3.3 Results
3.3.2 Results of 80 late maturing cowpea genotypes
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3.3.2.2 Performance of cowpea genotypes under drought-stress and non- stress conditions
The yield and yield components of genotypes varied in both stress and non-stress conditions (Table 3.8). The mean yields of genotypes under non-stressed and stressed were 2219 and 1567 kgha-1, respectively. The yield of genotypes ranged between 800 and 4300 kgha-1 and 400 and 3300 kgha-1 under non-stressed and stressed conditions, respectively. Under non-stressed conditions, genotypes N’diambour, FN-3-13-04, IT83D-442, Timbawene moteado, Zimbabwe, INIA-120, Massava-5, IT97K-556-6, Xingove, 24-125B-1, IT96D-610, INIA-72 and Tete-2 were high yielding and produced more than 3000 kgha-1, while genotypes INIA-19C, KVx403, Suvita-2, IT89KD-288, 98K-1382, CC-27, IT98K-317-2, CP-2, Petite-n-green, IT90K-284-2, IT00K-901-6, IT98K-698-2, KVx525 and FN-2-14-04 were low yielding and produced less than 1300 kgha-1 (Table 3.7). Under drought-stressed conditions, genotypes INIA-120, IT96D-610, Tete-2, Massava-14 and Var-3A were high yielding and produced more than 2500 kgha-
1 while genotypes INIA-19C, KVx403, Suvita-2, IT89KD-288, 98K-1382, CC-27, IT98K- 317-2, CP-2, Petite-n-green, IT90K-284-2, IT00K-901-6, IT98K-698-2, KVx525 and FN- 2-14-04 were low yielding and produced less than 1300 kgha-1 (Table 3.8).
Drought stress reduced yield and yield components but genotypes responded differently to drought stress. The yield of genotypes Zimbabwe, Xingove, IT83D-442, N’diambour, Massava-5 and Massava-11 was reduced by more than 50% while that of genotypes INIA-120, IT96D-610, Tete-2, IT95K-201-15, CC-36, Ecute, KVx403 and FN- 2-14-04 was not affected (Table 3.8). The genotypes with severe yield reduction also registered severe reduction in number of pods per plant. In general, severe yield reduction was recorded on high yielding genotypes than in low yielding ones. The number of seeds per pod and hundred seed weight were in general less affected by drought stress.
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Correlation analysis indicated that yield was only significantly correlated with number of pods per plant in both stressed and non-stressed conditions (r=0.83, p<0.01; r=0.74, p<0.01), respectively (Table 3.9 and 3.10).
Table 3.9: Correlations among yield, number of pods per plant, number of seeds per pod and 100-seed weight of 80 late maturing genotypes grown under non-stress conditions
Yield Pods per plant Seeds per pod 100-seed weight
Yield 1.00
Pods per plant 0.8335** 1.00
Seeds per pod 0.1383 0.0024 1.00
100-seed weight 0.1217 -0.0170 -0.0507 1.00
Table 3.10: Correlations among yield, number of pods per plant, number of seeds per pod and 100-seed weight of 80 late maturing genotypes grown under drought-stressed conditions
Yield Pods per plant Seeds per pod 100-seed weight
Yield 1.00
Pods per plant 0.7394** 1.00
Seeds per pod 0.1452 0.0474 1.00
100-seed weight 0.0380 -0.1745 -0.1101 1.00
The stress tolerance indices of a sub-set of 80 late genotypes are indicated in Table 3.11. Genotypes that combined lower tolerance index and stress susceptibility index and higher mean productivity and stress tolerance index were drought tolerant.
Examples of these genotypes are INIA-120, IT96D-610, INIA-72, Tete-2, INIA-17G, INIA-19F and IT95K-207-15. In addition to drought tolerance, genotypes INIA-120, IT96D-610, INIA-72 and Tete-2 were high yielding. In contrast, genotypes that combined higher tolerance index and stress susceptibility index and lower mean productivity or stress tolerance index were susceptible. Examples of these genotypes are IT83D-442, Zimbabwe, Massava-5 and Xingove. Despite their drought susceptibility, IT83D-442, Zimbabwe, Massava-5 and Xingove were high yielding.
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Correlation analysis among drought tolerance indices and stressed and non- stressed yield are presented in Table 3.12. The results indicated that stress tolerance index correlated strongly and positively with non-stressed yield, stressed yield, mean productivity and geometric mean productivity. The correlation between stress tolerance index and geometric mean productivity was one. Stress susceptibility index was correlated with tolerance index and non-stressed yield. The correlations between non-stressed and stressed yield was 0.51.
