Understanding the nature and extent of association between yield and yield related traits is the prerequisite study for any underutilized crop improvements of sustainable genetic enhancement . However , there is a lack of sufficient information on seed yield and related trait correlation and path coefficient analysis of cowpea in Ethiopia. To fill the existing knowledge gap, the present study was conducted to determine the nature and extent of phenotypic and genotypic correlation and path coefficient analysis among 18 quantitative traits. A total of 324 cowpea landraces were tested in 18 × 18 simple lattice design at Melkassa Agricultural Research Center and Miesso sub center during 2016 cropping season. The magnitude of genotypic correlations was higher than phenotypic correlations in most traits at both locations; this implies that the traits under consideration were genetically controlled. Seed yield was positively and highly significantly correlated with most of the traits at phenotypic and genotypic levels, indicating the presence of strong inherited association between seed yield and the other 17 traits. Almost all traits genotypic direct and indirect effects were higher than the phenotypic direct and indirect effects; this indicated that the other traits had a strong genetically inherited relationship with seed yield. Genotypic path coefficient analysis revealed that days to flowering, biomass and harvest index at Miesso, and seed thickness, plant height, days to maturity and biomass at Melkassa had relatively high positive direct effect on seed yield. However, seed width and hundred seed weight had exerted negative direct effect on seed yield at each location. Phenotypic path coefficient analysis showed that biomass and harvest index had exerted high positive direct effect on seed yield at both locations. From these results it can be concluded from this study that seed yield in cowpea can be improved by focusing on traits pod length, seed length, seed thickness, seed width, biomass and harvest index at both locations. The information obtained from this study can be used for genetic enhancement of cowpea thereby develop ing high yielding varieties.
Cowpea (Vigna unguiculata L.) is the most economically important indigenous African grain legume producing a source of economic livelihood and nutritional well-being for rural poor and urban consumers [
Cowpea plays a critical role in the lives of millions of people in Africa and other parts of the developing world, where it is a major source of dietary protein that nutritionally complements staple low-protein cereal and tuber crops, and is a valuable and dependable commodity that produces income for poor farmers [
Cowpea is primarily grown in drier regions of the world where it is one of the most drought tolerant food legumes [
Therefore, understanding the nature and intensity of association between two or more quantitative traits between yield and yield contributing traits, correlation simply measures that mutual relationship between yield and yield contributing traits. Thus, correlation helps in the selection of superior genotype from diverse genetic populations [
In Ethiopia, cowpea is grown in southern and eastern Tigray zone, north and south Wollo zone, east and west Haraghe zone, Ethio-Somali region, Afar region, Wolayita zone and Jinka zone. Dray cowpea seed used for human consumption is the most important product of the cowpea plant; these grains can either be boiled or “nifiro” or converted into other food products like “Shiro” and “Kollo”. In Gambella region used for nutritious vegetable soup; the young seedling, leaves, green pod and peas are used for salad in vegetarian diets as well as different dishes in the area. In addition to human consumption cowpea haulms and chaff are used as livestock feeds in all producing regions and are also beneficial in maintaining soil fertility thus making it an important component of any cropping system. Those regions adversely affected by erratic rainfall patterns [
However, lack of sufficient information on seed yield and related trait correlation and path coefficient analysis of cowpea in Ethiopia. Therefore, the objectives of present study were to determine the nature and extent of phenotypic and genotypic correlations among 18 quantitative traits of 324 cowpea landraces and to identify the most important traits for indirect selection in future cowpea breeding programs.
The field experiment was conducted from July to November 2016 at Melkassa Agricultural Research Center (MARC) and Miesso during the main cropping season. MARC is located at 39˚12'N and 8˚24'E and 1550 meters above sea level (masl) and received five months mean rainfall of 140.96 mm (total 704.8 mm). The minimum and maximum temperatures were 14.35˚C and 28.22˚C, respectively. The soil texture of the field site was Andosoil with the pH 7.6. The second testing site (Miesso) is located at 9˚14'N (Latitude) and 40˚45'E (Longitude) and 1470 meters above sea level (masl) received five months mean rainfall of 84 mm (total 420 mm). The minimum and maximum temperatures were 15.2˚C and 31.1˚C, respectively. The soil texture of the field site was Vertisols.
A total of 324 cowpea landraces collected from different agro ecological regions of Ethiopia. 72, 55, 52, 50, 14, and 68 landraces were collected from Oromia, Amhara, Gambella, SNNP, Tigray regions, and Unknown (the landraces had no passport data), respectively. Of these, 311 landraces were obtained from Melkassa Agricultural Research Center (MARC), Ethiopia. Five landraces of Ethiopian origin were obtained from International Institute of Tropical Agriculture (IITA), while the rest eight are improved (released) varieties.
The experiments were laid out using 18 × 18 simple lattice design. The plot size was 2 m long, 0.75 m between rows and 0.2 m between plants. It consists two rows accommodating 10 plants per row. The distance between plots, intra blocks and replications was 1 m, 1.5 m and 2 m, respectively. The data were collected from the two rows.
The quantitative data were collected according to the descriptor of cowpea (Vigna unguiculata) developed by the International Board for Plant Genetic Resources [
The data were subjected to analysis of variance to check the presence of variation among the genotypes for the tested traits and then based on the ANOVA result; all highly significant traits were promoted for correlation and path coefficient analyses. Phenotypic and genotypic correlations between yield and yield related traits were estimated using the method described by [
The phenotypic correlation coefficient ( r p x y ) = C o v p x y ( σ 2 p x ) ( σ 2 p y )
The genotypic correlation coefficient ( r g x y ) = C o v g x y ( σ 2 g x ) ( σ 2 g y )
where, rpxy is phenotypic correlation coefficient and Genotypic correlation coefficient ( r g x y ) between character x and y; Covpxy and Covgxy are phenotypic covariance and genotypic covariance between character x and y; σ g x 2 and σ g y 2 are genotypic variances traits x and y; σ p x 2 and σ p y 2 are phenotypic variances of traits x and y, respectively. The coefficient of correlation was tested using tabulated value at n − 2 degree of freedom, at 5% and 1% probability level, where n is the number of treatments (landraces) as described by [
Microsoft Excel computer program was employed for phenotypic and genotypic path coefficient analysis as well as estimation of residual effect. Path coefficient analysis was conducted as suggested by [
R i j = P i j + ∑ r i k P k
where, rij is mutual association between the independent character (i) and dependent traits (i) as measured by correlation coefficients, pij is components of direct effects of the independent traits (i) on the dependent traits (j), ∑ r i k P k = summation of components of indirect effect of a given independent character (i) on the dependent traits (j) via all other independent traits (k).
