Rapid non-destructive testing of smooth bromegrass (<i>Bromus inermis</i>) seed vigour using multispectral imaging

Shuangfeng Yang; Shuheng Zhang; Kun Yi; Kai Wei; Hanguo Zeng; Zhicheng Jia; Peisheng Mao; Xu Han; Manli Li; Shuangfeng Yang; Shuheng Zhang; Kun Yi; Kai Wei; Hanguo Zeng; Zhicheng Jia; Peisheng Mao; Xu Han; Manli Li

doi:10.48130/GR-2023-0012

Figures (4) Tables (4)

Figure 1.
Germination situation of smooth bromegrass seeds under different conditions. Data in (a) and (b) were the germination potential and germination percentage of smooth bromegrass seeds at different maturity levels and harvest years under standard germination test, respectively. Data in (c) and (d) were the germination percentage of smooth bromegrass seeds at different maturity levels and harvest years after artificial accelerated aging, respectively. Different lowercase letters represent significant difference between different treatments during the experimental period (p < 0.05). Bars represent the mean values of four replicates ± standard deviation (SD).
Figure 2.
Chlorophyll a and chlorophyll b fluorescence intensity of smooth bromegrass seeds at different maturity levels and harvest years. Data in (a) and (b) were chlorophyll a fluorescence intensity of seeds at different maturity levels and harvest years, respectively. Data in (c) and (d) were chlorophyll b fluorescence intensity of seeds at different maturity levels and harvest years, respectively. Different lowercase letters represent significant difference between different treatments during the experimental period (p < 0.05). Bars represent the mean values of four replicates ± SD.
Figure 3.
Mean spectral reflectance of smooth bromegrass seeds at (a) different maturity levels and (b) harvest years.
Figure 4.
Multivariate analysis based on multispectral data of smooth bromegrass seeds. Principal component analysis of smooth bromegrass seeds at (a) different maturity levels and (b) harvest years. LDA model diagram of smooth bromegrass seeds at (c) different maturity levels and (d) harvest years.

Characteristic	Different maturity			Different harvest years
Characteristic	Milk-ripening stage	Wax-ripening stage	Full-ripening stage	2019	2017	2014
Area (mm²)	12.61 ± 2.095c	12.89 ± 1.777b	13.45 ± 1.668a	15.87 ± 2.675b	17.74 ± 2.845a	16.14 ± 2.512b
Length (mm)	9.87 ± 0.901a	9.65 ± 0.904b	9.89 ± 0.744a	12.55 ± 1.793b	13.44 ± 2.004a	12.58 ± 1.843b
Width (mm)	1.81 ± 0.278c	1.90 ± 0.211b	2.02 ± 0.212a	2.19 ± 0.282b	2.31 ± 0.283a	2.16 ± 0.253b
Length-width ratio	0.18 ± 0.029c	0.20 ± 0.024b	0.20 ± 0.022a	0.18 ± 0.029	0.17 ± 0.027	0.18 ± 0.039
Compactness Circle	0.18 ± 0.028c	0.19 ± 0.023b	0.20 ± 0.019a	0.17 ± 0.025a	0.17 ± 0.021b	0.18 ± 0.036a
Compactness Ellipse	0.99 ± 0.008b	0.99 ± 0.006a	0.99 ± 0.008b	0.96 ± 0.029b	0.96 ± 0.025b	0.97 ± 0.022a
BetaShape_a	1.73 ± 0.221c	1.79 ± 0.182b	1.92 ± 0.237a	3.30 ± 1.878	3.33 ± 2.059	3.07 ± 1.415
BetaShape_b	1.58 ± 0.199c	1.69 ± 0.174b	1.78 ± 0.208a	2.74 ± 1.169	2.75 ± 1.032	2.61 ± 0.847
Vertical Skewness	−0.07 ± 0.051c	−0.04 ± 0.034a	−0.06 ± 0.046b	−0.10 ± 0.088	−0.09 ± 0.076	−0.09 ± 0.07
CIELab L*	46.28 ± 2.959b	44.72 ± 3.395c	47.06 ± 2.306a	51.43 ± 2.578a	51.06 ± 2.442b	48.42 ± 2.047c
CIELab A*	6.17 ± 1.402b	4.96 ± 1.443c	7.94 ± 0.787a	6.26 ± 0.73b	7.71 ± 0.847a	7.67 ± 0.823a
CIELab B*	17.78 ± 1.682b	12.58 ± 3.04c	18.58 ± 1.32a	17.57 ± 1.658c	20.18 ± 1.56a	19.68 ± 1.879b
Saturation	19.06 ± 1.844b	13.50 ± 3.132c	20.66 ± 1.392a	18.80 ± 1.738c	21.79 ± 1.674a	21.33 ± 1.932b
Hue	1.23 ± 0.066a	1.17 ± 0.112b	1.17 ± 0.03b	1.23 ± 0.033a	1.21 ± 0.028b	1.19 ± 0.109c
Note: Different lowercase letters in the same line indicate significant differences, while the same letters indicate no significant differences (p < 0.05). The number of repetitions for this experiment was n = 4 for each seed lot samples.