Table 3.12: Correlation among mean productivity (MP), geometric mean productivity (GMP), tolerance index (TOL), stress susceptibility index (SSI), stress intensity (STI), stressed (Ys) and non-stressed yield (Yp) for 80 genotypes
Ys Yp MP TOL GMP SSI STI
Ys 1.00
Yp 0.51** 1.00
MP 0.82** 0.91** 1.00
TOL -0.24 0.71** 0.36 1.00
GMP 0.90** 0.83** 0.98** 0.20 1.00
SSI -0.47 0.46 0.08 0.90** -0.07 1.00
STI 0.90** 0.83** 0.98** 0.20 1.00** -0.07 1.00
Principal component analysis and biplot displays of 80x7 data matrix are illustrated in Figures 3.2. In the 80x7 data matrix, the PC1 explained 72.32% of the total variation and had high correlation between yield potential, geometric mean productivity, mean productivity and stress tolerance index. This dimension can be named yield potential-mean productivity and separated genotypes with high yield potential-mean productivity from genotypes with low yield potential-mean productivity. Positive correlation was observed between stress tolerance index and geometric mean productivity, stress tolerance index and mean productivity, stress tolerance index and stressed yield and stress tolerance index and yield potential.
The PC2 explained 27.52% of the total variation and had correlation with stressed yield, stress susceptibility index and tolerance index. This dimension can be named stress tolerance dimension and it separated stress tolerant genotypes from stress susceptible genotypes. In relation to the two components of the biplot, the genotypes fell into distinct clusters that corresponded to their yield potential and stress- tolerance. Stress tolerance attributes STI, GMP, MP and Ys were correlated with genotypes INIA72, INIA-120, IT96D-610, Massava-14, Tete-2 and Var3A which
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represent the high yielding and stress tolerant genotypes. Genotypes IT83D-442, Massava-5, N’diambour, Xingove, Zimbabwe were correlated with SSI and TOL.
Genotypes were distributed over the four quadrants of the biplot space according to their yield potential and stress tolerance.
Figure 2: Biplot display of mean productivity (MP), geometric mean productivity (GMP), tolerance index (TOL), stress susceptibility index (SSI), stress intensity (STI) and genotype yields of 80 genotypes grown under moderate stress (SI=0.30) and non-stressed conditions.
P r i n c i p a l C o m p o n e n t B ip l o t
9 9 K 1 2 4
Z im X in g o v e
V a r 3 A
T m t d o T C m e
T e t 2 S V it a 2
P I d 4 P I d 3
P id 2 P I d 1
P e t it
N d m b M I a w e
M n g e
M v a 5
M v a 1 4
M v a 1 1 M p t o K V x 5 2 5
KV x 4 2 1 K V x 4 0 3
K V x 3 9 6
1 2 5 B 5 8 - 5 3
5 8 - 5 7
9 5 - 8 2 5 9 8 k - 1 3 8
9 8 k - 4 1 2 CC 2 7
C C 3 6
C P 2
E c t e
K n d 1 K n d 2 F N - 1 - 1 3 F N - 1 - 1 4
F N - 2 - 1 1
F N - 2 - 1 3 F N - 2 - 1 4
F N - 2 - 9
G lK I A R 7 / 8
I A R 8 / 7
I 1 7 G I 1 9 C
I 1 9 F
I 1 20
I 1 5 2 I 1 7 B
I 3 5
I 4 0
I 4 1
I 7 2 I 7 3
I r C l 0 0 K 9 0 1
8 1 D 1 1 3 7
8 3 D 4 4 2 8 4 D 4 6 0
8 6 D 4 7 2 8 9 K D 2 8
9 0 K2 84
9 3 K 5 0 3
9 5 K 1 0 9 0 9 5 K 1 0 9 5
9 5 K 2 0 7
9 6 D 6 1 0
9 7 K 2 0 7
9 7 K 4 6 1
9 7 K 5 5 6 9 7 K 8 1 9 9 8 K1 1 11
9 8 K - 1 2 8
9 8 K 2 0 5
9 8 K 3 1 7
9 8 K 4 2 8
9 8 K 4 9 8 9 8 K 6 9 8
Y s
Y p
T O L
S T I
S S I
M P G M P
4 - 4
- 4 0
2 2
- 2 - 2
0
P C
2
Ys SSI TOL
PC 1 Yp, MP, GMP, STI 72.32%
Group A
Group B Group D
Group C
27.52%
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