The residual effect (R) was estimated using the formula shown below [
R = √1 − R2 Where, R 2 = ∑ r i j p i j .
Estimates of phenotypic and genotypic correlation coefficients between each pair of traits are presented in
Seed yield is a complex trait and that is set by the interactive effects of several yield associated traits that area unit successively influenced by their genetic structures and also the environmental factors. Thus, the direct measurement and improvement of seed yield itself are also may be ambiguous due to the influence of the environmental factors and the nature of genetic makeup of the yield trait. Therefore, it is essential to investigate information the relative contribution of various components to yield performance. The simple genotypic and phenotypic correlation is a vital tool for this goal because the understanding of correlation is key one choice is to be created on many traits at a time through some contemporary selections of cowpea. In this study, the results of seed yield showed
Traits | DF | GFP | DM | PH | PdL | NRPP | NPPPd | TLW | PL | PdW | nsPP | SL | SW | ST | HSW | Yld | BM | HI |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | −0.31** | 0.87** | 0.20** | 0.01 ns | −0.04 ns | −0.05 ns | 0.12* | 0.30** | 0.38** | 0.37** | 0.24** | 0.20** | 0.16** | 0.20** | −0.17** | 0.02 ns | −0.34** | |
GFP | −0.37** | 0.18** | 0.14* | 0.07 ns | −0.09 ns | −0.14* | 0.25** | −0.31** | −0.48** | −0.33** | −0.14* | −0.16** | −0.15* | −0.27** | −0.47** | −0.46** | −0.34** | |
DM | 0.65** | 0.46** | 0.26** | 0.02 ns | −0.11* | −0.11 ns | 0.21** | 0.14* | 0.13* | 0.19** | 0.17** | 0.13** | 0.09 ns | 0.06 ns | −0.41** | −0.23** | −0.54** | |
PH | 0.15* | 0.00 ns | 0.14 ns | −0.14** | 0.06* | 0.08 ns | 0.17** | 0.14* | 0.13** | 0.24** | 0.09** | 0.05* | 0.08 ns | 0.04 ns | 0.00** | 0.22** | −0.22** | |
NPPP | −0.14* | −0.04 ns | −0.17** | −0.18** | 0.60** | 0.55** | −0.20** | 0.09 ns | −0.04 ns | 0.03 ns | 0.03 ns | 0.02 ns | 0.05 ns | 0.00 ns | 0.25** | 0.14* | 0.31** | |
PdL | −0.01 ns | −0.07 ns | −0.08 ns | 0.06 ns | 0.56** | 0.40** | 0.18** | 0.21** | 0.18** | 0.12** | 0.17** | 0.16** | 0.16** | 0.14** | 0.31** | 0.51** | 0.20** | |
NPPPd | −0.04 ns | −0.02 ns | −0.05 ns | 0.00 ns | 0.18** | 0.11* | −0.12* | 0.23** | 0.31** | 0.18 ns | 0.11** | 0.21* | 0.26** | 0.18 ns | 0.29** | 0.37** | −0.05** | |
TLW | −0.02 ns | 0.05 ns | 0.02 ns | 0.00 ns | −0.02 ns | 0.02 ns | 0.00 ns | 0.15* | 0.15* | −0.22** | 0.52** | 0.25** | 0.27** | 0.36** | 0.22** | 0.16** | 0.48** | |
PL | 0.22** | −0.08 ns | 0.13 ns | 0.09 ns | 0.12 ns | 0.11 ns | 0.11 ns | 0.08 ns | 0.83** | 0.80** | 0.72** | 0.83** | 0.82** | 0.74** | 0.23** | 0.36** | 0.09* | |
PdW | 0.26** | −0.14** | 0.13 ns | 0.06 ns | 0.09 ns | 0.04 ns | 0.09 ns | 0.04 ns | 0.72** | 0.75* | 0.73** | 0.85* | 0.81** | 0.83* | 0.28** | 0.38** | 0.16** | |
nsPP | 0.27** | −0.12** | 0.16** | 0.15** | 0.03 ns | 0.06 ns | 0.10 ns | −0.07 ns | 0.75** | 0.61 ns | 0.37** | 0.54** | 0.54* | 0.42 ns | 0.14** | 0.31** | −0.02** | |
SL | 0.17** | −0.08 | 0.10 ns | 0.06 ns | 0.11 ns | 0.08 ns | 0.05 ns | 0.19** | 0.62** | 0.60 ns | 0.31** | 0.89** | 0.88** | 0.92** | 0.34** | 0.50** | 0.22** | |
SW | 0.18** | −0.08 ns | 0.10 ns | 0.05 ns | 0.09 ns | 0.05 ns | 0.11 ns | 0.11* | 0.69** | 0.70 ns | 0.43** | 0.84** | 1.00** | 0.89** | 0.40** | 0.51** | 0.26** | |
ST | 0.15* | −0.09 ns | 0.07 ns | 0.05 ns | 0.10 ns | 0.06 ns | 0.12 ns | 0.11* | 0.69** | 0.66 ns | 0.42** | 0.84*** | 0.97** | 0.89** | 0.40** | 0.53** | 0.30** | |
HSW | 0.16** | −0.11 ns | 0.06 ns | 0.04 ns | 0.09 ns | 0.03 ns | 0.09 ns | 0.14 ns | 0.62** | 0.69 ns | 0.35** | 0.81** | 0.79** | 0.77** | 0.32** | 0.43** | 0.25** | |
Yld | −0.13* | −0.19** | −0.28** | 0.02 ns | 0.18** | 0.16** | 0.15* | 0.07 ns | 0.21** | 0.21 ns | 0.14** | 0.26** | 0.32** | 0.32** | 0.25** | 1.00** | 0.91** | |
BM | 0.00 ns | −0.21 ns | −0.16** | 0.10 ns | 0.19** | 0.12* | 0.15* | 0.05 ns | 0.23** | 0.23 ns | 0.18** | 0.28** | 0.35** | 0.35** | 0.26** | 0.76** | 0.84** | |
HI | −0.18 | −0.08 ns | −0.24** | −0.09 ns | 0.13* | 0.13* | 0.05* | 0.09 ns | 0.10** | 0.12* | 0.00 ns | 0.15* | 0.19** | 0.21** | 0.16** | 0.72** | 0.26** |
DM = days to flowering, DM days to maturity, GFP = grain filling period, PH = plant height, NPBPP = number of primary branches per plant, NPPP = number of pods per plant, NSPP = number of seeds per pod, PC = pod clearance, PL = pod length, PdW = pod width, PdL = peduncle length, NPPPd = number of pods per peduncle, TLL = terminal leaflet length, TLW = terminal leaflet width and NRPP = number of racemes per plant, HSW = hundred seed weight, SL = seed length, ST = seed length, SW = seed width, Yld = seed yield per plot, BM = biomass and HI = harvest index.
