Genetic diversity and trichothecene chemotypes of the Fusarium graminearum clade isolated from maize in Nepal and identification of a putative new lineage.

On smallholder farms in the foothills of the Himalayan Mountains in Nepal, fungi of the Fusarium graminearum clade cause Gibberella ear rot of maize and contamination with the 8-ketotrichothecenes nivalenol and deoxynivalenol. Previous DNA marker analyses of the F. graminearum clade from maize in Nepal found a high level of genetic diversity but were limited in detail or scope. The present study incorporated a collection of 251 field strains from a wide geographic distribution in Nepal and utilized sequencing of the MAT1-1-3 gene of the mating type locus to determine the number and frequency of lineages and species of the F. graminearum clade. The frequency of nivalenol and deoxynivalenol chemotypes was determined by chemical analysis and by TRI13 deletion-marker analysis. We found that Gibberella ear rot of maize in Nepal is associated with a complex of species of the F. graminearum clade - mainly Fusarium asiaticum and Fusarium meridionale, but also Fusarium boothii and a putative new lineage, which we have designated the 'Nepal lineage'. Fusarium graminearum sensu stricto, which dominates in maize elsewhere in Asia and worldwide, was not detected in Nepal. Although nivalenol production has been associated experimentally with lower virulence in maize ear rot and wheat head blight, this collection of the F. graminearum clade from maize in Nepal is dominated (4:1) by nivalenol producers, suggesting that traits other than crop plant pathogenesis affect population structure in this complex agroecosystem.