Progress in stacking aflatoxin and fumonisin contamination resistance genes in maize hybrids

Abstract

Contamination of maize grain with mycotoxins including aflatoxin and fumonisin poses a threat to human health and livestock. The objectives of this study were to determine the current status of incidence of ear rot causing fungi, which are associated with mycotoxin contamination, in southern African maize hybrids, and to check whether or not mycotoxin resistance genes can be stacked in a single product. The 327 hybrids were evaluated under natural conditions in replicated trials over two seasons at Cedara Research Station, which is hot spot site for ear rot diseases. Concurrently, aflatoxin and fumonisin resistant tropical maize inbred lines were crossed with South African adapted inbred lines. The resultant 72 single crosses were evaluated for fumonisin contamination, while 44 three-way crosses and their progenies (146 S2:3 families) were evaluated for both aflatoxin and fumonisin contamination under artificial inoculation. The Fusarium verticillioides was the most prevalent ear rot causing fungus, followed by Stenocarpella maydis, F. graminearum and Aspergillus flavus. The late maturing hybrids were more susceptible to ear rots contamination than their earlier counterparts. Stacking of mycotoxin contamination resistance genes was successful because five experimental single cross hybrids consistently accumulated low fumonisin levels (<4 ppm), both in the greenhouse and field trials. Three 3-way crosses displayed low contamination levels for both aflatoxins (<5 ppb) and fumonisins. Four S2:3 families accumulated low levels of both aflatoxins and fumonisins below the legal limits of 5 ppb and 4 ppm, respectively. Therefore significant progress can be realised in breeding mycotoxin resistant maize hybrids.