significant and positive genotypic and phenotypic correlations with biomass and harvest index at both environments (
On the other hand, seed yield showed negative and highly significant genotypic and phenotypic correlation with days to flowering, days to maturity and grain filling period at Miesso (
Traits | DF | GFP | DM | PH | PdL | NRPP | NPPPd | TLW | PL | PdW | NSPP | SL | SW | ST | HSW | Yld | BM | HI |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | 0.20** | 0.96** | 0.45** | 0.09 ns | 0.12* | −0.67** | 0.19** | 0.73** | 0.57** | 0.34** | 0.54** | 0.58** | 0.53** | 0.86** | 0.30** | 0.35** | 0.20** | |
GFP | −0.02 ns | 0.46** | 0.09 ns | 0.48** | −1.00** | 0.24** | 0.47** | −0.19** | −0.71** | −0.28** | −0.14* | −0.43** | −0.35 | 0.28** | −0.06 ns | 0.10 ns | −0.21** | |
DM | 0.80** | 0.58 ns | 0.47** | 0.20** | −0.15** | −0.59** | 0.29** | 0.61** | 0.38** | 0.24** | 0.47** | 0.43** | 0.41** | 0.83** | 0.26** | 0.38** | 0.13* | |
PH | 0.18** | 0.06 ns | 0.19** | 0.14* | −0.13* | −0.71** | 0.09 ns | 0.04 ns | 0.18** | 0.20** | 0.17** | 0.05* | 0.06** | 0.35** | 0.13* | 0.12** | 0.19** | |
PdL | 0.06 ns | 0.09 ns | 0.11 ns | 0.15** | 0.25** | 0.27** | −0.43** | −0.10 ns | 0.28** | 0.25** | 0.24** | 0.18*** | 0.11* | −0.26** | 0.14* | 0.24** | 0.11 ns | |
NRPP | 0.00 ns | −0.11 ns | −0.07 ns | 0.06 ns | 0.08 ns | −0.11** | −0.25** | 0.33** | 0.58 | 0.34** | 0.29** | 0.33** | 0.49** | 0.25** | 0.17** | 0.16** | 0.11** | |
NPPPd | −0.25** | 0.07 ns | −0.16** | −0.06 ns | 0.11 ns | 0.06 ns | −1.00** | −1.00** | −0.86** | −1.00** | −0.51** | −0.64** | −0.51** | −1.00** | −0.25** | −0.25** | −0.29** | |
TLW | 0.04 ns | 0.05 ns | 0.07 ns | 0.18** | 0.02 ns | 0.13** | −0.10 ns | 0.05 ns | 0.62** | −0.02 ns | 0.41** | 0.38** | 0.45** | 1.00** | 0.38** | 0.49** | 0.30** | |
PL | 0.38** | −0.04 ns | 0.28** | 0.06 ns | 0.11 ns | 0.16** | −0.18 | 0.12* | 0.85** | 0.65** | 0.94** | 0.99** | 1.00** | 0.50** | 0.47** | 0.56** | 0.31** | |
PdW | 0.31** | −0.02 ns | 0.23** | 0.05 ns | 0.10 ns | 0.16** | −0.19 | 0.17** | 0.46** | 0.52** | 0.74** | 0.83** | 0.81** | 0.74** | 0.62** | 0.60** | 0.68** | |
NSPP | 0.18** | −0.03 ns | 0.13* | 0.02 ns | 0.09 ns | 0.07 ns | −0.16** | −0.10 ns | 0.29** | 0.27** | 0.22** | 0.32** | 0.21** | 0.04 ns | 0.30** | 0.26** | 0.39** | |
SL | 0.36** | −0.002 ns | 0.29** | 0.07 ns | 0.11* | 0.14* | −0.17** | 0.20** | 0.53** | 0.45** | 0.11 ns | 0.83** | 0.86** | 1.00** | 0.48** | 0.47** | 0.45** | |
SW | 0.40** | −0.04 ns | 0.30** | 0.01 ns | 0.09 ns | 0.21** | −0.19** | 0.17** | 0.55** | 0.47** | 0.19 | 0.77** | 0.99** | 1.00** | 0.50** | 0.44** | 0.50** | |
ST | 0.37** | −0.02 ns | 0.29** | 0.00 ns | 0.05 ns | 0.22** | −0.16** | 0.17** | 0.54** | 0.45** | 0.13* | 0.78** | 0.91** | 1.00** | 0.48** | 0.47** | 0.44** | |
HSW | 0.19** | 0.03 ns | 0.17** | 0.07 ns | 0.01 ns | 0.04 ns | −0.11* | 0.13* | 0.20** | 0.19** | 0.03 ns | 0.37** | 0.40** | 0.40** | 0.29** | 0.10** | 0.38** | |
Yld | 0.17** | −0.01 ns | 0.13* | 0.07 ns | 0.15* | 0.16** | −0.02 ns | 0.14* | 0.35** | 0.31** | 0.19** | 0.39** | 0.41** | 0.38** | 0.07** | 0.95** | 0.99** | |
BM | 0.21** | −0.01 ns | 0.16** | 0.02 ns | 0.09 ns | 0.11** | −0.04 ns | 0.09 ns | 0.29** | 0.24** | 0.14* | 0.32** | 0.33** | 0.33** | 0.03** | 0.78** | 0.89** | |
HI | 0.09 ns | −0.01 ns | 0.06 ns | 0.10 ns | 0.16** | 0.14* | −0.02 ns | 0.13* | 0.26** | 0.28** | 0.18** | 0.32** | 0.35** | 0.30** | 0.08** | 0.82** | 0.31** |
