Assessment of fruit quality and volatile profiles in watermelons grafted onto various rootstocks

Wanbang Yang; Jinyu Zhou; Rong Yu; Huiying Du; Mei Tian; Song Guo; Hao Li; Yanzi Zhang; Yuan Yu; Wanbang Yang; Jinyu Zhou; Rong Yu; Huiying Du; Mei Tian; Song Guo; Hao Li; Yanzi Zhang; Yuan Yu

doi:10.48130/vegres-0024-0034

Figures (3) Tables (7)

Figure 1.
PCA and HCA of fruit characteristics for 'Ningnongke huadai' watermelon grafted onto various rootstocks. (a) PCA score, and (b) loading plots of fruit characteristics. (c) HCA of fruit characteristics. Each row in the figure corresponds to a distinct fruit trait and each column to a specific sample. The color gradient represents the relative magnitudes of the fruit characteristics across the sample groups. The dendrogram at the top indicates the clustering of samples, with the sample names listed below.
Figure 2.
Multivariate statistical analysis of volatile profiles for 'Ningnongke huadai' watermelon grafted onto different rootstocks. (a) Number, and (b) relative content of volatile compounds in each chemical class. (c) Venn diagram analysis of volatile compounds. (d) PCA score plot of volatile compounds that were identified as differentially accumulated among watermelon samples. (e) HCA of volatile compounds that were identified as differentially accumulated among watermelon samples. Each column in the figure corresponds to a sample, and each row to a volatile compound. The color coding indicates the relative content of volatile compounds in the respective sample groups. On the left, the dendrogram illustrates the clustering of volatile compounds, whereas the top dendrogram shows the clustering of samples, with sample names listed below.
Figure 3.
Comparative analysis of volatile compounds in 'Ningnongke huadai' watermelon grafted onto different rootstock types. (a) Number of differentially accumulated volatile compounds identified in watermelons grafted onto each rootstock type compared to the non-grafted watermelons (p < 0.05). Red bars represent volatile compounds that were more abundant, while blue bars indicate those that were less abundant in the grafted watermelons compared to the non-grafted. The boxplots show the relative contents of volatiles in each chemical class among watermelon samples including (b) alcohols, (c) aldehydes, (d) aromatic hydrocarbons, (e) ketones, and (f) total volatiles. Groups denoted by the same letter are not significantly different as determined by Tukey's honestly significant difference test at p < 0.05.

Rootstock	Abbreviation	Type
Yongshi	YS	Wild watermelon (Citrullus lanatus subsp. Lanatus)
Ningzhen 101	NZ101	Wild watermelon (Citrullus lanatus subsp. Lanatus)
Yezhuang 1	YZ1	Wild watermelon (Citrullus lanatus subsp. Lanatus)
Jingxinzhen 1	JX1	Bottle gourd (Lagenaria siceraria Standl.)
Sizhuang 111	SZ111	Bottle gourd (Lagenaria siceraria Standl.)
Jingxinzhen 2	JX2	Pumpkin (Cucurbita maxima × Cucurbita moschata)
Zhuangshi	ZS	Pumpkin (Cucurbita maxima × Cucurbita moschata)
Ningzhen 1	NZ1	Pumpkin (Cucurbita maxima × Cucurbita moschata)
Mingxiu	MX	Pumpkin (Cucurbita maxima × Cucurbita moschata)
Jinchengxuefeng	JC	Pumpkin (Cucurbita maxima × Cucurbita moschata)
Qingyou 1	QY1	Pumpkin (Cucurbita maxima × Cucurbita moschata)

Table 1.

Eleven rootstocks for 'Ningnongke huadai' watermelon.

