Variation in qualitative traits among the genotypes at the germination stage
Figure 2 presents the frequency distributions of variations in qualitative traits examined during the germination stage. Hypocotyl colour at 10 days of germination was greenish purple (59.63%) followed by green (23.85%) and purple16.51%. For seedling vigour, medium was the most frequently observed phenotype class (69.72%), followed by vigorous 25.69% and poor 4.59%.
Variation in the inflorescence traits
During this stage, mung bean genotypes under study were observed and documented for the following qualitative traits: Length of the peduncle, raceme position, calyx colour, corolla colour, leafiness (Fig. 3). Length of the peduncle was long with the mean frequency of (42.20%) while short peduncle (22.94%) was the least observed trait on the studied mung bean genotypes. For raceme position, intermediate raceme position was observed in 77.98%, followed by above the canopy type (16.51%) and pods not visible (5.50%). Most genotypes (77.98%) showed the greenish-purple colour of calyx on the flower at the flowering stage. The corolla colour was greenish yellow, light yellow, and deep yellow, and the maximum genotypes 64.22% had greenish yellow. Leafiness during the flowering period for the majority of genotypes was sparse (55.05%), while other genotypes were medium (26.61%) and abundant (18.35%).
Variation of vegetative traits
In the vegetative stage, traits such as terminal leaflet shape, terminal leaf length, leaf colour, petiole colour, petiole length, leaf senescence and growth habit were recorded (Fig. 4). Terminal leaflet shape for most of the genotypes had cuneate shape (93.02%) and ovate (6.98%). For terminal leaflet length, large was observed in 66.67%, followed by medium (29.46%) and small (3.88%). Leaf colour was dominated by green (72.09%) followed by dark green (27.91%) among studied genotypes. For petiole colour, greenish purple was the most frequently observed phenotype class (74.42%), followed by green 20.16% and purple 5.43%. The medium (58.91%) and short (34.88%) petiole length were prominent whereas 6.20% were long among studied genotypes. Variation was also noticed for leaf senescence, intermediate (65.89%) and not visibly senescent (30.23%) were prominent, while few (3.88%) were conspicuously concurrent. Erect growth type was predominant (51.16%) over semierect (41.86%) and spreading (6.98%).
Variation in the pod traits
At this stage, all the genotypes showed variations in pod traits such as pod colour, colour of ventral suture of immature pod, shape of the ripe pod, attachment of mature pod peduncle, pod pubescence, and constriction of pod between seeds (Fig. 5). Light green immature pod (63.30%) was the most frequent trait, followed by deep green (36.70%). There was variation in the colour of ventral suture of immature pod with a maximum purple colour (77.06%). The genotypes produced pods of several colours at the maturity stage, including straw, tan, and brown, and there was a greater frequency of those with black pods (51.38%). Attachment of mature pod peduncle to the angle of around 90° was observed at pod filling in 72.48% of genotypes, whereas few (3.67%) genotypes showed pendant type of attachment. The heavily (66.03%) and intermediate pubescence (32.11%) were prominent, whereas few (1.83%) were glabrous. Around 61.47% of the genotypes showed pod constriction at the pod-filling stage, which is the critical attribute of the legume crop.
Variation of maturity traits
Lodging, shattering in the field and growth patterns were the qualitative traits monitored at this growth stage. Figure 6 shows the frequency distribution of genotypes for each trait variation. Lodging of 109 genotypes was intermediate, none and heavy. Intermediate (42.64%) and none lodging (30.23%) were more frequent in most genotypes. 1% of the genotypes under study exhibited field shattering, whereas the remaining (99%) percent showed no shattering ability. More than 78.29% of genotypes had determinate growth pattern whereas 21.71% were indeterminate.
Variation of seed traits
Freshly harvested seeds had wide range of colours such as yellow, greenish yellow, light green, dark green and mixed in Fig. 7. However, light green (50.46%) and dark green (33.03%) were predominant colour. The phenotypic class mottling on the seed surface was not observed on 61.47% of mung bean genotypes, while light and medium phenotypic classes were observed on around 37.78% and 2.75% of mung bean genotypes under study. Genotypes with dull lustre on seed surface were more frequent (94.50%) compared with shiny (5.50%) lustre. Variation was also noticed for seed shape, drum and oval shaped seeds were more prominent, while 18.35% were round seed shape. Genotypes with non-concave hilum were relatively more frequent (83.49%) than those with concave (16.51%).
Powdery mildew disease incidence and severity
A total of 108 mung bean genotypes including three checks were screened for powdery mildew resistance. The susceptibility of the genotypes to powdery mildew differed, 78 genotypes were categorized as moderately susceptible, 17 were susceptible, 13 moderately resistant, one highly susceptible, and two were highly resistant to the powdery mildew in Fig. 8.