DM = days to flowering, DM days to maturity, GFP = grain filling period, PH = plant height, NPBPP = number of primary branches per plant, NPPP = number of pods per plant, NSPP = number of seeds per pod, PC = pod clearance, PL = pod length, PdW = pod width, PdL = peduncle length, NPPPd = number of pods per peduncle, TLL = terminal leaflet length, TLW = terminal leaflet width and NRPP = number of racemes per plant , HSW = hundred seed weight, SL = seed length, ST = seed length, SW = seed width, Yld = seed yield per plot, BM = biomass and HI = harvest index.
highly significant genotypic association between seed yield with hundred seed weight, seed per pod, pod length and number of pod per plant. [
Seed yield per plot showed intermediate positive and highly significant correlation with seed length, seed length, seed width, number of seeds per pod and number of pods per plant at genotypic and phenotypic levels (
Generally, at both locations, almost all traits found to have highly significant and positive correlation with seed yield per plot at genotypic and phenotypic levels. It implies that there is an enormous chance of exploiting the potential of these traits for effective selection in cowpea improvement programme.
At Miesso, days to maturity was significantly and positively correlated with days to flowering, grain filling period at genotypic and phenotypic levels. This result in agreement with [
In the present study, all the traits, except days to maturity and grain filling period showed positive phenotypic and genotypic correlations with biomass. Some of these had significant positive correlations. It is in harmony with [
At Melkassa, all traits, except number of pods per peduncle and peduncle length showed positive and highly significant correlation with days to flowering at genotypic level. The traits like days to maturity, plant height, pod length, peduncle length, number of seeds per pod, seed length, seed thickness, seed width and hundred seed weight were also showed positive and highly significant correlation with days to flowering at the phenotypic level. This result in line with [
All traits, except the number of seeds per pod, number of racemes per plant and peduncle length significantly high and positive correlated with the number of pods per peduncle at genotypic and phenotypic levels. Highly significant and positive correlations were recorded between a number of pods per peduncle and number of seeds per pod, pod width, seed length, seed thickness, seed width, hundred seed weight, biomass and harvest index at genotypic and phenotypic levels. This result in line with, [
Hundred seed weight showed perfect and highly significant correlation with terminal leaflet width (rg = 1.00), number of pods per peduncle (rg = −1.00), seed length (rph = 1.00), seed thickness (rph = 1.00) and seed width (rph = 1.00). In addition, the trait like grain filling period, plant height, peduncle length and number of racemes per plant showed positive and highly significant correlation with hundred seed weight at the phenotypic level (
Path coefficient analysis has been used to evaluate selection criteria in several crops. This technique is useful in determining the direct influence of one variable on another and also separates the correlation coefficient into its components of direct and indirect effects [
The results of genotypic path coefficient analysis of seed yield with other 18 traits Miesso and Melkassa are presented in
Traits | DF | GFP | DM | PH | PC | NPPP | PdL | NRPP | NPPPd | TLW | PL | PdW | NSPP | SL | SW | ST | 100S | BM | HI |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | −0.635 | 0.198 | −0.552 | −0.127 | −0.188 | 0.119 | −0.006 | 0.027 | 0.031 | −0.077 | −0.193 | −0.240 | −0.237 | −0.151 | −0.125 | −0.101 | −0.127 | −0.013 | 0.218 |