Type	NG	Wild watermelon			Bottle gourd		Pumpkin
Type	NG	NZ101	YS	YZ1	JX1	SZ111	JC	MX	QY1	ZS	JX2	NZ1
Fruit weight (kg)	10.41^h	11.76^ef	12.01^de	10.94^fgh	11.36^efg	10.78^gh	14.22^a	14.08^a	12.64^cd	13.54^ab	11.50^efg	12.97^bc
Fruit length (cm)	22.62^cd	24.17^bcd	23.77^cd	26.32^ab	23.50^cd	22.80^cd	27.12^a	24.38^bc	23.97^bcd	21.81^d	23.78^cd	23.30^cd
Fruit width (cm)	29.65^c	32.99^abc	31.98^abc	31.38^bc	35.00^ab	34.05^abc	35.68^ab	37.03^a	35.15^ab	31.33^bc	35.61^ab	34.55^abc
Rind thickness (cm)	1.05^bc	1.13^b	1.15^b	1.30^a	1.12^b	0.95^cd	0.87^def	0.92^cd	0.88^de	0.73^fg	0.75^efg	0.66^g
Rind firmness (kg/cm²)	15.21^abc	16.65^a	14.69^bc	14.90^abc	14.56^bcd	16.02^ab	14.90^abc	14.88^bc	14.02^cd	12.82^d	15.84^ab	14.32^bcd
Flesh firmness (kg/cm²)	0.63^e	0.53^e	0.59^e	0.61^e	0.77^cde	0.70^de	1.03^ab	0.97^abc	1.19^a	1.08^ab	0.93^bcd	1.14^ab
Central soluble solids (°Brix)	11.30^bcd	12.17^a	11.93^ab	11.67^abc	10.40^ef	10.80^def	9.98^f	10.48^def	10.30^ef	10.85^cde	10.72^def	10.87^cde
Edge soluble solids (°Brix)	8.05^abc	8.02^abc	8.40^a	7.47^bc	7.65^abc	7.72^abc	8.17^abc	7.43^bc	7.37^c	7.83^abc	8.27^ab	8.42^a
All values are mean of three biological replicates (six fruits each) per grafting combination. Distinct letters within the same row indicate statistically significant differences, as determined by Student's t test at p < 0.05.

Table 2.

Fruit quality characteristics of 'Ningnongke huadai' watermelon grafted onto different rootstocks.

