Genetic Studies on Seed Coat Texture And Cooking Time in Some Varieties of Cowpea (Vigna unguiculata (L.) Walp.)

ABSTRACT

Genetic studies on seed coat texture and cooking time in some varieties of cowpea (Vigna unguiculata (L.) Walp.) were carried out between August 14, 2000 and November 20, 2002 and August 2, 2001 and December 3, 2003 respectively. The experiments were carried out at the research and teaching farm, Federal University of Technology, Yola, Adamawa State. Randomized complete block design with five replications was used for the two experiments. Appropriate crosses were made among eight cowpea varieties with four types of seed coat texture in order to study inheritance pattern of seed coat texture. Seed coat texture was observed to be controlled by two gene pairs with various forms of gene interactions such as dominance and recessive epistasis. Complete dominance of smooth seed coat texture over wrinkle, rough and loose seed coat textures was observed. Wrinkle seed coat texture plants also show complete dominance over rough and loose seeded plants. Recessive epistasis was observed in the cross between rough seed coat texture and loose seed coat texture. The genes that controlled smooth, wrinkle, rough and loose seed coat textures were all nuclear and cytoplasmic genes had no effect on seed coat texture. The progenies of reciprocal crosses between two long and one short cooking time varieties that were found to be significantly different among the eight cowpea varieties were evaluated in a field study to determine the mode of inheritance of cooking time in cowpea. The generation mean analysis adopting the additive-dominance model was not adequate for explaining the mode of inheritance of cooking time in cross TVu 39 (long cooking time) x TVu 14195 (short cooking time) and TVu 803 (long cooking time) x TVu 14195 (short cooking time) due to the xvi involvement of non-allelic interactions in the inheritance of seed cooking time, but adequate for cross TVu 39 (long cooking time) x TVu 803 (long cooking time). However, the six-parameter model with epistatic gene interactions was adequate for explaining the inheritance of seed cooking time. Frequency distribution of F2 and backcross populations shows that the trait is quantitatively inherited. Two dominant alleles operating at different loci controlled cooking time trait in the cowpea varieties studied. Although gene action was predominantly dominance, additive and all epistatic gene effects were also significant. Short cooking time was dominant over long cooking time. The genes that controlled cooking time were all nuclear and cytoplasmic genes had no effect. There was transgressive segregation in cooking time and this may suggest that a new variety having very short cooking time could be selected at advanced generation. Broad and narrow sense heritability estimates were high (89%-95% and 58%-85% respectively). Genetic advance under selection with 5% selection intensity was 4.69 and 3.77 minutes for cross TVu 39 x TVu 14195 and TVu 803 x TVu 14195 respectively, suggesting that progress could be made in breeding for short cooking time. The large genotype effect of cooking time coupled with the high heritability suggests that selection based on the trait itself may allow for progress in breeding.