GFP | 0.198 | −0.813 | −0.147 | −0.116 | 0.071 | 0.024 | −0.057 | 0.071 | 0.112 | −0.206 | 0.252 | 0.391 | 0.270 | 0.117 | 0.131 | 0.122 | 0.216 | 0.374 | 0.273 |
DM | −0.706 | −0.147 | 0.499 | 0.015 | −0.013 | 0.003 | 0.000 | 0.002 | 0.004 | 0.016 | −0.049 | −0.094 | −0.064 | −0.018 | −0.016 | −0.012 | −0.028 | −0.005 | 0.059 |
PH | 0.100 | 0.071 | 0.128 | 0.565 | 0.412 | −0.195 | −0.078 | 0.035 | 0.043 | 0.094 | 0.082 | 0.071 | 0.134 | 0.051 | 0.027 | 0.043 | 0.020 | 0.124 | −0.125 |
PC | 0.168 | −0.049 | 0.132 | 0.412 | −0.451 | 0.001 | −0.152 | −0.088 | −0.089 | 0.024 | −0.081 | −0.041 | −0.070 | −0.072 | −0.044 | −0.057 | −0.045 | −0.111 | −0.048 |
NPPP | 0.085 | 0.013 | 0.098 | 0.156 | 0.001 | 0.360 | 0.121 | 0.070 | 0.071 | −0.019 | 0.065 | 0.032 | 0.056 | 0.058 | 0.035 | 0.045 | 0.036 | 0.088 | 0.038 |
PdL | 0.003 | 0.025 | 0.008 | −0.050 | 0.121 | 0.202 | 0.373 | 0.197 | 0.150 | 0.067 | 0.077 | 0.066 | 0.043 | 0.062 | 0.058 | 0.059 | 0.053 | 0.188 | 0.075 |
NRPP | −0.016 | −0.033 | −0.042 | 0.023 | 0.073 | 0.224 | 0.197 | −0.255 | 0.024 | 0.017 | 0.017 | 0.008 | 0.014 | 0.013 | 0.010 | 0.012 | 0.005 | 0.019 | 0.014 |
NPPPd | 0.013 | 0.035 | 0.027 | −0.019 | −0.050 | −0.141 | −0.103 | −0.094 | −0.310 | 0.036 | −0.073 | −0.095 | −0.055 | −0.034 | −0.064 | −0.081 | −0.057 | −0.115 | 0.016 |
TLW | −0.037 | −0.079 | −0.064 | −0.051 | 0.016 | 0.061 | −0.055 | −0.081 | 0.036 | 0.039 | 0.006 | 0.006 | −0.009 | 0.021 | 0.010 | 0.011 | 0.014 | 0.006 | 0.019 |
PL | 0.012 | −0.012 | 0.005 | 0.006 | 0.007 | 0.004 | 0.008 | 0.010 | 0.009 | 0.006 | −0.167 | −0.138 | −0.133 | −0.120 | −0.138 | −0.137 | −0.123 | −0.060 | −0.015 |
PdW | −0.063 | 0.080 | −0.022 | −0.021 | −0.015 | 0.006 | −0.029 | −0.020 | −0.051 | −0.024 | −0.138 | 0.286 | 0.215 | 0.210 | 0.245 | 0.231 | 0.236 | 0.110 | 0.047 |
NSPP | 0.107 | −0.095 | 0.054 | 0.068 | 0.045 | 0.009 | 0.033 | 0.062 | 0.051 | −0.063 | 0.229 | 0.215 | −0.309 | −0.114 | −0.168 | −0.166 | −0.131 | −0.094 | 0.007 |
SL | −0.073 | 0.044 | −0.051 | −0.028 | −0.049 | −0.009 | −0.051 | −0.060 | −0.034 | −0.162 | −0.222 | −0.226 | −0.114 | 0.152 | 0.135 | 0.134 | 0.140 | 0.076 | 0.033 |
SW | 0.030 | −0.025 | 0.020 | 0.007 | 0.015 | 0.003 | 0.024 | 0.023 | 0.031 | 0.038 | 0.126 | 0.130 | 0.083 | 0.135 | −1.550 | −1.544 | −1.384 | −0.793 | −0.400 |
ST | −0.246 | 0.233 | −0.140 | −0.117 | −0.195 | −0.084 | −0.247 | −0.281 | −0.408 | −0.426 | −1.274 | −1.250 | −0.832 | −1.366 | −1.544 | 2.240 | 1.993 | 1.180 | 0.669 |
HSW | 0.449 | −0.596 | 0.134 | 0.079 | 0.222 | −0.010 | 0.317 | 0.174 | 0.413 | 0.815 | 1.650 | 1.849 | 0.951 | 2.069 | 2.000 | 1.993 | −0.730 | −0.317 | −0.185 |
BM | −0.015 | 0.335 | 0.166 | −0.161 | −0.179 | −0.106 | −0.369 | −0.212 | −0.270 | −0.120 | −0.262 | −0.280 | −0.223 | −0.365 | −0.374 | −0.385 | −0.317 | 0.446 | 0.375 |
HI | −0.153 | −0.150 | −0.242 | −0.099 | 0.047 | 0.139 | 0.090 | 0.094 | −0.024 | 0.213 | 0.040 | 0.073 | −0.010 | 0.098 | 0.115 | 0.133 | 0.113 | 0.375 | 0.158 |
Rg | 0.30** | −0.06 ns | 0.26** | 0.13* |
Residual = 0.147. DM = days to flowering, DM days to maturity, GFP = grain filling period, PH = plant height, NPBPP = number of primary branches per plant, NPPP = number of pods per plant, NSPP = number of seeds per pod, PC = pod clearance, PL = pod length, PdW = pod width, PdL = peduncle length, NPPPd = number of pods per peduncle, TLL = terminal leaflet length, TLW = terminal leaflet width and NRPP = number of racemes per plant, HSW = hundred seed weight, SL = seed length, ST = seed length, SW = seed width, Yld = seed yield per plot, BM = biomass and HI = harvest index.