Descriptive analysis and genetic parameters of quantitative traits of mung bean genotypes
The evaluation encompassed 13 quantitative traits in mung bean genotypes. Descriptive statistics unveiled considerable variations in mung bean genotypes (Table 1). Plant height was a highly variable trait ranging from 23.46 to 94.94 cm for G16 and C3 genotypes, respectively, with a mean of 43.02 cm. The number of branches per plant exhibited the least variability, ranging from 0.73 (G9) to 5.55 (C3), with an average of 2.36 branches. Days to flowering ranged from 33 (G68) to 42 (G32) days, with an average of 38 days. Some of the genotypes matured after 62 days (minimum days to maturity by G9), while some genotypes were found to be maturing late (74 days by G32). The weight of 1000 seeds ranged from 25.23 to 82.21 g for G33 and G3 genotypes, respectively, with an average of 45.12 g. Pod length also varied from 4.21 (G28) to 9.11 (G62) cm, with an average of 6.1 cm. A considerable variation was observed for the length of the branch, number of clusters, pods weight, number of seeds per pod, seed weight and shelling percent (Table 1).
The statistical parameters related to breeding values were investigated and the outcomes are detailed in Table 1. Genetic variability studies were computed using the phenotypic coefficient of variation (PCV), genotypic coefficient of variation (GCV), heritability in broad sense (H2) and genetic advance as percentage of mean (GAM) were estimated for 13 traits. The PCV exceeded the GCV for all the traits with minor differences in the case of days to maturity, pod length, weight of 1000 seeds and days to flowering. All traits had high PCV (> 20%) except for length of the branch, pod length, and number of seed per pods where PCV was intermediate (10–20%). Low PCV (0–10%) was also observed for days to 50% flowering and days to maturity. The estimation of GCV in relation to PCV potentially help in determining the degree of genetic variation. From the study, the estimate for GCV ranged from 3% for days to maturity to 52.05% number of pods per plant. The value for PCV ranged from 3.05% for days to maturity to 57.95% seed weight.
All the studied traits reflected high heritability while lowest value of heritability (82.6%) was observed for a number of clusters and the highest value of heritability value (97.35%) for weight of 1000 seeds (Table 1). In terms of genetic advance as a percentage of the mean (GAM), most of the traits were observed with high GAM (> 20) except for days to 50% flowering and Days to maturity which showed intermediate (12.81%) and low (6.07%), respectively in Table 1.
Taking into account H2 estimates with GAM is essential for discerning gene action, as breeders rely on both values for trait improvement. High H2 associated with GAM was evident for in all traits except days to maturity and days to flowering, which displayed low and medium GAM, respectively.
Table 1
Descriptive analysis, genetic variability and heritability values of quantitative traits of mung bean genotypes across two cropping seasons in Tanzania
Trait
|
Mean ± SE
|
Range
|
GCV
|
PCV
|
H2
|
GAM
|
Min
|
Max
|
Length of the branch (cm)
|
28.72 ± 0.46
|
14.43(G25)
|
39.63(G9)
|
14.35
|
16.31
|
77.89
|
26.41
|
Number of branches per plant
|
02.36 ± 0.11
|
0.73(G9)
|
05.55(C3)
|
37.11
|
41.69
|
79.93
|
68.64
|
Number of clusters
|
10.13 ± 0.41
|
06.90(G83)
|
76.57(C3)
|
34.06
|
37.50
|
82.60
|
64.07
|
Number of pods per plant
|
30.08 ± 1.49
