Identification of resistant cowpea genotypes and aggressiveness of Macrophomina phaseolina isolates by diallel analysis

Abstract

Cowpea is grown in semiarid regions of Brazil. However, the occurrence of diseases, such as charcoal rot, is one of the main limiting factors to production. Disease is caused by the fungus Macrophomina spp., one of the most important plant pathogens in semiarid conditions. The use of resistant cultivars is the most effective method to control this disease. The objective of this study was to evaluate cowpea lines inoculated with different Macrophomina phaseolina isolates to determine the aggressiveness of the pathogen isolates and the predominant type of resistance in the host. The experiment was carried out in a completely randomized design, using a 5 × 10 factorial scheme with five replications (two plants per pot) in two independent crops. Partial diallel analysis was used to assess the reaction of host genotypes (horizontal and vertical resistance) and the aggressiveness of the isolates. Host reaction and pathogen aggressiveness were analysed by lesion length. Horizontal resistance was observed, corresponding to 56.69% of the variation. The lines L19, L29, L48, and L95 were the most resistant based on estimates of general responsiveness. Among the M. phaseolina isolates evaluated, N105 and ISO16 were the most aggressive based on general aggressiveness ability. By diallel analysis, we identified the most promising genotypes, as well as the most aggressive isolates.