Table 1.

Comparative analysis of morphological characteristics of smooth bromegrass seeds with different maturity levels and different harvest years.

Model	Index	Different maturity			Different harvest year
Model	Index	M vs W	W vs F	M vs F	2014 vs 2017	2017 vs 2019	2014 vs 2019
LDA	Sensitivity (%)	96.6	99.2	99.2	91.6	98.3	96.6
	Specificity (%)	91.7	99.2	100.0	88.4	100.0	98.3
	Precision (%)	92.0	99.2	100.0	88.6	100.0	98.3
	Accuracy (%)	94.2	99.2	99.6	90.0	99.2	97.5
SVM	Sensitivity (%)	95.8	98.3	100.0	89.9	96.6	95.0
	Specificity (%)	91.7	97.5	98.3	82.6	95.9	95.0
	Precision (%)	91.9	97.5	98.3	83.6	95.8	95.0
	Accuracy (%)	93.8	97.9	99.2	86.3	96.3	95.0
RF	Sensitivity (%)	85.7	98.3	97.5	81.5	89.9	89.1
	Specificity (%)	89.3	98.3	96.7	74.4	88.4	82.6
	Precision (%)	88.7	98.3	96.7	75.8	88.4	83.5
	Accuracy (%)	87.5	98.3	97.1	77.9	89.2	85.8
Note: M stands for milk-ripening stage, W stands for wax-ripening stage and F stands for full-ripening stage.

Table 2.

Prediction of smooth bromegrass seeds with different maturity levels and harvested in different harvest years by LDA, SVM and RF models.

Sample	Classification	Actual number of CCS	Correctly predicted number of CCS	Actual number of RSS	Correctly predicted number of RSS	Accuracy of prediction (%)
Maturity level	D	301	247	899	877	93.7%
	F	7	5	1193	1165	97.5%
	A	109	70	1091	1095	97.1%
	N	783	769	417	324	91.1%
	A + N	892	811	308	218	85.8%
Harvest year	D	766	691	434	404	91.3%
	F	3	3	1197	1176	98.3%
	A	12	9	1188	1102	92.6%
	N	419	390	781	705	91.3%
	A + N	431	386	769	742	94.0%
Note: CCS stands for Corresponding classification samples, RSS stands for Remaining sorted samples. N stands for normal seedlings, A stands for abnormal seedlings, F stands for fresh ungerminated seeds and D stands for dead seeds.

Table 3.

Germination prediction of smooth bromegrass seeds with different maturity levels and harvest years based on nCDA.

Model	Index	Different maturity				Different harvest years
Model	Index	N	A	F	D	N	A	F	D
LDA	Sensitivity (%)	79.9	0	0	12.4	88.4	0	0	96.5
	Specificity (%)	40.5	99.7	99.7	94.5	96.5	99.2	99.2	87.1
	Precision (%)	72.6	0	0	42.3	93.4	0	0	92.8
	Accuracy (%)	66.7	91.7	98.9	74.2	93.6	98.3	98.3	93.1
SVM	Sensitivity (%)	80.8	0	0	0	86.0	0	0	97.4
	Specificity (%)	40.5	100.0	100.0	100.0	97.0	100.0	100.0	84.1
	Precision (%)	72.8	NA	NA	NA	94.1	NA	NA	91.4
	Accuracy (%)	67.2	91.9	99.2	75.3	93.1	99.2	99.2	92.5
RF	Sensitivity (%)	79.1	0	0	12.4	69.0	0	0	93.0
	Specificity (%)	39.7	99.7	100.0	95.6	93.1	100.0	100.0	72.0
	Precision (%)	72.1	0	NA	47.8	84.8	NA	NA	85.1
	Accuracy (%)	65.8	91.7	99.2	75.0	84.4	99.2	99.2	85.3
Note: N stands for normal seedlings, A stands for abnormal seedlings, F stands for fresh ungerminated seeds and D stands for dead seeds.

Table 4.

Germination prediction of smooth bromegrass seeds with different maturity levels and harvested in different years by LDA, SVM and RF models.