Code	Compound	Class	RI (Caculated)	RI (Published)^b	NG	NZ101	YS	YZ1	JX1	SZ111	JC	MX	QY1	ZS	JX2	NZ1
3	2-methyl-1-butanol	alcohol	726	724	0.14^z	0.08^zy	0.11^zy	0.10^zy	0.11^zy	0.13^zy	0.05^zy	0.05^zy	0.05^zy	0.06^zy	0.04^zy	0.04^y
6	dimethyl disulfide	sulfide	728	785^c	0.02	0.06	0.04	0.02	0.22	0.39	0.02	0.03	0.02	tr	0.19	tr
10	2-methyl-3-pentanone	ketone	731	745^d	0.02	0.01	0.01	0.01	0.02	0.01	0.01	0.02	0.04	0.02	0.01	0.01
13	(E)-2-pentenal^a	aldehyde	734	744	0.07^zy	0.08^zy	0.07^y	0.07^zy	0.06^y	0.08^zy	0.07^zy	0.09^zy	0.16^z	0.11^zy	0.06^y	0.07^zy
17	pentanol^a	alcohol	741	762	0.26	0.25	0.19	0.23	0.19	0.19	0.17	0.18	0.29	0.24	0.15	0.18
20	(Z)-2-pentenol^a	alcohol	743	765	0.01	0.01	0.01	0.01	tr	0.01	0.01	0.01	0.01	0.01	tr	0.01
21	2-methyl-3-pentanol	alcohol	745	775^d	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
29	2-methyl-4-pentenal	aldehyde	757	793^d	tr	tr	tr	0.01	tr	0.01	0.01	0.02	0.02	0.02	tr	tr
31	2,3-butanediol	alcohol	760	785	tr	0.02	nd	0.04	tr	0.01	0.03	0.01	0.03	0.02	nd	0.01
33	hexanal^a	aldehyde	764	801	2.88^zy	2.86^zy	2.02^y	2.56^zy	2.52^zy	2.90^zy	2.93^zy	2.97^zy	5.35^z	3.91^zy	2.75^zy	2.70^zy
38	2,4-dimethyl-heptane	aromatic hydrocarbon	783	822^d	tr	tr	tr	tr	0.01	0.01	tr	tr	tr	tr	tr	tr
41	pentyl formate	ester	789	797^d	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
43	propylcyclopentane	aromatic hydrocarbon	792	834^d	nd^x	nd^x	nd^x	tr^yx	tr^x	tr^yx	tr^zyx	0.01^zy	0.01^z	tr^zyx	tr^yx	tr^zyx
47	2-ethyl-butanal	aldehyde	797	762^d	0.02^y	0.01^y	0.01^y	0.02^y	0.03^zy	0.02^zy	0.02^y	0.02^zy	0.06^z	0.03^zy	0.02^zy	0.02^y
48	2,4-dimethyl-1-heptene	aromatic hydrocarbon	801	840^d	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
50	(E)-2-hexenal^a	aldehyde	807	846	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
51	(E)-3-hexenol	alcohol	812	844	tr^zyx	0.01^zy	0.01^z	tr^zyx	tr^zy	tr^x	nd^x	nd^x	nd^x	nd^x	nd^x	tr^x
52	2-hexenal	aldehyde	813	856^c	0.08^y	0.10^y	0.09^y	0.11^y	0.09^y	0.15^zy	0.12^zy	0.14^zy	0.22^z	0.19^zy	0.11^y	0.10^y
53	1-(2-methyl-1-cyclopenten-1-yl)-ethanone	ketone	813		tr	tr	tr	tr	tr	tr	tr	tr	0.01	tr	tr	tr
55	(Z)-3-hexenol^a	alcohol	816	850	0.22^z	0.21^z	0.23^z	0.19^z	0.18^z	0.13^zy	0.04^y	0.06^y	0.04^y	0.07^y	0.05^y	0.03^y
60	ethylbenzene^a	aromatic hydrocarbon	819	850^d	0.11^zy	0.13^zy	0.12^zy	0.15^zy	0.12^zy	0.18^z	0.06^y	0.07^y	0.10^zy	0.06^y	0.07^zy	0.05^y
61	4-methyl-octane	aromatic hydrocarbon	825	863^d	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	nd
65	hexanol^a	alcohol	832	863	1.12	0.93	0.69	0.88	1.03	0.69	0.54	0.39	0.83	0.64	0.55	0.33
70	styrene^a	other	851	893^c	0.33^zy	0.45^z	0.43^z	0.51^z	0.31^zy	0.51^z	0.02^y	0.03^y	0.02^y	0.03^y	0.02^y	0.02^y
73	2-heptanone^a	ketone	853	889	0.02	0.01	0.01	0.01	0.02	0.02	0.01	0.01	0.04	0.01	0.01	tr
75	2-butylfuran	furan	854	892^d	0.01	0.01	tr	0.01	0.01	0.02	0.01	0.01	0.03	0.02	0.01	tr
80	(Z)-4-heptenal	aldehyde	864	893	tr^y	tr^y	tr^y	tr^y	tr^y	tr^zy	tr^zy	0.01^zy	0.02^z	0.01^zy	0.01^zy	0.01^zy
82	heptanal^a	aldehyde	866	901	0.16	0.14	0.10	0.14	0.10	0.13	0.12	0.13	0.34	0.20	0.12	0.11
84	methional	sulfide	871	909^c	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
85	(E,E)-2,4-hexadienal^a	aldehyde	876	907	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
89	amyl acetate	ester	883	911	tr	tr	tr	0.01	tr	0.01	tr	tr	0.01	0.01	tr	tr
92	cumene	aromatic hydrocarbon	889	924	tr^zy	tr^z	tr^zy	tr^z	tr^zy	tr^z	nd^y	nd^y	nd^y	nd^y	nd^y	nd^y
102	4-methyl-2-heptanone	ketone	908	918	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
106	RI918	other	918		0.04^zy	0.03^zy	0.02^y	0.04^zy	0.05^zy	0.04^zy	0.03^zy	0.04^zy	0.11^z	0.05^zy	0.04^zy	0.03^zy
110	6-methyl-2-heptanone	ketone	929	955^d	0.02	0.02	0.02	0.02	0.01	0.02	0.01	0.01	0.02	0.02	0.01	0.01
111	(E)-2-heptenal^a	aldehyde	931	947	0.13	0.12	0.10	0.13	0.10	0.10	0.09	0.09	0.22	0.14	0.08	0.09
113	benzaldehyde^a	aldehyde	933	952	0.05	0.07	0.05	0.06	0.09	0.06	0.05	0.06	0.14	0.07	0.05	0.04
116	dimethyl trisulfide^a	sulfide	939	974^c	0.01	0.05	0.02	0.01	0.11	0.20	0.02	0.02	0.01	tr	0.11	tr
117	2-methyl-1-hepten-6-one	ketone	943	966^d	0.02	0.01	0.01	0.01	0.01	0.01	tr	tr	0.01	0.01	0.01	tr
118	(Z)-3-heptenol	alcohol	944	959^d	0.02	0.01	tr	tr	0.01	tr	tr	tr	tr	tr	tr	tr
119	(E)-2-heptenol^a	alcohol	948	958	tr	tr	nd	tr	tr	tr	tr	tr	tr	tr	tr	tr
121	heptanol^a	alcohol	952	959	0.15	0.11	0.06	0.09	0.09	0.07	0.06	0.05	0.15	0.09	0.06	0.04
122	3,5,5-trimethyl-2-hexene	aromatic hydrocarbon	954	968^d	tr^y	0.02^zy	0.01^zy	0.01^zy	tr^y	0.02^zy	0.01^zy	0.02^zy	0.02^z	0.02^zy	0.01^zy	0.01^y
