Cowpea rust fungus affects photosynthetic rate and physiological performance of the host plant through the induction of structural changes in the host cell. The study assessed the effects of rust fungus onnet photosynthetic efficiency and yield performance of cowpea genotypes under field conditions. The experiment was conducted in the minor cropping season following a randomized complete block design outlay with three replications. Chlorophyll fluorescence of healthy leaves and rust-infected leaves of each cowpea genotype was determined by a non-destructive method.Rust disease severities of the infected leaves were assessed based ona diagrammatic scale. The effect of rust on the net photosynthetic rate was quantified by the model Px / Po = (1 – x)β. Growth and yieldtraits of the cowpea genotypes and correlation between seed yield and photosynthetic efficiency were determined. The cowpea genotypes responded differently to rust infection as expressed in net photosynthetic rates,growth, and yield. The pathogen impaired photosynthetic efficiency of leaf tissue beyond the observed diseased leaf area. Seed yield was more closely related to the βestimate than that observed for the relative net photosynthetic rate.
The demand for resistance cowpea to rust infection has currently increased due to considerable yield losses caused by the fungal pathogen. The study assessed available cowpea genotypes for rust resistance using simple sequence repeat (SSR) markers. Out of 100 cowpea genotypes screened, 97% showed presence of the markers whilst 3% showed absence of the markers. Among the cowpea were 72% resistance, 16% moderate resistance and 9% low resistance to rust. The markers revealed mean high allele frequency (0.86) and low gene diversity (0.24) and polymorphism information content (0.21) among the cowpea genotypes. The markers co-inherited with mean regression value greater than 0.1. There was no clear pattern of clustering among the cowpea genotypes. The cowpea genotypes with rust resistance traits could serve as good sources of germplasm for cultivation or resilient genes with rust target in breeding programmes to improve the crop.
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