Yield is a complex trait as many component traits contribute towards it. Being a quantitative trait in nature it is affected by genotype (G) × environment (E) interactions. Hence to bring change in yield, deep understanding of extent of variability present in a population and also interrelationship among yield and yield attributing characters is necessary. The analysis of variance (ANOVA) carried out for BC
1F
3 and F
3:4 generations indicated significant genotypic variation for all the traits in both the generations (Table 1).
Genetic variability
Phenotypic coefficient of variation (PCV) estimates was higher than the respective genotypic coefficient of variance (GCV) for all the traits under study, indicating the influence of environment in the expression of these traits. Wide range of phenotypic variation was observed in BC
1F
3 and F3:4 generations (Table 2). In BC
1F
3, the highest value of PCV was observed for pods per plant (33.63%) followed by seed yield per plant (33.12%) and fruiting branches per plant (30.72%). The highest value of GCV was observed for pods per plant (31.25%) followed by seed yield per plant (30.26%) and fruiting branches per plant (28.61%). The low GCV was observed for traits like 100-seed weight (8.37%), plant height (6.16%), days to 50 per cent flowering (5.52%), days to maturity (4.89%) and seeds per pod (3.98%) in BC1F3. While in F3:4 generation, the highest value of PCV was observed for seed yield per plant (51.34%) followed by pods per plant (44.47%) and fruiting branches per plant (37.05%). The highest value of GCV was observed for seed yield per plant (47.40%) followed by pods per plant (40.83%) and fruiting branches per plant (33.47%) in F
3:4 generation. It was interesting to note that extent of variability was reduced in BC
1F
3 as compared to F
3:4 generation, which was probably due to reduction of wild genome as a result of one backcross. Generation of abundant variability for these traits is generally expected in the inter-specific crosses in pigeonpea as earlier reported by
Bohra et al., (2015). Presence of variability for different traits was also reported by
Bhadru (2010),
Sharma et al., (2012), Rangare et al., (2013), Singh et al., (2014), Ram et al., (2016), Mallesh et al., (2017), Reddy and Jayamani (2019) and
Watsal (2019) in cultivated pigeonpea. Above results suggested that due to higher values of PCV and GCV for pods per plant, fruiting branches per plant and seed yield per plant in both the generations, the selection will be more effective for these traits in subsequent generations for improving yield.
Heritability and genetic advance
Perusal of Table 2 indicated high estimates of heritability for fruiting branches per plant (86.76%), pods per plant (86.35%) and seed yield per plant (83.48%), whereas moderate heritability was recorded for days to maturity (76.52%), days to 50 per cent flowering (74.46%) and plant height (66.89%) in BC
1F
3 generation. The highest heritability in F
3:4 was recorded for days to 50 per cent flowering (87.36%) followed by seed yield per plant (85.24%), days to maturity (84.82%), pods per plant (83.17%) and number of fruiting branches per plant (81.59%). Whereas, for plant height (63.27%), seeds per pod (62.50%) and 100-seed weight (53.00%), moderate heritability was recorded. Similar findings were reported by
Sharma et al., (2012), Rangare et al., (2013), Nagy et al., (2013), Reddy and Jayamani (2019) in cultivated pigeonpea and by
Bohra et al., (2015) in interspecific crosses in pigeonpea.
The highest genetic advance was recorded in BC
1F
3 generation (Table 2) for pods per plant (59.82%) followed by seed yield per plant (56.96%), while the lowest genetic advance was recorded for seeds per pod (5.37%). However, in F
3:4 generation, the highest estimate of genetic advance was recorded for seed yield per plant (90.11%) followed by pods per plant (76.70%), while seeds per pod recorded the lowest genetic advance (12.30%). Present results were in confirmation with results obtained by
Patel et al., (2011), Prasad et al., (2013), Rao et al., (2013), Shunyu et al., (2013), Meena et al., (2017) and
Watsal (2019) who also obtained high genetic advance for pods per plant and seed yield per plant in cultivated pigeonpea.
