Diversity and Mycotoxin Production Potential of Fusarium Species on Maize Ears in South South Nigeria

Fusarium ear rot is a significant pre-harvest disease of maize in the high-humidity South South zone of Nigeria, with implications for fumonisin, zearalenone, and deoxynivalenol mycotoxin contamination of grain entering food and feed supply chains. The diversity of Fusarium species responsible for ear rot and their mycotoxin production profiles in South South Nigeria have not been systematically characterised. This study examined Fusarium species diversity and mycotoxin production potential on maize ears from 75 farms across Rivers, Delta, Bayelsa, and Cross River States over two growing seasons. Morphological and molecular characterisation using translation elongation factor, beta-tubulin, and calmodulin gene sequences identified seven Fusarium species, with F. verticillioides as the predominant species, accounting for 52 percent of isolates, followed by F. proliferatum at 24 percent and F. graminearum at 12 percent. Fumonisin B1 and B2 production was assessed in vitro using high-performance liquid chromatography, and trichothecene chemotype profiling was performed on F. graminearum isolates using chemotype-specific polymerase chain reaction. Fumonisin contamination above the Codex Alimentarius maximum limit was detected in 38 percent of grain samples, with the highest contamination levels in farms experiencing delayed harvest due to waterlogging. All F. graminearum isolates were chemotyped as 15-ADON producers, suggesting a uniform trichothecene chemotype population distinct from the dominant 3-ADON profiles reported in temperate production zones. The study provides a species-resolved mycotoxin risk assessment for South South Nigerian maize production. Keywords: Fusarium, ear rot, mycotoxin, fumonisin, South South Nigeria.