Traits | DF | GFP | DM | PH | PdL | NRPP | NPPPd | TLW | PL | PdW | NSPP | SL | SW | ST | HSW | BM | HI | rg |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | 1.852 | 0.379 | 1.770 | 0.839 | 0.161 | 0.214 | −1.234 | 0.356 | 1.354 | 1.053 | 0.636 | 1.007 | 1.079 | 0.977 | 1.588 | 0.649 | 0.377 | −0.17** |
GFP | 0.092 | 0.450 | 0.208 | 0.041 | 0.215 | −0.450 | 0.106 | 0.212 | −0.085 | −0.317 | −0.124 | −0.063 | −0.194 | −0.159 | 0.126 | 0.044 | −0.095 | −0.47** |
DM | −1.947 | −0.940 | −2.037 | −0.951 | −0.411 | 0.313 | 1.196 | −0.600 | −1.251 | −0.774 | −0.496 | −0.964 | −0.868 | −0.828 | −1.683 | −0.782 | −0.270 | −0.41** |
PH | 0.037 | 0.007 | 0.038 | 0.081 | −0.290 | 0.272 | 1.454 | −0.176 | −0.078 | −0.359 | −0.406 | −0.344 | −0.094 | −0.123 | −0.705 | −0.235 | −0.391 | 0.00** |
PdL | 0.000 | 0.002 | 0.001 | 0.001 | 0.005 | 0.001 | 0.001 | −0.002 | 0.000 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | −0.001 | 0.001 | 0.000 | 0.25** |
NRPP | −0.004 | 0.035 | 0.005 | 0.005 | −0.009 | −0.035 | 0.004 | 0.008 | −0.011 | −0.020 | −0.012 | −0.010 | −0.012 | −0.017 | −0.009 | −0.006 | −0.004 | 0.31** |
NPPPd | −0.029 | 0.010 | −0.026 | −0.031 | 0.012 | −0.005 | 0.044 | −0.044 | −0.044 | −0.038 | −0.044 | −0.022 | −0.028 | −0.022 | −0.044 | −0.011 | −0.013 | 0.29** |
TLW | 0.011 | 0.028 | 0.017 | 0.005 | −0.025 | −0.015 | −0.059 | 0.059 | 0.003 | 0.037 | −0.001 | 0.024 | 0.022 | 0.027 | 0.059 | 0.029 | 0.018 | 0.22** |
PL | 0.047 | −0.012 | 0.039 | 0.002 | −0.007 | 0.021 | −0.064 | 0.003 | 0.064 | 0.054 | 0.041 | 0.060 | 0.064 | 0.064 | 0.032 | 0.036 | 0.020 | 0.23** |
PdW | −0.024 | 0.030 | −0.016 | −0.008 | −0.012 | −0.025 | 0.037 | −0.027 | −0.036 | −0.043 | −0.022 | −0.032 | −0.036 | −0.035 | −0.031 | −0.026 | −0.029 | 0.28** |
NSPP | −0.007 | 0.006 | −0.005 | −0.004 | −0.005 | −0.007 | 0.020 | 0.000 | −0.013 | −0.011 | −0.001 | −0.002 | −0.002 | −0.002 | −0.001 | −0.001 | −0.001 | 0.14** |
SL | 0.009 | −0.002 | 0.008 | 0.003 | 0.004 | 0.005 | −0.008 | 0.007 | 0.016 | 0.012 | 0.004 | 0.017 | 0.014 | 0.014 | 0.017 | 0.008 | 0.007 | 0.34** |
SW | −0.047 | 0.035 | −0.035 | −0.004 | −0.015 | −0.027 | 0.052 | −0.031 | −0.081 | −0.068 | −0.026 | −0.07 | −0.082 | −0.080 | −0.082 | −0.036 | −0.040 | 0.40** |
ST | 0.055 | −0.037 | 0.043 | 0.006 | 0.012 | 0.051 | −0.053 | 0.047 | 0.105 | 0.085 | 0.023 | 0.090 | 0.1034 | 0.105 | 0.105 | 0.049 | 0.046 | 0.40** |
HSW | −0.041 | −0.013 | −0.039 | −0.016 | 0.012 | −0.012 | 0.047 | −0.047 | −0.024 | −0.035 | −0.002 | −0.05 | −0.047 | −0.047 | −0.047 | −0.005 | −0.018 | 0.32** |
BM | 0.206 | 0.058 | 0.226 | 0.068 | 0.144 | 0.096 | −0.145 | 0.291 | 0.331 | 0.354 | 0.150 | 0.274 | 0.261 | 0.274 | 0.058 | 0.588 | 0.523 | 0.43** |
HI | 0.094 | −0.097 | 0.061 | 0.088 | 0.050 | 0.049 | −0.132 | 0.138 | 0.145 | 0.313 | 0.181 | 0.207 | 0.228 | 0.202 | 0.177 | 0.408 | 0.459 | 0.25** |
Residual = 0.212. DM = days to flowering, DM days to maturity, GFP = grain filling period, PH = plant height, NPBPP = number of primary branches per plant, NPPP = number of pods per plant, NSPP = number of seeds per pod, PL = pod length, PdW = pod width, PdL = peduncle length, NPPPd = number of pods per peduncle, TLL = terminal leaflet length, TLW = terminal leaflet width and NRPP = number of racemes per plant, HSW = hundred seed weight, SL = seed length, ST = seed length, SW = seed width, Yld = seed yield per plot, BM = biomass and HI = harvest index.