|
03.13(G99)
|
23.85(G73)
|
52.05
|
53.31
|
95.27
|
104.83
|
Pod length (cm)
|
06.10 ± 0.09
|
04.21(G28)
|
9.11(G62)
|
15.21
|
15.54
|
95.78
|
30.70
|
Plant height (cm)
|
43.02 ± 1.20
|
23.46(G16)
|
94.94(C3)
|
25.31
|
26.99
|
88.18
|
48.97
|
Pod weight (g)
|
18.94 ± 1.02
|
03.29(G103)
|
46.80(C3)
|
50.61
|
57.11
|
79.37
|
93.60
|
Number of seeds per pod
|
09.62 ± 0.15
|
04.99(G73)
|
12.63(G92)
|
15.00
|
16.40
|
83.50
|
28.37
|
Seed weight (g)
|
11.35 ± 0.66
|
01.43(G50)
|
36.73(C3)
|
47.77
|
57.95
|
68.80
|
82.24
|
Weight of 1000 seeds (g)
|
45.12 ± 1.14
|
25.23(G33)
|
82.21(G3)
|
25.44
|
25.78
|
97.35
|
51.80
|
Days to 50% flowering
|
38.00 ± 0.25
|
33.03(G68)
|
42.20(G32)
|
06.55
|
06.93
|
88.39
|
12.81
|
Days to maturity
|
65.53 ± 0.19
|
62.00(G9)
|
74.00(G32)
|
03.00
|
03.05
|
96.46
|
06.07
|
Shelling percent
|
61.99 ± 1.51
|
31.25(G118)
|
93.11(G59)
|
22.22
|
24.21
|
83.49
|
42.12
|
GCV; Genotypic Coefficient of Variation. PCV; Phenotypic coefficient of variation: GAM Genetic advance over percent mean H2: Heritability in a broad sense
Analysis of variance of the quantitative traits across the two cropping seasons
The combined analysis of variance of the quantitative traits revealed significant differences (p < 0.001) in all the traits (Table 2). All the traits, except for the number of branches per plant, number of pods per plant and weight of 1000 seed, showed substantial cropping season effects. Additionally, length of the branch and the number of branches per plant were significantly impacted by block effects. Significant differences among the genotypes were observed as shown in Table 2 for all traits. Exceptionally, the number of clusters and days to flowering showed no significant difference among the genotypes (p > 0.05). It was figured out that there are significant differences (p < 0.001) between checks for all the analysed traits (Table 3), with the exception of number of seeds per pod and shelling percent. The selected characteristics also significantly differed between checks and genotypes, except for number of seed per pods, day to flowering and days to maturity.
Table 2
Combined analysis of variance and sum of squares for the selected quantitative traits across two cropping seasons
Traits
|
Model (ANOVA)
|
Block effect
|
Seasonal effect
|
DF
|
sum squares
|
mean squares
|
F
|
Pr > F
|
DF
|
sum squares
|
mean squares
|
F
|
Pr(> F)
|
DF
|
sum squares
|
mean squares
|
F
|
p
|
Length of the branch (cm)
|
110
|
4735.6
|
43.05
|
16.48
|
< 0.001
|
9
|
73.7
|
8.19
|
3.58
|
< 0.001
|
1
|
39.9
|
39.9
|
15.29
|
< 0.001
|
Number of branches per plant
|
110
|
452.75
|
4.12
|
36.75
|
< 0.001
|
9
|
2.07
|
0.23
|
2.18
|
< 0.001
|
1
|
0.13
|
0.13
|
1.16
|
0.28
|
Number of clusters
|
110
|
5516
|
50.15
|
3.32
|
< 0.001
|
9
|
31.3
|
3.47
|
0.22
|
0.99
|
1
|
1433.5
|
1433.5
|
94.93
|
< 0.001
|
Number of pods per plant
|
110
|
42878
|
389.8
|
3.07
|
< 0.001
|
9
|
71
|
7.89
|
0.06
|
1
|
1
|
14.53
|
14.53
|
0.11
|
0.74
|
Pod length (cm)
|
110
|
191.43
|
1.74
|
20.15
|
< 0.001
|
9
|
0.521
|
0.06
|
0.66
|
0.75
|
1
|
4.14
|
4.14
|
47.96
|
< 0.001
|
Plant height (cm)
|
110
|
71673
|
651.57
|
7.3
|
< 0.001
|
9
|
153
|
17
|
0.18
|
1
|
1
|
1651.6
|
1651.6
|
18.51
|
< 0.001
|
Pod weight (g)
|
110
|
314545
|
285.95
|
4.2
|
< 0.001
|
9
|
337.7
|
37.52
|
0.54
|
0.85
|
1
|
1256.6
|
1256.6
|
18.43
|
< 0.001
|
Number of seeds per pod
|
110
|
387.6
|
3.52
|
2.91
|
< 0.001
|
9
|
2.54
|
0.28
|
0.22
|
0.99
|
1
|
110.2
|
110.2
|
91.11
|
< 0.001
|