123	1-octen-3-one	ketone	957	972	0.02	0.02	0.02	0.02	0.01	0.01	0.02	0.02	0.03	0.02	0.02	0.02
127	1-octen-3-ol	alcohol	965	974	0.42	0.50	0.41	0.54	0.39	0.47	0.35	0.34	0.72	0.51	0.35	0.32
128	phenol	phenol	968	980^c	0.08	0.05	0.05	nd	nd	nd	nd	0.02	nd	nd	nd	0.01
129	6-methyl-5-hepten-2-one^a	ketone	969	981	13.09	13.80	13.98	14.53	10.54	15.05	9.19	8.68	10.15	11.61	9.72	9.76
131	3-octanone^a	ketone	970	979	0.04	0.05	0.04	0.05	0.03	0.04	0.04	0.05	0.10	0.06	0.04	0.04
133	2-pentylfuran	furan	973	984	0.61	0.89	0.62	0.93	0.42	1.09	0.58	0.63	1.01	0.89	0.62	0.61
136	1-cyclohexyl-ethanone	ketone	978	963^d	tr	tr	0.01	0.01	tr	tr	tr	tr	tr	tr	tr	tr
137	6-methyl-5-hepten-2-ol^a	alcohol	978	989	0.05	0.04	0.06	0.09	0.04	0.07	0.02	0.02	0.02	0.04	0.02	0.02
138	(E,Z)-2,4-heptadienal,	aldehyde	980	1,000^c	0.06^zy	0.06^zy	0.05^y	0.06^zy	0.05^y	0.05^y	0.06^zy	0.07^zy	0.14^z	0.08^zy	0.04^y	0.06^zy
139	RI980	other	980		0.03^yx	0.03^yx	0.02^yx	0.01^x	0.01^x	0.04^yx	0.06^zyx	0.09^zyx	0.16^z	0.12^zy	0.05^yx	0.07^zyx
141	trans-2-(2-pentenyl)furan	furan	983	984^d	tr	0.01	0.01	0.01	tr	0.02	0.01	0.01	0.02	0.02	0.01	tr
142	hexanoic acid	acid	985	967	nd	tr	tr	tr	nd	nd	nd	nd	nd	nd	nd	nd
144	octanal^a	aldehyde	989	998	0.27	0.29	0.20	0.26	0.15	0.22	0.25	0.28	0.60	0.46	0.23	0.28
149	(E,E)-2,4-heptadienal	aldehyde	997	1,005	0.09^y	0.09^y	0.07^y	0.08^y	0.07^y	0.08^y	0.08^y	0.09^y	0.31^z	0.14^zy	0.05^y	0.07^y
152	hexyl acetate^a	ester	1,002	1,007	tr	tr	tr	0.01	tr	tr	nd	nd	nd	tr	nd	nd
154	RI1008	ketone	1,008		tr^w	tr^w	tr^w	tr^w	tr^w	0.01^xw	0.02^yxw	0.03^zyx	0.05^z	0.03^zy	0.02^yxw	0.02^yxw
155	3-ethyl-4-methylpentanol	alcohol	1,011	1,023^d	tr	tr	tr	tr	tr	tr	tr	nd	tr	tr	tr	tr
156	p-cymene	monoterpene	1,012	1,020	tr	tr	tr	tr	tr	tr	tr	tr	tr	nd	nd	nd
158	RI1018	aromatic hydrocarbon	1,017		0.01	nd	0.01	0.01	tr	0.02	tr	nd	nd	nd	tr	nd
159	limonene^a	monoterpene	1,018	1,024	0.01^zy	0.01^zy	tr^y	0.01^zy	tr^y	0.01^zy	0.01^zy	0.01^zy	0.04^z	0.02^zy	tr^zy	0.01^zy
161	(Z)-2-decene	aromatic hydrocarbon	1,020	1,009^d	0.57^zyx	0.98^z	0.84^zyx	0.86^zyx	0.61^zyx	0.91^zy	0.49^zyx	0.49^zyx	0.46^yx	0.72^zyx	0.48^yx	0.40^x
163	2-ethyl-1-hexanol^a	alcohol	1,022	1,032^c	tr^z	tr^zy	nd^y	nd^y	nd^y	nd^y	nd^y	tr^zy	nd^y	nd^y	nd^y	nd^y
165	2,2,6-trimethyl-cyclohexanone	ketone	1,023	1,036^d	tr	tr	0.01	0.01	tr	0.01	tr	tr	tr	tr	tr	tr
166	benzyl alcohol^a	alcohol	1,024	1,026	0.18	0.18	0.24	0.31	0.44	0.19	0.16	0.22	0.34	0.26	0.17	0.15
170	3-octen-2-one	ketone	1,031	1,030	nd^y	nd^y	nd^y	tr^zy	nd^y	nd^y	nd^y	nd^y	tr^z	tr^zy	tr^zy	tr^zy
172	benzeneacetaldehyde^a	aldehyde	1,033	1,036	0.02	0.03	0.03	0.04	0.02	0.03	0.01	0.02	0.03	0.03	0.01	0.02
175	RI1040	ketone	1,040		0.04	0.04	0.03	0.04	0.05	0.03	0.02	0.03	0.09	0.04	0.03	0.03
180	2,6-dimethyl-2,6-octadiene	aromatic hydrocarbon	1,047	980^d	0.03	0.04	0.04	0.04	0.02	0.03	0.02	0.02	0.02	0.03	0.02	0.03
181	bergamal	aldehyde	1,049	1,051	0.01	0.02	0.02	0.02	tr	0.01	tr	tr	tr	0.01	tr	0.01
183	(Z)-3-octenol	alcohol	1,051	1,047	0.01	0.02	0.01	0.01	0.01	0.02	tr	tr	tr	tr	tr	tr
185	RI1053	other	1,053		0.06	0.08	0.06	0.08	0.02	0.05	0.03	0.02	0.02	0.04	0.02	0.02
187	(E)-2-octenal^a	aldehyde	1,054	1,060^c	0.09	0.09	0.07	0.10	0.06	0.06	0.05	0.05	0.13	0.08	0.04	0.06
191	acetophenone	ketone	1,059	1,059	tr^zy	tr^zy	tr^zy	tr^z	tr^zy	tr^zy	tr^zy	tr^y	tr^zy	nd^y	nd^y	nd^y
192	6-methyl-3,5-heptadiene-2-one	ketone	1,061	1,105^d	tr^zyxw	tr^zyx	tr^z	tr^zy	tr^zyxw	tr^zyx	tr^xw	tr^w	tr^yxw	tr^zyxw	tr^xw	nd^w
195	(E)-2-octenol^a	alcohol	1,068	1,060	0.04	0.06	0.05	0.07	0.04	0.05	0.05	0.04	0.07	0.06	0.04	0.04
196	(E,E)-3,5-octadien-2-one	ketone	1,068	1,083^d	0.02	0.03	0.03	0.03	0.02	0.03	0.03	0.03	0.04	0.03	0.02	0.03
199	RI1072	other	1,073		0.05	0.06	0.04	0.04	0.04	0.04	0.03	0.05	0.08	0.08	0.02	0.04
200	octanol^a	alcohol	1,073	1,063	0.17	0.19	0.11	0.14	0.10	0.11	0.10	0.11	0.21	0.19	0.12	0.10
211	2-nonanone	ketone	1,095	1,087	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
217	(E)-4-nonenal	aldehyde	1,098	1,105^d	tr	0.02	0.01	0.02	0.01	0.01	0.01	0.01	0.01	0.01	tr	0.01
223	perillene	furan	1,103	1,102	0.04	0.06	0.06	0.08	0.03	0.07	0.04	0.03	0.03	0.05	0.03	0.04
227	(Z)-6-nonenal	aldehyde	1,108	1,097	0.24^x	0.43^yx	0.30^x	0.25^x	0.13^x	0.73^zyx	0.87^zyx	1.5^zy	1.16^zyx	1.67^z	0.73^zyx	1.24^zyx
228	nonanal^a	aldehyde	1,112	1,100	0.71^zy	1.04^zy	0.82^zy	0.83^zy	0.34^y	1.06^zy	1.04^zy	1.39^zy	1.28^zy	1.81^z	0.99^zy	1.48^zy
239	RI1137	other	1,137		0.16	0.15	0.10	0.16	0.14	0.13	0.08	0.10	0.29	0.16	0.10	0.11
246	RI1153	ketone	1,153		0.02	0.02	0.01	0.02	0.02	0.02	0.01	0.02	0.04	0.02	0.02	0.02
