Aggressiveness of diverse African isolates of Cercospora zeina on maize

Abstract

Cercospora zeina the causal agent of grey leaf spot of maize causes up to 67% yield losses when susceptible maize cultivars are planted. Variations in the levels of aggressiveness of C. zeina isolates have been reported previously. However, none of the previous studies links the variation in their levels of aggressiveness to the genetic diversity. This study links the genetic diversity within and between African populations of C. zeina isolates to differences in aggressiveness. In this study, the variation in the aggressiveness of five C. zeina isolates (CEDV05074, CMW25467, ZWRRS263, UGKPC38, and KEKER468) was assessed using six quantitative traits namely, incubation period, infection efficiency, lesion size, disease severity index (DSI), area under disease progression curve (AUDPC) and sporulation capacity. Our findings reveal that the genetic diversity previously observed in the C. zeina isolates influences their level of aggressiveness. From this study, we noted the need to standardize the protocol for assessing the infection efficiency and the timing for measuring lesion size in the maize-C. zeina pathosystem. Our findings also proved that hybrid-3 was the most susceptible hybrid and therefore will be used for future aggressiveness assays. Lastly, the identity of the five C. zeina isolates was confirmed using four molecular tools namely, CTB7 gene region, mating type genes, internal transcribed spacer (ITS) gene region, and microsatellite markers. Overall, this study is a step towards mechanisms involved in the pathogenicity of C. zeina. Furthermore, using isolates with high aggressiveness is key for maximizing selection gain when using artificial inoculation to assess maize plant resistance to GLS disease.