Seed weight (g)
|
110
|
183964
|
167.24
|
4.59
|
< 0.001
|
9
|
194.2
|
21.58
|
0.58
|
0.81
|
1
|
138.03
|
138.03
|
3.79
|
0.05
|
Weight of 1000 seeds (g)
|
110
|
51820
|
471.09
|
11.83
|
< 0.001
|
9
|
78
|
8.69
|
0.21
|
0.99
|
1
|
131.1
|
131.1
|
3.29
|
0.07
|
Days to flowering
|
110
|
1167.74
|
10.62
|
2.81
|
< 0.001
|
9
|
7.93
|
0.88
|
0.22
|
0.99
|
1
|
800.36
|
800.36
|
211.9
|
< 0.001
|
Days to maturity
|
110
|
956.6
|
8.7
|
12.42
|
< 0.001
|
9
|
2
|
0.22
|
0.31
|
0.97
|
1
|
378
|
378
|
540
|
< 0.001
|
Shelling percent
|
110
|
53375
|
485.23
|
2.85
|
< 0.001
|
9
|
235
|
26.15
|
0.15
|
1
|
1
|
2870.1
|
2870.1
|
16.87
|
< 0.001
|
Significantly different among genotypes at p < 0.001 |
Table 3
Combining analysis of the interactions and differences between genotypes and checks for the selected quantitative traits across two cropping seasons
Contrast (Differences)
|
Traits
|
Among Genotypes (108)
|
Among Checks (2)
|
Checks vs Genotypes (1)
|
sum squares
|
mean squares
|
F
|
Pr > F
|
sum squares
|
mean squares
|
F
|
Pr(> F)
|
sum squares
|
mean squares
|
F
|
p
|
Length of branch (cm)
|
4508
|
41.71
|
16.49
|
< 0.001
|
20
|
10.22
|
4.04
|
0.0195
|
54
|
54.4
|
21.5
|
< 0.001
|
Number of branches per plant
|
202.9
|
1.88
|
17.83
|
< 0.001
|
242.2
|
121.12
|
1149.75
|
< 0.001
|
7.5
|
7.51
|
71.32
|
< 0.001
|
Number of clusters
|
2301
|
21.3
|
0.857
|
0.8
|
3030
|
1515
|
60.94
|
< 0.001
|
660
|
660
|
26.55
|
< 0.001
|
Number of pods per plant
|
34849
|
322.7
|
2.422
|
< 0.001
|
3834
|
1917.2
|
14.39
|
< 0.001
|
736
|
736
|
5.52
|
0.02
|
Pod length (cm)
|
161.91
|
1.499
|
13.15
|
< 0.001
|
8.65
|
4.323
|
37.92
|
< 0.001
|
8.55
|
8.55
|
75.03
|
< 0.001
|
Plant height (cm)
|
2246
|
208
|
2.011
|
< 0.001
|
47956
|
23978
|
231.84
|
< 0.001
|
7410
|
7410
|
71.65
|
< 0.001
|
Pod weight (g)
|
16962
|
157
|
2.026
|
< 0.001
|
11775
|
5888
|
75.94
|
< 0.001
|
3052
|
3052
|
39.3
|
< 0.001
|
Number of seeds per pod
|
329.7
|
3.053
|
1.556
|
0.01
|
11.7
|
5.84
|
2.98
|
0.054
|
3.2
|
3.18
|
1.62
|
0.21
|
Seed weight (g)
|
11259
|
104.3
|
2.75
|
< 0.001
|
6191
|
3095.6
|
81.65
|
< 0.001
|
5832
|
5832
|
153.8
|
< 0.001
|
Weight of 1000 seeds (g)
|
24836
|
230
|
5.45
|
< 0.001
|
25983
|
12992
|
307.9
|
< 0.001
|
2028
|
2028
|
48.06
|
< 0.001
|
Days to flowering
|
497.7
|
4.61
|
0.509
|
1
|
164
|
82.02
|
9.06
|
< 0.001
|
0.7
|
0.7
|
0.08
|
0.78
|
Days to maturity
|
734.7
|
6.8
|
2.162
|
< 0.001
|
125
|
62.52
|
19.87
|
< 0.001
|
5.1
|
5.07
|
1.61
|
0.21
|
Shelling percent
|
41199
|
381.5
|
1.949
|
< 0.001
|
752
|
376.1
|
1.922
|
0.15
|
22572
|
22572
|
115.3
|
< 0.001
|
Significantly different among genotypes at p < 0.001 |
Principal component analysis of the quantitative traits of mung bean genotypes
The quantitative traits of the genotypes of mung beans were grouped into four main components using principal component analysis (PCA). The first four components with eigenvalues greater than one (> 1), collectively explained 59.77% of the variation. While eigenvalues (˂ 1) were observed for PCs 5–13. The PC1 contributed 27.45% variation, was predominantly associated with yield and its related traits (seed weight, pods weight, pods per plants and number of branches) (Table 4). In contrast, the PC2 was significantly influenced by traits related to seed quality (weight of 1000 seeds) and yield quality (shelling percent), with a negative influence on PC1. The length of the branch highly influenced the PC3 component, while days to maturity positively contributed to PC4.