247	(E,E)-2,6-nonadienal	aldehyde	1,154	1,152^d	0.02^zy	0.03^zy	0.02^zy	0.03^zy	0.01^y	0.02^zy	0.03^zy	0.03^zy	0.04^zy	0.04^z	0.02^zy	0.03^zy
254	(E,Z)-2,6-nonadienal	aldehyde	1,166	1,150	0.54^yx	0.99^zyx	0.71^zyx	0.89^zyx	0.36^x	0.86^zyx	1.24^zyx	1.42^zy	1.28^zyx	1.65^z	0.70^zyx	1.17^zyx
256	(Z)-3-nonenol	alcohol	1,176	1,152	0.29^zyxw	0.48^z	0.46^zyx	0.48^zy	0.33^zyxw	0.34^zyxw	0.17^zyxw	0.17^xw	0.15^w	0.23^zyxw	0.20^zyxw	0.17^yxw
257	(E)-2-nonenal	aldehyde	1,177	1,157	0.25	nd	nd	nd	0.47	nd	0.59	1.29	0.68	0.94	0.82	0.80
258	(E,Z)-3,6-nonadienol	alcohol	1,178	1,149	3.77^yxw	5.97^zy	6.32^z	4.94^zyx	4.35^zyxw	4.42^zyxw	2.73^xw	2.82^xw	2.71^xw	3.21^xw	2.32^w	2.23^w
259	(E,Z)-2,6-nonadienol	alcohol	1,183	1,159	tr	0.03	0.02	0.05	tr	0.02	0.06	0.04	0.02	0.03	tr	0.02
261	(E)-2-nonenol	alcohol	1,187	1,163	0.02	0.07	0.05	0.17	0.03	0.04	0.14	0.06	0.03	0.06	0.02	0.04
263	(Z)-6-nonenol	alcohol	1,191	1,164	0.25^zyx	0.50^z	0.41^zy	0.33^zyx	0.22^yx	0.39^zyx	0.17^yx	0.24^zyx	0.22^yx	0.33^zyx	0.17^yx	0.14^x
265	nonanol^a	alcohol	1,193	1,165	1.00^zy	1.84^z	1.51^zy	1.41^zy	0.69^y	1.36^zy	0.58^y	0.63^y	0.57^y	1.02^zy	0.64^y	0.53^y
268	1-(4-methylphenyl)-ethanone	ketone	1,200	1,191^c	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
277	2,4-nonadienal	aldehyde	1,214	1,200^c	tr	0.01	tr	0.01	tr	0.01	tr	tr	0.01	0.01	tr	tr
286	decanal^a	aldehyde	1,228	1,201	0.02	0.02	0.01	0.02	0.01	0.02	0.02	0.02	0.04	0.03	0.03	0.02
293	9-decenol	alcohol	1,234	1,262^d	tr	0.01	0.01	0.02	tr	0.01	tr	tr	tr	tr	tr	tr
295	(E,E)-2,4-nonadienal	aldehyde	1,236	1,210	0.10	0.12	0.09	0.14	0.07	0.08	0.07	0.08	0.16	0.13	0.07	0.09
296	β-cyclocitral^a	aldehyde	1,238	1,217	0.01	0.02	0.02	0.02	tr	0.02	tr	tr	0.01	0.01	tr	0.01
302	2-ethylhexyl acrylate	ester	1,252	1,220^d	tr	tr	tr	tr	tr	nd	nd	nd	nd	nd	nd	tr
304	3-methyl-3-(4-methyl-3-pentenyl)-2-oxiranecarbaldehyde	aldehyde	1,254	1,236^d	0.04	0.06	0.05	0.05	0.02	0.03	0.02	0.03	0.02	0.03	0.02	0.04
309	neral	aldehyde	1,261	1,235	0.15	0.20	0.22	0.23	0.12	0.20	0.11	0.10	0.11	0.15	0.11	0.15
314	RI1268	other	1,268		tr	tr	tr	tr	tr	tr	0.03	0.02	0.05	0.02	0.02	0.02
316	1,3-bis(1,1-dimethylethyl)-benzene	aromatic hydrocarbon	1,272	1,249^d	0.02	0.02	0.02	0.03	0.01	0.03	tr	tr	tr	tr	tr	tr
317	geraniol^a	alcohol	1,277	1,249	tr	0.01	0.01	0.01	tr	tr	tr	tr	tr	tr	tr	tr
319	(E)-2-decenal	aldehyde	1,288	1,260	0.04	0.04	0.03	0.04	0.02	0.02	0.02	0.02	0.04	0.03	0.01	0.02
322	geranial	aldehyde	1,294	1,264	0.34	0.43	0.45	0.47	0.25	0.39	0.22	0.21	0.23	0.31	0.24	0.31
329	decanol	alcohol	1,301	1,266	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
339	(E)-2,7-octadien-1-yl acetate	ester	1,323	1,388^d	0.01	0.02	0.02	0.06	tr	0.02	0.02	tr	tr	tr	tr	0.01
342	4-ethyl-2-hexynal	aldehyde	1,328		0.02	0.05	0.05	0.09	0.01	0.02	0.02	0.01	0.01	0.02	tr	0.01
345	undecanal	aldehyde	1,338	1,305	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
349	(E,E)-2,4-decadienal	aldehyde	1,346	1,315	0.01	0.01	tr	0.01	tr	tr	tr	tr	0.03	0.01	tr	0.01
358	γ-nonalactone	lactone	1,386	1,358	0.03^zy	0.06^zy	0.07^zy	0.09^z	0.04^zy	0.04^zy	0.02^y	0.02^y	0.02^y	0.03^zy	0.02^y	0.01^y
359	(E)-2-undecenal	aldehyde	1,395	1,357	0.01	0.01	0.01	0.02	tr	tr	tr	tr	0.02	0.01	tr	tr
374	geranyl acetone^a	ketone	1,478	1,453	1.21	1.44	1.27	1.54	0.84	1.67	0.98	1.02	1.20	1.28	0.95	1.20
377	(E)-β-ionone	ketone	1,505	1,487	0.02	0.02	0.02	0.03	0.01	0.02	0.01	0.01	0.01	0.01	0.01	0.01
380	β-ionone epoxide	epoxide	1,507	1,473^d	0.02	0.02	0.02	0.03	0.01	0.02	0.01	0.01	0.02	0.02	0.01	0.02
391	trans-ψ-ionone	ketone	1,601	1,589^d	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr	tr
The volatile relative content was determined by normalizing the areas of the compound peaks to that of the internal standard. Mean values were obtained from three biological replicates for each grafting combination. Retention indices (RI) were calculated using a standard mixture of alkanes ranging from C₈ to C₂₀. The abbreviation 'RI' stands for retention index; 'tr' indicates that the peak was detected, but the value was below 0.0095; 'nd' denotes that the compound was not detected. ^aCompounds were identified using authentic volatile standards. ^bPublished RI for the DB-5 column, unless otherwise stated, were sourced from Adams^[32]. ^cPublished RI on DB-5 column reported on Flavornet and Human Odor Space^[58]. ^dPublished RI on DB-5 column reported on PubChem^[59]. ^z−wDifferent letters in the same rows indicate significant differences according to Tukey's Honestly Significant Difference test at p < 0.05.