In both the generations, high heritability coupled with high genetic advance for fruiting branches per plant and pods per plant revealed that these two traits are important yield components and selection should be focused on these for yield improvement. These results revealed the presence of low environmental influence and prevalence of additive gene action in the expression of these traits. Moderate or low heritability estimates coupled with low genetic advance were recorded for seeds per pod and 100-seed weight indicating that these traits were governed by non-additive gene action and highly influenced by environment so direct selection would not be effective for improving yield.
Association studies (correlation and path analysis)
Correlation analysis clearly revealed that the phenotypic and genotypic correlations have similar trend in direction but the magnitude of genotypic correlations was higher than the phenotypic correlations. Low phenotypic correlation could be the result of masking and modifying effect of the environment on the association of traits. Correlation coefficients among all the traits in BC
1F
3 generation presented in Table 3. Seed yield per plant had significantly high and positive correlation with pods per plant (0.92) followed by fruiting branches per plant (0.85), 100-seed weight (0.52) and seeds per pod (0.32).
Sinha and Singh (2005),
Baskaran and Muthiah (2007),
Prasad et al., (2013), Pandey et al., (2016), Pushpavalli et al., (2017) and
Baldaniya et al., (2018) also found significant and positive correlations between seed yield per plant and number of pods per plant. In F
3:4 generation, results also showed highly significant and positive correlation of seed yield per plant with pods per plant (0.88) followed by fruiting branches per plant (0.85) and seeds per pod (0.41). Similar, results were reported by
Singh et al., (2018) in BC
1F
2 and F
2:3 generations of the same cross for fruiting branches and pods per plant which indicated that correlations of traits remained consistent in different generations. An overall observation of correlation coefficient analysis revealed that fruiting branches per plant and pods per plant showed positive correlation with seed yield per plant. Hence, direct selection for these traits will be quite effective to improve yield in pigeonpea. It was interesting to note that days to 50% flowering showed significant negative correlation with fruiting branches, pods per plant, 100-seed weight and seed yield per plant in BC
1F
3 population, while in F
3:4 generation, these correlation were very low or non-significant. Similarly, days to maturity showed significant negative correlation with seed yield per plant in BC
1F
3 generation, while in F
3:4 these correlations were very low or non-significant. This indicated that selection for high yield should be focused on early flowering and early maturity plants in segregating progenies where one backcross has been performed while in F
3:4, selection for both early and late maturity can be done without sacrificing yield.
Correlation simply indicates the types of relationship among the characters but does not provide information on extent of relationship (direct or indirect effect). Path coefficient analysis was carried out to understand the extent of relationship by taking seed yield per plant as dependent variables and rest of the traits as independent variables. At phenotypic level in BC
1F
3 generation (Table 4), the highest direct effect on seed yield per plant was exerted by pods per plant (0.482) followed by fruiting branches per plant (0.344) and 100-seed weight (0.318). Whereas, the plant height (-0.082) and days to maturity (-0.065) showed negative direct effect on the seed yield per plant. Indirect positive effects on seed yield per plant were revealed by number of fruiting branches per plant (0.463), 100-seed weight (0.131) and seeds per pod (0.063) via pods per plant. In F
3:4 generation, pods per plant (0.818) exhibited the highest direct effect on seed yield per plant followed by 100-seed weight (0.285) and seeds per pod (0.195), While fruiting branches per plant (0.783), plant height (0.204), seeds per pod (0.186), days to 50 per cent flowering (0.131) and days to maturity (0.120) exerted indirect positive effect on grain yield per plant via pods per plant. Similar findings were reported by
Thanki and Sawargaonkar (2010),
Devi et al., (2012), Chaithanya et al., (2014), Vijayalakshmi et al., (2013), Chandana et al., (2014), Kothimbire et al., (2016), Ram et al., (2016), Kumar (2017) and
Ranjani et al., (2018) in pigeonpea. Hence, in both generations direct selection for the pods per plant and fruiting branches per plant could be effective in developing high yielding genotypes in pigeonpea.