90 cm)
      GL-3DDW0.000.170.500.500.330.330.170.330.304.51ns
      FLFP0.170.330.170.330.330.330.170.330.204.90ns
      GL-4DDW0.000.000.670.831.000.830.501.000.501.50ns
      FLFP0.000.170.500.670.670.830.671.000.501.77ns
      GL-5DDW0.000.000.170.170.170.170.170.170.106.90ns
      FLFP0.000.000.000.170.000.170.170.170.107.51ns
      GL-6DDW0.000.000.830.330.830.830.671.000.501.79ns
      FLFP0.000.000.500.330.670.500.500.670.403.28ns
      GL-7DDW0.170.170.330.330.330.330.330.170.204.90ns
      FLFP0.000.000.000.000.000.000.000.000.009.00ns
      GL-8DDW0.830.500.830.671.000.501.001.000.700.43ns
      FLFP0.170.500.500.501.000.500.500.500.502.08ns
      GL-9DDW0.000.500.170.500.500.330.500.500.303.61ns
      FLFP0.330.500.330.500.330.500.330.500.403.10ns
      GL-10DDW0.000.170.500.500.500.500.500.500.403.28ns
      FLFP0.000.170.500.500.500.500.500.500.403.28ns
      GL-11DDW0.000.330.170.170.170.170.170.170.206.17ns
      FLFP0.330.500.330.330.330.330.330.330.303.85ns
      'Beatrice'DDW0.000.000.170.500.830.500.500.670.403.28ns
      FLFP0.000.000.001.000.170.170.001.330.304.04ns
      'Manhattan'DDW0.000.000.670.500.830.170.830.830.402.53ns
      FLFP0.000.170.670.670.830.831.001.000.601.16ns
      z ns not significantly different from the null hypothesis that the number of flowers senesced/day do not differ.
      DDW = deionized, distilled water; FLFP = Floral Life floral preservative.

      The number of saleable days (when the 5th floret from the base wilted) in dwarf and tall stature gladiolus genotypes tested with two treatment solutions ranged from 3 d (GL-11) to 8 d (GL-1, 'Manhattan') for DDW and 4.5 d (GL-11) to 8 d (GL-1, -2, -5, -6, -7, 'Beatrice') for FLFP vase treatment solutions (Table 6). The lowest number of saleable days were significantly lower than the highest values found, indicating significant genetic differences among the germplasm tested with particularly different results among the two comparison cultivars. The number of saleable days was negatively but significantly correlated with eight traits (day 0 FW, day 9 DW, inflorescence cut stem length, Σ number of flower buds/stem, Σ number of open flowers, Σ % open flowers, floret 1 diameter, floret 3 diameter) or positively and significantly correlated with two traits (ΔFW, % water; Table 3). These negative or positive significant correlations will be important to direct future breeding efforts and select for enhanced postharvest life.

    Discussion

      Field production experiments

    • VBD occurred within a tight 3-week window among all genotypes, regardless of stem height (Table 1). When categorizing flowering time by the North American Gladiolus Council classifications, GL-4, -5, -8, -9, and 'Manhattan' are midseason (84 d); GL-1, -3, -6, -7, -10, -11, and 'Beatrice' are late (91-99 d) flowering; GL-2 is very late (> 100 d)[11]. While early types exist in the breeding program, by chance they were not selected for this study. Future research into earlier VBD types might reveal faster leaf unfolding rates; potential genotypes to research would be our cycle 1 RGC which flower in the first year in < 1 yr from seed[8,26,27]. Classification of genotypes by flowering date ranged from late (14 wks or 98 d) to very late (19 wks or 133 d; Table 1)[9,10].

      The significant differences in plant height were such that the tested genotypes were categorized from Grades 1-4 for Minimum Length Grade to 117.2 (GL-10) - 121 cm (GL-11; Table 1)[16]. Since taller genotypes exist, both in the UMN breeding program (137 cm is the tallest found; Anderson, 2021, unpublished data) and elsewhere (183 cm)[33], the significance of plant height differences could be further accentuated, although stems taller than GL-10 and -11 (Grade 1) would exceed the grading standards.

      Among the numerous and divergent genotypes tested for phenotypic traits of importance for cut flower use, only flowering week and plant height were significantly different; all other traits were not significant (Table 1). If this germplasm sampling is an accurate reflection of gladiolus cut flower genotypes, then future breeding and selection efforts should be focused on these two traits without regards to the others (no. weeks to VBD, flowering termination week number, plant width, no. leaves).

