Estimation of heritability and genetic correlation is the basis for assessing the efficiency of indirect selection for yield contributing traits as against direct selection for grain yield. These parameters vary with the advancement of segregating generations. They need to be estimated for each segregating generations separately. But, estimation of these parameters for each generation in different season is influenced by environmental factors. Therefore, in the present study all the four segregating generations (F
2, F
3, F
4 and F
5) were evaluated in the same season to avoid varied environmental effect on the expression of traits in different generations. The comparison of mean values for the traits under study in four segregating generations revealed higher values for number of pods per plant, seeds per plant and seed yield in F
3 generation (Table 1). In general mean values for these traits increased from F
2 to F
3 generation and decreased in subsequent generations. On the other hand for seed weight, the mean values remained constant in early segregating generations. Similar report was made by
Salimath and Patil (1990). They evaluated F
3 and F
4 generations in the same season and observed an increase of pods per plant in F
4 when compared to F
3 generation, whereas it remained constant for seed weight.
Shivakumar et al., (2013) evaluated F
2 and F
3 generations in two different seasons (
Rabi 2009-10 and 2010-11). They reported that there was no change in number of pods per plant and seeds per plant in F
2 and F
3 generations but the seed weight increased in F
3 when compared to F
2 generation. The contradictory results of present study and the study reported by
Shivakumar et al., (2013) may be because they advanced only promising segregants from F
2 to F
3 and evaluation of two generations in two different seasons.
Decision on early segregating population cannot be based on only mean values of the traits. Because, selection based on the mean value of the early segregating generations does not provide the range and distribution pattern within each population (
Welsh, 1981). In populations rejected on their mean value, low frequency of high yielding individuals may be lost. Therefore, range of variation and coefficient of variation are the two parameters, which needs to be considered in assessing the early segregating generations. The range of variation for pods per plant and seed yield showed an improvement in F
3 over F
2 (Table 2). With the advancement of generations, the number of progenies with lower value increased for all the traits and progenies with upper value decreased leading to reduction in range of variation. As result frequency distribution of all the traits was skewed towards higher value in F
2 generation, normal distribution in F
3 generation and in F
4 and F
5 generation the distribution was narrowed down to only few classes. The reduction in lines with upper values for these traits is expected as these are the quantitative traits and may be governed by dominance variance. The other reason may be, as there is no selection pressure is applied the low frequency of lines with higher values for these traits may be lost in subsequent generations. However, for seed weight the higher value remained constant in all the generations. Similar results were reported for seed weight by
Salimath and Patil (1990). The contradicting reports were made by
Shivakumar et al., (2013), wherein they rejected less productive lines and advanced only promising lines to F
3 generation. The variability (CV) for all the traits decreased with the advancement of generation. This can be attributed to presence of dominance variance in governing these traits, which is decreased with increase in the homozygosity. The extent of variability is indicative of possibility of application of selection pressure on the population. However, effectiveness of selection on the performance of progenies in the subsequent generation depends on the heritability of the trait. The heritability values in all the four generations calculated by the regression method revealed seed weight to be a highly heritable trait, while seeds per plant and number of pods per plant were moderately heritable. The seed yield per plant showed least heritability in all the generations. With the advancement of generation the heritability decreased for seed weight, increased for number of pods per plant and number of seeds per plant, while remained low and constant for seed yield per plant (Table 3).
Lupton and Whitehouse (1957) suggested that in self pollinated cereals, selection in the early generations should be restricted to traits which are highly heritable. This suggests that selection can be practiced for seed and pod traits in F
3 and F
4 generations.
Bisen et al., (1985) suggested that selection for seed size bulk procedure proved to have advantage over other methods of selection aimed at the genetic improvement of chickpea for seed yield.
The association among the traits suggests that, in all the segregating generations (F
2, F
3, F
4 and F
5) seed yields were obtained with more number of pods per plant, seeds per plant and seed weight. Generally, indirect selection has only been successful where the heritability of the target trait (Seed yield) is very low and heritability of associated traits is high. Considering the variability and heritability of the traits in different generations, it could be concluded that, selection for seed weight in F
2 generation, pod and seed number in subsequent F
3 and F
4 generation may contribute for genetic improvement for seed yield. Parents in the present study differed for seed weight and seed number. Seed weight is a critical trait, which showed positive and significant association with seed yield and other yield contributing traits in F
2 generation. With the advancement of generation, its association with pod and seed number plant decreased and showed negative association with pods per plant in F
5 and seeds per plant in F
4 and F
5 generations. The changes in the correlation between the traits from generation to generation may be due to high degree of segregation and genetic heterozygosity, which leads to breakdown and formation of new linkages (
Kishore and Gupta, 2002). The high seed weight with high seed number is the desirable combination for yield improvement. Therefore simultaneous improvement of seed weight, seed number and seed yield could be achieved by selection for seed weight in F
2 and seed number in subsequent generations.
The inter-generation correlation study showed significant association between F
2-F
3, F
3-F
4 and F
4-F
5 for seeds per plant and seed weight (Table 4). In general inter-generation correlation was low and insignificant for seed yield in all the generations. For other traits, it was high in F
3-F
4 and F
4-F
5 when compared to F
2-F
3. The extent of inter-generation correlation for seeds per plant and pods per plant increased with the advancement of generation. For both the traits correlation between F
4 and F
5 generations is more than the correlation between F
3-F
4 and F
2-F
3 generations. On the other hand high inter-generation correlation was observed for seed weight between F
3 and F
4, compared to F
2-F
4 and F
4-F
5 generations. High estimates of inter-generation correlations between F
3-F
4 and F
4-F
5 indicate that early generation selection for pods per plant, seeds per plant and seed weight should be preferably done in F
3 or F
4 generations.
Rahman and Bahl (1986) also observed that, inter-generation correlation was high in F
3 and F
4 generation for seeds per plant and seed weight.
Kumar and Bahl (1992) concluded that, high yielding lines could be obtained by selection for pod number and seed weight in four successive segregating generations (F
2-F
5). The high estimates of inter-generation correlation for number of seeds per plant and seed weight were recorded between F
3 and F
4 generation. Hence the simultaneous improvement of seed number and seed weight could be effective if selection for both the traits is done in early segregating generation.
Correlations between two generations apart (F
2-F
4, F
3-F
5) were lower than between consecutive generations. The correlations estimated for two generations apart that is between F
2-F
4 and F
3-F
5 was significant for seeds per plant and seed weight. Similarly the correlations between three generations apart was estimated (F
2-F
5) and it was very least and non-significant for all the traits. The estimation of genetic and statistical parameters and also frequency distribution for pod and seed traits suggests that, improvement of seed yield through improved number and seed weight is possible by selection at early segregating generation. Wherein initially the lines with high seed weight should be selected then in subsequent generation, lines with higher seed number should be given emphasis.