Resistance to Ascochyta phaseolorum and Multivariate Analysis of Mutational Derived Cowpea Lines

Cowpea plays a vital role in diets of many households, primarily as a source of protein. Among the biotic stresses Ascochyta blight caused by Ascochyta phaseolorum reduces cowpea yields among the small-scale farmers. The University of Zambia (UNZA), developed cowpea derived mutational lines as a way of increasing genetic diversity among cowpea germplasm in the country. The objective of this study, was therefore i) to identify resistant cowpea mutational derived genotypes to Ascochyta phaseolorum, ii) to cluster cowpea genotypes into distinct groups and iii) identify the best parental set to utilize as a cross in a further breeding program. The experiment was laid at the University of Zambia and Mt Makulu as a randomized complete block design (RCBD) with three replications It was artificially inoculated with Ascochyta phaseolorum. Significant differences (P = 0.001) were obtained among genotypes with regards to disease severity score. The genotypes, BB 8 –1 - 5- 2, LT 4 -2- 4- 1, LT 11- 3 -3- 12 and MS 1- 1 -8 – 4 were identified as resistant genotypes to Ascochyta phaseolorum and also obtained higher yield than the genotypic mean value. In this study, principal component analysis revealed six distinct groups of cowpea genotypes. Detailed analysis revealed that a genotypic cross, LT 11-3-3-12 (From group A) x BB PRT (from group E) were most dissimilar genotypes with a similarity score level of 30.3 %. Thus, this cross (LT 11-3-3-12 x BB PRT) is expected to segregate and exhibit highest phenotypic variation in advanced generations.