      Postharvest experiment

    • Short- and tall-stature genotypes differed significantly for inflorescence cut stem length, matching plant height findings which infers that most of the plant height is influenced by the inflorescence length, rather than leaf internode lengths. Plant height would not need further analyses, rather only measurements of inflorescence cut stem lengths. Since inflorescence cut stem lengths were significantly and positively correlated with most traits (Day 0, 9 FW, Day 9 DW, Σ no. flower. buds/stem, inflorescence internode length, Σ no. or % open flowers, 1st and 3rd flower diameter, solution volume/stem), they may be linked traits to aid in co-selection all traits. Future research will determine whether the traits share similar single nucleotide polymorphisms (SNPs) or map to a single chromosome which would aid in marker-assisted selection.

      Since the Σ number of floret buds/stem varied significantly among genotypes, it could be a heritable trait for increased production capacity/stem. This trait hasn't been examined in previous postharvest studies[19,24,32], but is a critical trait of floriferousness that gladiolus breeding programs would want to breed and select for increased 'flower power'[34].

      Unlike what might be expected, inflorescence internode length is not correlated with stature (Table 3), since several significantly shorter internode lengths occurred in both the short and tall statures. However, only the significantly longest internodes occurred in the tall stature genotypes (Table 2) which may mean a threshold internode length has to be reached before this is correlated with plant stature. The ideal internode length could vary, depending on the flower size (miniature or < 6.3 cm to giant > 14 cm) and flower number, as long as stem strength is adequate[35].

      The Σ number and Σ percent of opened flowers/inflorescence of 2.8 (22%; GL-5) to 12.8 (GL-11) and 94% (GL-10; Table 2), respectively, exceeded the range of previous reports[19]. In some cases, the lower values were due to flowers which would not open (Fig. 8), regardless of solution treatment. Previous research found varying opened flowers/inflorescence in 'White Prosperity' (36.3%−84.1%) under various treatment solutions in two experiments[19], while other studies did not record this trait[24,32]. Both traits are important to assess salability and flower power for cut flower usage.

      Previous research did not find significant genotypic differences for FWs among 'American Beauty' and 'Snow Princess'[24], although this lack of significant FWs may be due to either the low number of genotypes tested or similar responses among the two cultivars. Thus, the increased number of genotypes in the present study have greater genetic diversity and provide new insights into FW levels. Day 0 stem FWs of both dwarf stature genotypes (GL-1, GL-2) overlapped with several tall stature types (GL-4, GL-5, and GL-8), which was unexpected.

      Day 9 stem FWs differed significantly among genotypes and treatments (Table 4) with a wide range in expression (8.7 g, GL-2, DDW to 54.5 g, 'Beatrice', FLFP). In previous research, FWs and ΔFW changed significantly within 'White Prosperity', based on post-harvest solution treatments, although all ΔFW were positive in most of the silver-based treatments except for tap water, 0.01, and 0.1 mg·L−1 nano-silver continuous vase solutions[19].

      The 1st flower diameters classified the many of the genotypes as miniature[10,11,16,35]. GL-6 consistently had the smallest 1st flower diameter in both treatments, whereas GL-8 and GL-11, 'Beatrice', and 'Manhattan' respectively, consistently had the significantly largest 1st flower diameters (Table 5). For all genotypes tested, the 1st flower diameters were smaller than those previously reported for 'American Beauty' (11.18 cm; small) and 'Snow Princess' (11.16 cm; small)[11,24] but similar in dimensions to 'White Prosperity' (6.5−9.1 cm; miniature to small)[11,19]. These differences could be either genetic, environmental or physiological with less reserved carbohydrates available for the 1st or basal floret[36]. Genotypic stability for the 1st flower diameter exhibited by the tested genotypes make them valuable germplasm for breeding purposes.

      The 3rd flower diameters of 3.9 cm (GL-6; miniature) in the DDW treatment, to 7.8 cm ('Beatrice'; miniature) in FLFP, were all smaller floral diameters than reported for 'American Beauty' (9.98 cm; small) and 'Snow Princess' (9.74 cm; small)[11,16]. GL-6 also displays genetic stability across treatments for the smallest 3rd flower diameters, regardless of solution treatment (Table 5). This genetic stability, regardless of preservative solutions is of value for future breeding efforts.

      As would be expected, final pH differed by treatment solutions. The final pH values were consistently lowest in all genotypes treated with FLPP (Table 5), as would be expected with floral preservatives[11,19,24,32,35]. It would be important to maintain current recommendations of floral preservatives to maximize gladiolus postharvest life by ensuring the solution pH most closely matches that of cell pH.

