Relationships between Hybrid Performance and Genetic Distance Revealed by Morphological and Molecular Markers in Cowpea (Vignaunguiculata (L.) Walp)

Abstract

The genetic diversity and relationships among six cowpea (Vigna unguiculata) genotypes were evaluated using 10 agro-morphological traits and two molecular marker systems ISSR and SRAP. The phenotypic distance (PD) among all genotypes was relatively high. ISSR markers were more efficient than SRAP with regards to polymorphism detection, average number of polymorphic-bands per primer (PB), resolving-power (RP), marker-index (MI) and polymorphism-information-content (PIC). ISSR and SRAP markers were generated cultivar or genotype specific unique DNA fingerprints able to identify the most diverse genotypes. The Dic genetic similarity ranged from 0.744 (P1 and P4) to 0.868 (P2 and P3). A positive correlation was found between ISSR and SRAP markers as well as between molecular markers and phenotypic markers. Based on phenotypic distance (PD) and genetic distance (GD), six parents of cowpea were crossed in half diallel fashion in order to determine combining ability to identify promising hybrids for ten traits including yield and its components. The both additive and non-additive effects of the controlling genes were involved in the inheritance of the traits studied. High broad-sense heritability estimates were obtained for all the traits as well as the narrow-sense heritability was larger than 0.60 in time to 50 % flowering, pod length, weight of pods per plant, weight of seeds per plant and total dry seed yield, so selection for these traits could be useful. The adequacy of additive-dominance model was fit for time to 50 % flowering, number of branches per plant, weight of pods per plant, weight of seeds per plant and total dry seed yield, while non-allelic gene interaction was observed for pod length, number of seeds per pod and pod diameter. The estimates of general combining effects revealed that P5 had the highest positive and significant values for number of pods per plant, weight of pods per plant, weight of seeds per pod and total dry seed yield while P1 exhibited the lowest negative and significant GCA for number of pods per plant, weight of pods per plant, weight of seeds per pod and total dry seed yield. The highly significant correlations were found between total dry seed yield and number of pods per plant (0.87), weight of pods per plant (0.95) and weight of seeds per plant (0.95). Mating designs used in this study were suitable for studying genetic parameters in cowpea. The high values of broad-sense and narrow-sense heritability indicated a good genetic variability for effective selection. The relationship between phenotypic and genotypic distance as well as the heterosis and SCA were estimated. Results indicated that the genetic distance was positive and/or negative and significantly correlated with some traits, while it was not significantly correlated with effects of heterosis and SCA for some other traits. Our results noted that knowledge about the genetic distance between parents can be used to predict hybrids performance.