On the contrary, [
At Melkassa, the residual effect (0.212) indicated that traits which are included in the genotypic path analysis explained 78.8% of the total variation on seed yield. Days to flowering followed by biomass and harvest index exerted a positive direct effect on seed yield. [
Traits | DF | GFP | DM | PH | PC | NPPP | PdL | NRPP | NPPpd | TLW | PL | PdW | NSPP | SL | SW | ST | HSW | BM | HI |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | −0.027 | 0.010 | −0.018 | −0.004 | −0.004 | 0.004 | 0.000 | 0.003 | 0.001 | 0.001 | −0.006 | −0.007 | −0.007 | −0.005 | −0.005 | −0.004 | −0.004 | 0.000 | 0.005 |
GFP | 0.006 | −0.017 | −0.008 | 0.000 | 0.001 | 0.001 | 0.001 | 0.000 | 0.000 | −0.001 | 0.001 | 0.002 | 0.002 | 0.001 | 0.001 | 0.002 | 0.002 | 0.003 | 0.001 |
DM | −0.019 | −0.014 | −0.030 | −0.004 | −0.003 | 0.005 | 0.002 | 0.003 | 0.001 | −0.001 | −0.004 | −0.004 | −0.005 | −0.003 | −0.003 | −0.002 | −0.002 | 0.005 | 0.007 |
PH | 0.007 | 0.000 | 0.007 | 0.045 | 0.033 | −0.008 | 0.003 | 0.002 | 0.000 | 0.000 | 0.004 | 0.003 | 0.007 | 0.003 | 0.002 | 0.002 | 0.002 | 0.004 | −0.004 |
PC | −0.006 | 0.002 | −0.004 | −0.028 | −0.039 | −0.005 | −0.010 | −0.006 | −0.003 | 0.000 | −0.005 | −0.002 | −0.004 | −0.003 | −0.003 | −0.003 | −0.002 | −0.006 | −0.002 |
NPPP | −0.003 | −0.001 | −0.004 | −0.004 | 0.003 | 0.024 | 0.011 | 0.014 | 0.005 | −0.001 | 0.001 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | −0.001 | 0.001 | 0.005 |
PdL | 0.000 | 0.002 | 0.002 | −0.001 | −0.006 | −0.011 | −0.024 | −0.011 | −0.004 | 0.001 | −0.003 | −0.002 | −0.001 | −0.003 | −0.002 | −0.002 | −0.002 | −0.004 | −0.003 |
NRPP | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
NPPpd | −0.001 | −0.001 | −0.002 | 0.000 | 0.003 | 0.007 | 0.006 | 0.004 | 0.037 | 0.000 | 0.004 | 0.003 | 0.004 | 0.002 | 0.004 | 0.004 | 0.003 | 0.005 | 0.002 |
TLW | 0.000 | −0.001 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | −0.012 | −0.001 | 0.000 | 0.001 | −0.002 | −0.001 | −0.001 | −0.002 | −0.001 | −0.001 |
PL | 0.004 | −0.001 | 0.002 | 0.001 | 0.002 | 0.001 | 0.002 | 0.002 | 0.002 | 0.001 | 0.017 | 0.012 | 0.013 | 0.011 | 0.012 | 0.012 | 0.011 | 0.004 | 0.002 |
PdW | −0.002 | 0.001 | −0.001 | −0.001 | −0.001 | 0.000 | −0.001 | 0.000 | −0.001 | 0.000 | −0.006 | −0.009 | −0.005 | −0.005 | −0.006 | −0.006 | −0.006 | −0.002 | −0.001 |
NSPP | 0.011 | −0.005 | 0.007 | 0.006 | 0.005 | 0.000 | 0.001 | 0.003 | 0.004 | −0.003 | 0.031 | 0.025 | 0.041 | 0.013 | 0.018 | 0.017 | 0.014 | 0.007 | 0.000 |
SL | 0.010 | −0.005 | 0.006 | 0.004 | 0.005 | 0.000 | 0.006 | 0.005 | 0.003 | 0.011 | 0.037 | 0.036 | 0.019 | 0.060 | 0.051 | 0.050 | 0.049 | 0.017 | 0.009 |
SW | 0.020 | −0.010 | 0.011 | 0.005 | 0.008 | −0.001 | 0.010 | 0.005 | 0.012 | 0.013 | 0.078 | 0.079 | 0.048 | 0.096 | 0.113 | 0.109 | 0.089 | 0.039 | 0.022 |
ST | −0.027 | 0.017 | −0.012 | −0.010 | −0.012 | −0.001 | −0.019 | −0.011 | −0.023 | −0.020 | −0.126 | −0.122 | −0.077 | −0.154 | −0.178 | −0.184 | −0.142 | −0.064 | −0.038 |
HSW | −0.001 | 0.001 | 0.000 | 0.000 | 0.000 | 0.000 | −0.001 | 0.000 | −0.001 | −0.001 | −0.004 | −0.005 | −0.002 | −0.006 | −0.006 | −0.005 | −0.007 | −0.002 | −0.001 |
BM | 0.002 | −0.126 | −0.100 | 0.059 | 0.090 | 0.038 | 0.116 | 0.073 | 0.089 | 0.033 | 0.140 | 0.139 | 0.110 | 0.174 | 0.212 | 0.211 | 0.157 | 0.611 | 0.159 |
HI | −0.101 | −0.047 | −0.133 | −0.050 | 0.31 | 0.113 | 0.073 | 0.073 | 0.027 | 0.052 | 0.054 | 0.66 | −0.001 | 0.082 | 0.109 | 0.116 | 0.090 | 0.259 | 0.561 |
Residual = 0.337. DM = days to flowering, DM days to maturity, GFP = grain filling period, PH = plant height, NPBPP = number of primary branches per plant, NPPP = number of pods per plant, NSPP = number of seeds per pod, PC = pod clearance, PL = pod length, PdW = pod width, PdL = peduncle length, NPPPd = number of pods per peduncle, TLL = terminal leaflet length, TLW = terminal leaflet width and NRPP = number of racemes per plant, HSW = hundred seed weight, SL = seed length, ST = seed length, SW = seed width, Yld = seed yield per plot, BM = biomass and HI = harvest index.