      While previous studies have not reported measuring ending pH for treatments or gladioli genotypes, our data provide an insight into the ability of cut gladiolus to decrease solution pH without added floral preservatives. These findings were completely unexpected and show the resilience of cut gladiolus as a cut flower crop for floral designs[2]. The implications of inflorescence cut stem lengths and total number of floret buds/stem on final pH are important considerations for future breeding and selection of the cut flower crop.

      Solution treatments had little to no effect on solution volume used per stem, despite having floral preservatives recommended to increase gladiolus vase life[21]. The highest solution volume used per stem of 60 ml ('Beatrice', 'Manhattan') matched similar levels for 'Friendship' over the same treatment period of 9 d[32]. Solution uptake volumes for other genotypes were lower than that of 'Friendship'. 'American Beauty' and 'Snow Princess' had slightly higher levels of solution volume used per stem (71.68−77.28 ml) over a 12-d period than our results[24].

      The range of saleable days was surprisingly similar despite not having floral preservative in one of the treatments (DDW). However, since the consumer vase life expectancy is 6−10 d[21], any genotypes with < 6 d vase life would not be recommended as cut gladioli.

      The similar rate of flower senescing per day or in total was the same (linear) and independent of genotype. This demonstrates consistent flower aging, regardless of vase solutions, across the postharvest test environment which will benefit the grower, distributor, wholesaler, retailer as well as the consumer. To the best of our knowledge, the heritability of these traits are unknown.

    Conclusions

    • Since genotype effects were significant for all traits examined except for final pH and solution volume/stem (Table 2), a wide range of genetic variation exists across the dwarf vs. tall stature types for the remaining traits tested, indicating potential for continued breeding, selection, and improvement of cut flower gladiolus for the floricultural industry. Genotypes were either midseason, late or very late in flowering time; it had been expected that the dwarf or short stature types would have been earlier flowering. The lack of early flowering in these types may be due to slowed leaf unfolding or floral scape development despite the significantly shorter stem lengths; future research could clarify these developmental rates to be equalized across stem length (plant and inflorescence height). Surprisingly, GL-11 was taller than the two cultivars and classified as Minimum Length Grade 1. Leaf number variation (ranging from 6 to 9) was unexpected and may have genetic heritability which would impact selection for earlier flowering due to increased leaf unfolding time in those genotypes with higher leaf numbers. Floral preservative versus the control (no floral preservative) had significant effects on all traits except for total number of floret buds/stem, total number (%) of opened flowers, day 0 stem FW, number of flowers senesced / day (days 1−9), and total number of flowers senesced in days 1−9. Thus, the recommended incorporation of floral preservative to maximize floret opening, life (d), and overall performance warrants its continued use with this crop, although our study suggests that, for some genotypes, changing the vase solution > 1x/week would be warranted. However, the decrease in solution pH for the DDW treatment was unexpected and warrants further study on the content of phloem unloading in cut gladiolus. Heritability of all traits included herein should be studied in programmed crosses, coupled with molecular marker creation to aid in selection. To the best of our knowledge, only cold tolerance heritability has been studied in gladiolus[8]. While several genes have been identified at the molecular level, e.g. UPSTREAM OF FLOWERING LOCUS C (UFC) and FLOWERING LOCUS C EXPRESSOR (FLX)[25], the gibberellin receptor gene[37], and two ubiquitin promoters (GUBQ2, GUBQ4)[38], the gladiolus genome has yet to be sequenced, GWAS and marker-assisted selection have yet to be created and implemented to complement classic gladiolus breeding programs. Data from this study and others will be used to formulate a new cut flower gladiolus crop ideotype to direct breeding and selection efforts for public- and private-sector gladiolus breeding programs, similar to other cut flower floricultural crops such as perennial flax[39,40] and chrysanthemum[41].

      Acknowledgments

      • Funding in support of this publication was from the Minnesota Gladiolus Society and the Minnesota Agricultural Experiment Station.

      Conflict of interest

      • The author declares that there is no conflict of interest.

      Rights and permissions
      • Copyright: © 2023 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
    Figure (8)  Table (7) References (41)
  • About this article
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    Anderson NO. 2023. Gladiolus cut flower postharvest performance to direct breeding efforts. Technology in Horticulture 3:21 doi: 10.48130/TIH-2023-0021
    Anderson NO. 2023. Gladiolus cut flower postharvest performance to direct breeding efforts. Technology in Horticulture 3:21 doi: 10.48130/TIH-2023-0021
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  • Postharvest experiment

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  • Discussion

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