Evaluation of Ugandan cowpea germplasm for yield and resistance to scab disease

Aims: This study was conducted to identify cowpea (Vigna unguiculata) cultivars with high yield potential and resistance to scab disease caused by Sphaceloma sp. in Uganda. 100 cowpea genotypes were evaluated at two locations (Kabanyolo and Serere) in Uganda between April and July, 2014 using a 10 × 10 alpha lattice design. Place and Duration of Study: Makerere University Agriculture Research Institute - Kabanyolo (MUARIK) and the National Semi Arid Resources Research Institute (NaSARRI) – Serere between April to July, 2014. Study Design and Methodology: Hundred cowpea lines (69 landraces, 25 inbred lines at F7, 1 local and 5 improved cultivars) were grown at each location in a 10 × 10 alpha lattice design with 3 replications to assess their reaction to the scab disease and yield potential (grain yield and yield related traits). Results: The cowpea lines differed significantly (P = .05) in their response to natural disease pressure as determined by disease incidence, apparent infection rate (r) and severity indicated by area under disease progress curve (AUDPC). Analysis of variance showed that there was highly significant differences (P < .001) in genotypes, locations, AUDPC and other traits and genotype by location (G×L) interaction on AUDPC. The correlation analysis revealed a positive relationship of scab disease incidence with AUDPC (0.8; P < .001) but a significant (P < .001) negative relationship with grain yield (-0.8), number of pods per plant (-0.5), number of seeds per pod (-0.5) and 100 seed weight (-0.5). Cluster analysis based on only scab disease indexes produced 4 main clusters while cluster analysis based on disease and yield traits produced 3 main clusters. However, the two different clusters revealed similar grouping patterns in which cowpea lines with similar resistance ratings were shown to form unique clusters. R-mode principal component analysis yielded 4 principal components explaining 62.28% of the variation observed. Conclusion: The study revealed that the use of apparent infection rate “r” alone as an index for rating a genotype for scab reaction was not decisive. One line (NE 15) was found to be resistant to the scab disease at both locations and high yielding and could be used in the cowpea improvement programme to breed for resistance to the scab disease.