Principal components, PC1 and PC2 jointly explained 40.75% of the biplot in Fig. 9. The biplot illustrated negative correlations of the days to maturity and days to 50% flowering with yield attributes, including seed weight, pod weight, number of pods per plant and number of clusters. Positive correlations were observed between seed weight, number of pods per plant, and pod weight. Shelling percent and weight of 1000 seeds were positively correlated, and selecting these traits will be influential in determining seed yield.
Table 4
Eigen values, proportion variability and quantitative traits that accounted for the four principal component of mung bean genotypes
Traits
|
PC1
|
PC2
|
PC3
|
PC4
|
Length of the branch (cm)
|
0.197
|
0.033
|
0.744
|
0.199
|
Number of branches per plant
|
0.654
|
0.079
|
0.040
|
0.045
|
Number of clusters
|
0.515
|
0.273
|
0.408
|
-0.164
|
Number of pods per plant
|
0.747
|
-0.467
|
-0.122
|
0.067
|
Pod length (cm)
|
0.147
|
0.495
|
-0.141
|
0.397
|
Plant height (cm)
|
0.651
|
0.268
|
0.364
|
0.141
|
Pod weight (g)
|
0.862
|
-0.339
|
-0.163
|
0.133
|
Number of seeds per pod
|
0.388
|
0.195
|
-0.128
|
-0.106
|
Seed weight (g)
|
0.901
|
-0.143
|
-0.268
|
-0.011
|
Weight of 1000 seeds (g)
|
0.018
|
0.625
|
-0.267
|
0.368
|
Days to 50% flowering
|
-0.002
|
0.319
|
-0.033
|
0.465
|
Days to maturity
|
-0.215
|
-0.436
|
-0.208
|
0.609
|
Shelling percent
|
0.284
|
0.505
|
-0.407
|
-0.431
|
Eigenvalue
|
3.569
|
1.729
|
1.286
|
1.188
|
Variability (%)
|
27.450
|
13.298
|
9.891
|
9.135
|
Cumulative (%
|
27.450
|
40.748
|
50.639
|
59.774
|
Cluster analysis of selected quantitative traits of mung bean genotypes
In the current study, the dendrogram was clustered using complete linkage, showing the hierarchical clustering of mung bean genotypes. Figure 10 showed numerous clusters portraying associations among genotypes. Cluster analysis categorized genotypes into four major clusters based on their 13 quantitative traits. Cluster III had the highest number of genotypes (42), followed by Cluster IV (28), Cluster II (27) and finally cluster I (14) genotypes.
The mean values of 13 quantitative traits are detailed in Table 5, showcasing differences between clusters for all traits. Genotypes with a higher number of pods per plant, pod weight, number of seeds per pods, seed weight were found in cluster I. While a higher 1000 seed weight was observed in cluster II. Cluster III exhibited maximum mean value for the number of branches per plant, number of clusters and plant height. The highest mean value of the length of the branch was recorded for cluster IV. On the other hand, early flowering and maturity were recorded for cluster I and cluster III, respectively.
Table 5
Estimates of traits means of the mung bean genotypes grouped into clusters using complete linkage method based on quantitative traits
Traits
|
Clusters
|
Grand mean
|
I (14)
|
II (27)
|
III (42)
|
IV (28)
|
Length of the Branch (cm)
|
26.74
|
27.32
|
27.29
|
33.21
|
28.64
|
Number of branches per plant
|
01.82
|
02.05
|
03.00
|
01.94
|
02.20
|
Number of clusters
|
07.50
|
08.35
|
12.35
|
09.80
|
09.50
|
Number of pods per plant
|
37.53
|
20.98
|
35.98
|
26.26
|
30.19
|
Pod length (cm)
|
05.97
|
06.30
|
05.95
|
05.78
|
06.00
|
Plant height (cm)
|
41.98
|
38.22
|
45.75
|
44.06
|
42.50
|
Pod weight (g)
|
24.38
|
12.66
|
22.93
|
16.31
|
19.07
|
Number of seeds per pod
|
10.16
|
08.97
|
09.73
|
09.80
|
09.67
|
Seed weight (g)
|
15.16
|
0.8.04
|
14.07
|
08.56
|
11.46
|
Weight of 1000 seeds (g)
|
41.80
|
53.98
|
41.88
|
43.08
|
45.19
|
Days to 50% flowering
|
37.03
|
38.17
|
37.73
|
38.72
|
37.91
|
Days to maturity
|
66.71
|
65.81
|
64.66
|
65.96
|
65.79
|
Shelling percent
|
64.21
|
67.91
|
63.09
|
53.49
|
62.18
|