Seasonal variation in mycoflora associated with asymptomatic maize grain from smallholder farms in two provinces of South Africa

Abstract

Seed quality plays an important role in the establishment of healthy crop stands. The aim of this study was to identify the mycoflora associated with maize grain collected over two growing seasons, one experiencing severe drought, from smallholder farms in KwaZulu-Natal (KZN) and the Eastern Cape (EC). These are two adjacent provinces in South Africa with many maize-producing smallholder farmers. Asymptomatic maize ears were collected at harvest during the 2014/2015 and 2015/2016 maize growing seasons from farms located in Hlanganani (KZN), Ntabamhlophe (KZN), KwaNxamalala (KZN), Bizana (EC) and Tabankulu (EC). Maize grain was subjected to seed health tests using the agar plate method. The percentage incidence of fungal species isolated from maize grain was determined with species identities confirmed by ITS sequencing. Eleven fungal genera were identified with Fusarium species and Stenocarpella maydis the most prevalent. Fusarium verticillioides, Fusarium graminearum and S. maydis were isolated from all sites in both seasons. No fungal species exhibited a higher incidence in the drought season across all sites. F. graminearum and S. maydis had higher incidences in the wetter season at four and three sites, respectively. F. verticillioides had a greater incidence at the EC sites, particularly the coastal Bizana site. We conclude that local factors that a ect the inoculum levels of each species, such as land preparation, previous crop, amount of debris from previous season, fertilizer application, and the micro-environment at field scale had a greater impact than the drought season on the population structure of ear-rot pathogens. The widespread presence of fungi that are potentially mycotoxin-producing in asymptomatic maize grain poses health risks to consumers and is worthy of further investigation.