Estimation of components of variance through numerical approach in blackgram (Vigna mungo L. Hepper)

Blackgram [Vigna mungo (L.) Hepper, 2n = 2x = 22] is among the most widely cultivated pulses of India. The material for present study comprised of 55 entries including 10 parents namely, Dungla, T9, RBU28, RBU38, TPU4, 99-U-27, RUD79, RUD59, BGU102, BGU54 and 45 crosses were grown in two environments (first (E1), control; second (E2) use of Rhizobium urd culture for seed treatment) were planted in single row plot of 2 meter length with 30 and 10 cm row to row and plant to plant spacing, respectively in randomized block design with three replications during kharif, 2000 at Plant Breeding Farm of Rajasthan College of Agriculture, Udaipur. Observations were recorded under two heading A-traits related to nitrogen fixation and B phenological and developmental traits. Validity of assumptions of diallel analysis were tested by ‘t²’ and regression coefficient ‘b’. In the present study the assumptions were satisfied for nodules fresh weight per plant in both environments E₁ and E₂, nodules dry weight per plant only in E₂, days to 50% flowering in both E₁ and E₂, 100-seed weight only in E₁, harvest index only in E₁ and nitrogen content of straw in both E₁ and E₂. While for other characters assumptions of diallel were not satisfied. The components additive (D) and dominance (H₁ and H₂) were significant for all those characters where assumptions were satisfied indicating importance of both additive and non additive components in the inheritance of these traits. The magnitude of dominance (H₁) was significantly higher than additive components (D) for days to 50% flowering in both E₁ & E₂, nodules fresh weight per plant in both E₁ & E₂, nodules dry weight per plant in E₁ and harvest index in E₁ exhibited the presence of over dominance and it is also supported by the ratio of ²SCA: ² GCA that was greater than one for the same characters. Whereas, nitrogen content of straw in E₁ & E₂ registered higher additive component. Additive and non additive component had equal variance for 100-seed weight in E₁ indicated the complete dominance. uv ratio estimated was approximately equal to maximum expected value for nodules fresh weight per plant in E₁ and E₂, nodules dry weight per plant in E₂, days to 50% flowering in E₁ & E₂, 100-seed weight in E₁ suggested the frequencies of positive and negative genes were distributed equally between the two parents. Whereas uv ratio for nitrogen content of straw in E₁ & E₂ showed asymmetrical distribution of positive and negative genes among parents. The covariance between additive and dominant effect (F component) was non-significant for all the traits (satisfied the assumptions of diallel) revealed equal distribution of recessive and dominant alleles among the parents further strengthed by u/v ratio. Similar genetic control was exhibited by the order of dominance (Wr + Vr) and array per se performance (Yr) relationship which indicated that all the studied traits determined by equal proportion of dominant and recessive genes except nodules dry weight per plant, that determined by dominant genes. The heritability in narrow sense was significant for nitrogen content of straw 74.48% (E₁) and 73.33% (E₂), 100-seed weight 64.36%, nodules fresh weight per plant. 56.76% in E1 and 56.75% in E2 and nodules dry weight per plant 49.74% indicating predominance of additive gene action. From the above discussion for gene actions it is clear that both additive and non-additive components were involved is the expression at the above-mentioned traits. The magnitude of dominance component was higher except nitrogen content of straw where additive component was higher.