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.
Blackgram (Vigna mungo L.), Components of variance and Nitrogen fixation
