Characterization of mating type, spore killing, and pathogenicity of Fusarium verticillioides populations from maize in China

Abstract

Sexual reproduction in fungi promotes genetic diversity and helps the fungus to adapt to environmental stresses. Fusarium verticillioides is a heterothallic filamentous ascomycete that is a major cause of maize ear and stalk rot worldwide, while also posing a threat to human and animal health by producing various mycotoxins. Sexual reproduction in F. verticillioides is controlled by the MAT-1 and MAT-2 loci, which mandate that only strains of opposite mating types can mate to yield perithecia and ascospores. Nevertheless, there exists a phenomenon called ‘spore killing’, in which only four typical ascospores appear in the asci following a cross between a strain carrying the spore killer allele (SkK) and one with the spore killer sensitive allele (SkS). In this study, 31 isolates of F. verticillioides collected from eight provinces in China during the maize growing season from 2014 to 2020 were compared based on their mating type, spore killing genotype, and pathogenicity. To determine the mating types and spore killing genotypes of these isolates, partial sequences were amplified from the MAT loci and the SKC1 gene, respectively. The PCR results showed that out of the 31 isolates, 18 were MAT-1 and 13 were MAT-2, and that 25 had SkK genotypes and 6 had SkS genotypes. Genetic crosses between LNF15-11 (MAT-2) and 18 MAT-1 isolates produced normal perithecia with varying numbers. However, crosses between LNF15-11 and the 3 isolates (SDF18-36, HNF14-8, and GSF19-6) produced only four ascospores per ascus, while the remaining isolates except SDF18-28, yielded eight ascospores per ascus. These findings suggest that the SKC1 amplicon variation can be used to differentiate SkK and SkS genotypes in the field and that the 3 isolates are truly SkS genotypes with the MAT-1 allele. Altogether, this study contributes to our knowledge of the mating type and spore killing genotype of F. verticillioides in China and offers valuable strain resources for investigating heterothallic sexual reproduction.