and its association with seed yield (rg = −0.25**). In contrast, [
Traits | DF | GFP | DM | PH | PdL | NRPP | NPPpd | TLW | PL | PdW | NSPP | SL | SW | ST | HSW | BM | HI |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | −0.051 | 0.001 | −0.041 | −0.009 | −0.003 | 0.000 | 0.013 | −0.002 | −0.019 | −0.016 | −0.009 | −0.019 | −0.020 | −0.019 | −0.010 | −0.011 | −0.004 |
GFP | 0.001 | −0.036 | −0.021 | −0.002 | −0.003 | 0.004 | −0.002 | −0.002 | 0.001 | 0.001 | 0.001 | 0.000 | 0.001 | 0.001 | −0.001 | 0.000 | 0.000 |
DM | 0.049 | 0.035 | 0.061 | 0.012 | 0.006 | −0.004 | −0.010 | 0.004 | 0.017 | 0.014 | 0.008 | 0.018 | 0.018 | 0.018 | 0.011 | 0.010 | 0.004 |
PH | 0.000 | 0.000 | 0.000 | −0.002 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
PdL | −0.001 | −0.001 | −0.002 | −0.002 | −0.016 | −0.001 | −0.002 | 0.000 | −0.002 | −0.002 | −0.001 | −0.002 | −0.001 | −0.001 | 0.000 | −0.001 | −0.003 |
NRPP | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | −0.001 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
NPPpd | −0.004 | 0.001 | −0.003 | −0.001 | 0.002 | 0.001 | 0.016 | −0.002 | −0.003 | −0.003 | −0.003 | −0.003 | −0.003 | −0.003 | −0.002 | −0.001 | 0.000 |
TLW | 0.000 | 0.000 | 0.000 | 0.001 | 0.000 | 0.001 | −0.001 | 0.005 | 0.001 | 0.001 | −0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 |
PL | 0.008 | −0.001 | 0.006 | 0.001 | 0.002 | 0.003 | −0.004 | 0.003 | 0.021 | 0.010 | 0.006 | 0.011 | 0.012 | 0.012 | 0.004 | 0.006 | 0.006 |
PdW | −0.002 | 0.000 | −0.001 | 0.000 | −0.001 | −0.001 | 0.001 | −0.001 | −0.003 | −0.006 | −0.002 | −0.003 | −0.003 | −0.003 | −0.001 | −0.001 | −0.002 |
NSPP | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | −0.001 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
SL | −0.004 | 0.000 | −0.003 | −0.001 | −0.001 | −0.001 | 0.002 | −0.002 | −0.006 | −0.005 | −0.001 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
SW | 0.001 | 0.000 | 0.001 | 0.000 | 0.000 | 0.001 | −0.001 | 0.000 | 0.001 | 0.001 | 0.000 | 0.002 | 0.003 | 0.002 | 0.001 | 0.001 | 0.001 |
ST | −0.002 | 0.000 | −0.001 | 0.000 | 0.000 | −−0.001 | 0.001 | −0.001 | −0.003 | −0.002 | −0.001 | −0.004 | −0.005 | −0.005 | −0.002 | −0.002 | −0.002 |
HSW | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
BM | 0.122 | −0.006 | 0.094 | 0.012 | 0.054 | 0.064 | −0.021 | 0.054 | 0.170 | 0.139 | 0.079 | 0.187 | 0.193 | 0.193 | 0.018 | 0.583 | 0.179 |
HI | 0.057 | −0.005 | 0.042 | 0.062 | 0.105 | 0.093 | −0.011 | 0.082 | 0.169 | 0.181 | 0.115 | 0.208 | 0.226 | 0.191 | 0.055 | 0.199 | 0.647 |
Residual = 0.122. DM = days to flowering, DM days to maturity, GFP = grain filling period, PH = plant height, NPBPP = number of primary branches per plant, NPPP = number of pods per plant, NSPP = number of seeds per pod, PC = pod clearance, PL = pod length, PdW = pod width, PdL = peduncle length, NPPPd = number of pods per peduncle, TLL = terminal leaflet length, TLW = terminal leaflet width and NRPP = number of racemes per plant, HSW = hundred seed weight, SL = seed length, ST = seed length, SW = seed width, Yld = seed yield per plot, BM = biomass and HI = harvest index.
Generally, the residual effects were low (0.147, 0.212) these indicated that traits which were included in the genotypic path analysis explained 85.3% and 78.8% of the total variation on seed yield at Miesso and Melkassa, respectively, indicating that the independent traits were explained the dependent trait (seed yield) more than two third (2/3); therefore, the genotypic path coefficient analysis based selection for cowpea improvement is very appropriate. [
The results of phenotypic path coefficient analysis of seed yield with other 18 traits at Miesso and Melkassa are presented in
Similarly, at Melkassa, harvest index (0.647) followed by biomass (0.583) and days to maturity (0.061) had exerted positive and favorable direct effect on seed yield. [
Generally, the present investigation suggests that days to maturity, biomass, harvest index, and seed width should be given as the most reliable selection indices for effective improvement in cowpea as the appropriate selection indices. The selection procedure should be formulated so that to proceed in one component is not exposed by the deterioration effect of the other. Therefore, Path analysis indicated that days to maturity, biomass, harvest index and seed width were the main determinants of seed yield. Thus, these traits should be given more emphasis during selection for yield improvement in cowpea.
The present study revealed that the magnitude of the genotypic correlations was higher than the phenotypic correlations in most traits. Traits depict the existence of strong inherent association among traits due to the genetic control. In addition to these, the present study showed the masking effects of the environmental factors were too little. In this study, the results of seed yield showed significant and positive genotypic and phenotypic correlations with length, seed thickness, seed width, hundred seed weight, biomass and harvest index at both locations. This indicated that the traits were significantly important for direct selection. Hence, improving one or more traits could result in high seed yield in cowpea. On the other hand, days to flowering, grain filling period and days to maturity were negative phenotypic and genotypic correlation with seed yield at Miesso. However, days to flowering and days to maturity had positive phenotypic and genotypic correlation with seed yield at Melkassa.
Genotypic path coefficient analysis revealed that days to flowering, biomass and harvest index had relatively high positive direct effect on seed yield at Miesso, and seed thickness, plant height, days to maturity and biomass at Melkassa had relatively high positive direct effect on seed yield. However, seed width and hundred seed weight had exerted negative direct effect on seed yield at each location. At phenotypic path coefficient analysis showed that biomass and harvest index had exerted high positive direct effect on seed yield at both locations. In general, this study clearly stated background information on correlation and path coefficient analysis of seed yield with other yield related traits. Therefore, the present results consider as benchmark information for future high take molecular based analysis and genome wide association study for identifying important traits for cowpea seed yield improvement.
The author would like to thank Melkassa Agricultural Research Center for providing all field work expenses and other research facilities. I would like to express my especial thanks to Sirka Teshome, Samir Hashim, Aliye Tunie and Hekima Hamid for their unlimited support and appreciation.
The authors declare no conflicts of interest regarding the publication of this paper.
Walle, T., Mekbib, F., Amsalu, B. and Gedil, M. (2018) Correlation and Path Coefficient Analyses of Cowpea (Vigna unguiculata L.) Landraces in Ethiopia. American Journal of Plant Sciences, 9, 2794-2812. https://doi.org/10.4236/ajps.2018.913202