Variation in the morphology and effector profiles of Exserohilum turcicum isolates associated with the Northern Corn Leaf Blight of maize in Nigeria

Abstract

Background Maize production in lowland agro-ecologies in West and Central Africa is constrained by the fungus Exserohilum turcicum, causal agent of Northern Corn Leaf Blight (NCLB). Breeding for resistance to NCLB is considered the most effective management strategy. The strategy would be even more effective if there is adequate knowledge of the characteristics of E. turcicum in a target region. Maize leaves showing NCLB symptoms were collected during field surveys in three major maize growing areas in Nigeria: Ikenne, Ile-Ife, and Zaria during 2018/2019 and 2019/2020 growing seasons to characterize E. turcicum populations interacting with maize using morphological and molecular criteria. Results A total of 217 E. turcicum isolates were recovered. Most of the isolates (47%) were recovered from the Ikenne samples while the least were obtained from Zaria. All isolates were morphologically characterized. A subset of 124 isolates was analyzed for virulence effector profiles using three primers: SIX13-like, SIX5-like, and Ecp6. Inter- and intra-location variations among isolates was found in sporulation, growth patterns, and presence of the effectors. Candidate effector genes that condition pathogenicity and virulence in E. turcicum were found but not all isolates expressed the three effectors. Conclusion Morphological and genetic variation among E. turcicum isolates was found within and across locations. The variability observed suggests that breeding for resistance to NCLB in Nigeria requires selection for quantitative resistance to sustain the breeding efforts.