Abstract: Components of genetic variation for pod yield and other associated yield characters in lablab bean have been estimated through six-parent diallel cross in F2 generation. Additive as well as dominance components were significant for all the characters in both environments. Diallel analysis after Hayman’s approach suggested environmental interaction for flowering date, pods/inflorescence, inflorescence/plant and pod yield/plant. Complete dominance was observed for flowering date in environment 2, flowers/inflorescence and pod yield/plant in environment 1 and pods/inflorescence, pod width in both environments. Over dominance was displayed for flowering date in environment 1 and for pod yield/plant in environment 2. Partial dominance was found for flowers/inflorescence in environment 2 only but for inflorescence/plant, pod length and 10-pod weight in both environments.
Introduction
Lablab bean is a protein rich major winter. vegetable in different parts of Asia. Many types and varieties of lablab bean are found in Asia. Little research work has been done to improve its pod yield and other associated characters. Work on genetic improvement of this crop is mainly done in India (Baldev et al., 1988), but not much studies on genetic architecture.
The improvement of yield depends on a better understanding of the type of gene action. Evaluation of genotype performance in different environments is important in plant breeding. Genetic studies on lablab bean have been reported by some investigators (Mia et al., 1989; Ushakumari and Chandrasekharan, 1992; Newaz et al., 1995; Arora and Loodhi, 1998). The differential response of genotypes when subjected to different environments possess a major problem relating phenotypic performance to genetic constitution and make it difficult to decide which genotype should be selected. It is important to understand more fully the nature of genotype x environment (GXE) interaction to make testing and selection of genotypes more efficient. The present investigation about the nature arid magnitude of the components of variation yield and its direct components would be helpful in deciding the most efficient breeding procedure in Lablab purpureus.
Materials and Methods
Six genotypes of lablab bean were crossed in all possible combinations excluding reciprocals in Bangladesh Agricultural University Farm at Mymensingh. Seeds of parents and 15 F, families were shown with five replications in RCB design. Two cultural environments lenv.1 was with fertilizer and early sowing and env. 2 was without added fertilizer but had relatively latter sowing date were considered to investigate environmental interaction in the study. Sowing distance was 2 m x 2 m, between and within the rows. Diallel analysis was done following Hayman (1954a,b) approach. The genetic components of variation in F2 population were calculated according to Jinks (1956) and heritability was estimated as outlined by Verhalen and Murray (1969) for population.
Results and Discussion
From the Hayman analysis of variance (Table 1) environmental heterogeneity was found for additive (a) genetic effect in inflorescence/plant and pod yield/plant for dominant (b) genetic effect in pods/dnflorescence and for both in flowering date. In both the environments, additive and dominant genetic eornpononts were important in the regulation of almost all the characters except inflorescence/plant and 10-pod weight in environment 2 which showed good agreement with Table 2. Although additive genetic components preponderance in inflorescence/plant, pod length and pod yield/plant, environmental interaction was observed only pod yield/pant for additive component. Environment could not influence upon Flowers/inflorescence, pod length, pod width and 10- pod wt.
Table 2 suggested that in majority of the characters, excess dominant allele was present in their parents except inflorescence/plant, pod length and pod yield/plant because their F value was positively significant. For all the characters differences between parents and crosses were present, which is measured by h value. Degree of dominance was measured by (H1/D)/4) parameter. Complete dominance was observed in pods/inflorescence and pod width for both environments, in flowering date for environment 2, in flowers/inflorescence and pod yield/plant for environment 1.
| Table 1: | Hayman analysis of variance following Morley Jones modification for eight plant characters in a 6 x 6 dial experiment on Lablab bean conducted in two environments |
| *p<0.05; **p<0.01; ***p<0.001 | |
In both environments, inflorescence/plant, pod length, 10-pod weight and in environment 1, flowers/inflorescence was controlled by partial dominance. Partial dominance was also reported by Jacob (1983) for flowers/inflorescence, inflorescence /plant and pod yield/plant whereas Khondker (1995) for pods/ inflorescence, pod length and 10-pod weight in lablab bean. Over dominance was found only flowerings date in environment 1 and pod yield/plant in environment 2. Singh et al. (1986) reported over dominance in lablab bean for flowering date. All traits were governed by asymmetrical distribution, of positive and negative alleles. Positive and negative alleles were in equal proportion in the parents for yield character as H2/4H1 values were 0.25 and 0.2 environment 1 respectively. Unequal distributions dominant and recessive genes were observed for all characters except pod yield/plant. Dominant and reces were equally distributed in yield character because [v(4DH1)/4+F/2]/(4DH1)/4-F/2] ratio was nearly equal unity. Gene group present in the parent of different treatment governed by h2/H2. One or two genes or gene groups v involved in all traits. High narrow sense heritability observed in pods/inflorescence, pod length and 10-pod weight. High broad heritability was in flowering day flowers/inflorescence, pod length and 10-pod weight. Joshi (1971) and Reddy (1982) also reported high heritability pods/plants inflorescence and Nayer (1984) for 10-pod were Heritability was moderate in both sense for pod yield/plant Gangadharappa (1981) also found that in lablab bean.
| Table 2: | Components of variation and genetic parameters for eight plant characters from a 6 x 6 diallel experiment oh Lablab bean conducted in two environments |
Acknowledgments
Author gratefully acknowledge the award of an NST fellowship by the Ministry of Science and Technology, Govt. of Bangladesh, and the provision of field research facilities extended by Bangladesh Agricultural University authority.