Submitted to: Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2010
Publication Date: 1/6/2011
Citation: Desjardins, A.E., Proctor, R. 2011. Genetic diversity and trichothecene chemotypes of the Fusarium graminearum clade isolated from maize in Nepal and identification of a putative new lineage. Fungal Biology. 115:38-48. Interpretive Summary: The results of this research indicate that the population of the fungus Fusarium graminearum in corn from smallholder farms in Nepal is highly diverse compared to the population in the US. Fusarium graminearum is one of the most frequent causes of corn ear rot worldwide and the predominant cause of wheat and barley head blight in North America, Europe, and some parts of Asia. The fungus can also contaminate grain crops with toxins known as trichothecenes. In recent years, genetic analyses have revealed that the worldwide population of F. graminearum exhibits considerable genetic diversity, and based on this the fungus has been subdivided into different lineages and even different species by some researchers. Lineage 7 predominates and typically is the only lineage recovered in most corn and wheat growing areas of the US. This contrasts the situation on corn from smallholder farms in Nepal, where lineage 2, 3, 6, and 10 occur and lineage 7 is apparently absent. These results provide information on the potential risks of different lineages of F. graminearum to US agriculture.
Technical Abstract: On smallholder farms in the foothills of the Himalayan Mountains in Nepal, Fusarium graminearum causes Gibberella ear rot of maize and contamination with the 8-ketotrichothecenes nivalenol and deoxynivalenol. Previous DNA marker analyses of F. graminearum populations 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 F. graminearum lineages. 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 lineages of the F. graminearum clade-mainly lineages 2 and 6, but also lineage 3 and a putative new lineage, which we have designated lineage 10. Lineage 7, 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, the F. graminearum population 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.