Table 3.

Volatile compounds of 'Ningnongke huadai' watermelon grafted onto different rootstocks.

Class	NG	Type
		Wild watermelon			Bottle gourd		Pumpkin
		NZ101	YS	YZ1	JX1	SZ111	JC	MX	QY1	ZS	JX2	NZ1
Acid	0	1	1	1	0	0	0	0	0	0	0	0
Alcohol	28	28	25	27	27	27	26	26	26	26	25	27
Aldehyde	35	34	34	34	35	34	35	35	35	35	35	35
Aromatic hydrocarbon	10	9	10	11	11	11	10	9	9	9	10	8
Epoxide	1	1	1	1	1	1	1	1	1	1	1	1
Ester	5	5	5	5	5	4	3	3	3	4	3	4
Furan	4	4	4	4	4	4	4	4	4	4	4	4
Ketone	22	22	22	23	22	22	22	22	23	22	22	21
Lactone	1	1	1	1	1	1	1	1	1	1	1	1
Monoterpene	2	2	2	2	2	2	2	2	2	1	1	1
Other	7	7	7	7	7	7	7	7	7	7	7	7
Phenol	1	1	1	0	0	0	0	1	0	0	0	1
Sulfide	3	3	3	3	3	3	3	3	3	3	3	3
Total	119	118	116	119	118	116	114	114	114	113	112	113

Table 4.

Total number of volatile compounds in each chemical class in watermelon grafted onto different rootstocks.

Class	NG	Type
		Wild watermelon			Bottle gourd		Pumpkin
		NZ101	YS	YZ1	JX1	SZ111	JC	MX	QY1	ZS	JX2	NZ1
Acid	0	0.01	0	0	0	0	0	0	0	0	0	0
Alcohol	8.19^abcd	11.55^a	10.99^ab	10.16^abc	8.33^abcd	8.73^abcd	5.46^bcd	5.47^bcd	6.54^abcd	7.09^abcd	4.96^cd	4.44^d
Aldehyde	6.49	7.45	5.71	6.77	5.23	7.41	8.17	10.22	12.9	12.37	7.36	9.08
Aromatic hydrocarbon	0.77^ab	1.2^a	1.07^ab	1.12^a	0.79^ab	1.2^a	0.6^ab	0.62^ab	0.63^ab	0.85^ab	0.6^ab	0.51^b
Epoxide	0.02	0.02	0.02	0.03	0.01	0.02	0.01	0.01	0.02	0.02	0.01	0.02
Ester	0.03	0.04	0.04	0.1	0.02	0.04	0.03	0.02	0.02	0.03	0.01	0.02
Furan	0.67	0.97	0.71	1.03	0.46	1.19	0.64	0.69	1.09	0.97	0.68	0.66
Ketone	14.6	15.54	15.5	16.39	11.64	17	10.39	9.95	11.88	13.23	10.9	11.21
Lactone	0.03^ab	0.06^ab	0.07^ab	0.09^a	0.04^ab	0.04^ab	0.02^b	0.02^b	0.02^b	0.03^ab	0.02^b	0.01^b
Monoterpene	0.01	0.01	0.01	0.01	0.02	0.01	0.01	0.01	0.04	0.02	0.01	0.01
Other	0.66	0.81	0.67	0.84	0.57	0.81	0.28	0.35	0.72	0.49	0.28	0.32
Phenol	0.08	0.05	0.05	0	0	0	0	0.02	0	0	0	0.01
Sulfide	0.03	0.11	0.06	0.04	0.33	0.6	0.04	0.06	0.04	0.02	0.3	0.01
Total	31.58	37.82	34.9	36.58	27.44	37.06	25.66	27.44	33.91	35.12	25.13	26.32
The relative content data are presented as the mean based on three biological replicates. In the same row, differing letters indicate a statistically significant difference as determined by Tukey's Honestly Significant Difference test (p < 0.05).

Table 5.

Total relative content of volatile compounds in each chemical class in watermelon grafted onto different rootstocks.

Code	Compound	Class	NG	Wild watermelon	Bottle gourd	Pumpkin
3	2-methyl-1-butanol	alcohol	0.14a	0.1a	0.12a	0.05b
43	propyl-cyclopentane	aromatic hydrocarbon	nd b	tr b	tr b	0.01a
48	2,4-dimethyl-1-heptene	aromatic hydrocarbon	tr b	tr b	tr b	0.01a
51	(E)-3-hexenol	alcohol	0.01ab	0.01a	tr bc	tr c
55	(Z)-3-hexenol	alcohol	0.22ab	0.21a	0.16b	0.05c
65	hexanol	alcohol	1.12a	0.83ab	0.86ab	0.55b
70	styrene	other	0.33a	0.46a	0.41a	0.02b
92	cumene	aromatic hydrocarbon	tr a	0.01a	tr a	nd b
117	2-methyl-1-hepten-6-one	ketone	0.02a	0.01ab	0.01ab	0.01b
118	(Z)-3-heptenol	alcohol	0.02a	0.01ab	0.01ab	tr b
128	phenol	phenol	0.08a	0.03ab	nd b	0.01b
154	RI1008	ketone	tr b	tr b	0.01b	0.03a
161	(Z)-2-decene	aromatic hydrocarbon	0.57bc	0.89a	0.76ab	0.5c
163	2-ethyl-1-hexanol	alcohol	0.01a	tr b	nd b	tr b
191	acetophenone	ketone	tr b	tr a	tr b	tr b
192	6-methyl-3,5-heptadiene-2-one	ketone	tr bc	tr a	tr ab	tr c
227	(Z)-6-nonenal	aldehyde	0.24b	0.33b	0.43b	1.2a
254	(E,Z)-2,6-nonadienal	aldehyde	0.54b	0.86ab	0.61b	1.24a
256	(Z)-3-nonenol	alcohol	0.29bc	0.47a	0.34b	0.18c
258	(E,Z)-3,6-nonadienol	alcohol	3.77bc	5.74a	4.39b	2.67c
358	γ-nonalactone	lactone	0.03b	0.07a	0.04b	0.02b
The relative volatile content was quantified by normalizing the peak area of each compound to the peak area of the internal standard. The values represent the mean of three biological replicates per type. The notation 'tr' indicates a detected peak with a value below 0.0095, while 'nd' signifies not detected. Variations in letters within the same rows denote statistically significant differences as determined by Tukey's Honestly Significant Difference test (p < 0.05).

Table 6.

Differentially accumulated volatile compounds identified in watermelon grafted onto each rootstock type compared to NG.

Code	Compound	Class	PC1	PC2
70	styrene	other	0.94
92	cumene	aromatic hydrocarbon	0.91
256	(Z)-3-nonenol	alcohol	0.90
55	(Z)-3-hexenol	alcohol	0.90
51	(E)-3-hexenol	alcohol	0.89
316	1,3-bis(1,1-dimethylethyl)- benzene	aromatic hydrocarbon	0.87
183	(Z)-3-octenol	alcohol	0.87
154	RI1008	ketone	0.86
139	RI980	other	0.81
258	(Z,Z)-3,6-nonadienol	alcohol	0.81
43	propylcyclopentane	aromatic hydrocarbon	0.80
80	(Z)-4-heptenal	aldehyde	0.80
48	2,4-dimethyl-1-heptene	aromatic hydrocarbon	0.78
38	2,4-dimethyl-heptane	aromatic hydrocarbon	0.78
358	γ-nonalactone	lactone	0.77
122	3,5,5-trimethyl-2-hexene	aromatic hydrocarbon		0.66
20	(Z)-2-pentenol	alcohol		0.61
13	(E)-2-pentenal	aldehyde		0.60
149	(E,E)-2,4-heptadienal	aldehyde		0.52
263	(Z)-6-nonenol	alcohol		0.45
52	2-hexenal	aldehyde		0.43
247	(E,E)-2,6-nonadienal	aldehyde		0.43
138	(E,Z)-2,4-heptadienal	aldehyde		0.42

Table 7.

Volatile compounds with high contribution to the PC1 and PC2 in Fig. 1d.