Gibberella Ear Rot of Maize (Zea mays) in Nepal: Distribution of the Mycotoxins Nivalenol and Deoxynivalenol in Naturally and Experimentally Infected Maize

Abstract

The fungus Fusarium graminearum (sexual stage Gibberella zeae) causes ear rot of maize (Zea mays) and contamination with the 8-ketotrichothecenes nivalenol (1) or 4-deoxynivalenol (2), depending on diversity of the fungal population for the 4-oxygenase gene (TRI13). To determine the importance of 1 and 2 in maize ear rot, a survey of naturally contaminated maize in Nepal was combined with experiments in the field and in a plant growth room. In the survey, 1 contamination was 4-fold more frequent than 2 contamination and 1-producers (TRI13) were isolated more than twice as frequently as 2-producers (Psi TRI13). In maize ear rot experiments, genetically diverse 1-producers and 2-producers caused ear rot and trichothecene contamination. Among strains with the same genetic background, however, 1-producers caused less ear rot and trichothecene contamination than did 2-producers. The high frequency of 1 contamination and the high virulence of many 1-producers are of concern because maize is a staple food of rural populations in Nepal and because 1 has proven to be more toxic than 2 to animals.

Population Structure of and Mycotoxin Production by Fusarium graminearum from Maize in South Korea

“…Trichothecene production need not be correlated with phylogenetic lineage (41). In the populations we sampled, all of the lineage 3 and lineage 7 isolates produced deoxynivalenol, and all lineage 2 isolates and all but one lineage 6 isolate produced nivalenol ( (28), with DON-producing strains being perceived as more virulent than NIVproducing strains (8). Trichothecene production is not thought to be important in aggressiveness toward rice.…”

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

“…In a recent survey of maize seed samples in Nepal, in contrast, nivalenol contamination was four-fold more frequent than deoxynivalenol contamination, and nivalenol producers (TRI13) of the F. graminearum clade were isolated more than twice as frequently as deoxynivalenol producers (jTRI13) (Desjardins et al 2008). The high frequency of nivalenol contamination is of special concern because nivalenol has proven to be more toxic than deoxynivalenol in most animal systems (Desjardins 2006). In addition, the high frequency of nivalenol producers of the F. graminearum clade suggested that deoxynivalenol-producing F. graminearum sensu stricto, which appears to be dominant on maize elsewhere, might be less common on maize in Nepal.…”

“…Fungi of the Fusarium graminearum clade (teleomorphs Gibberella species) infect wheat, barley, maize, and other cereal crops worldwide and contaminate grain with trichothecene mycotoxins that are harmful to human health (Desjardins 2006;Leslie & Summerell 2006). On smallholder farms in the foothills of the Himalayan Mountains of Nepal, the F. graminearum clade causes Gibberella ear rot of maize and contamination with the 8-ketotrichothecenes nivalenol and deoxynivalenol (Desjardins et al 2008).…”

“…On smallholder farms in the foothills of the Himalayan Mountains of Nepal, the F. graminearum clade causes Gibberella ear rot of maize and contamination with the 8-ketotrichothecenes nivalenol and deoxynivalenol (Desjardins et al 2008). The high frequency of trichothecene contamination is of concern because maize is a staple food of rural populations in Nepal (Paudyal et al 2001).…”

“…Consequently, in the United States, Europe, and Korea, where F. graminearum sensu stricto dominates, maize seed consistently is contaminated with deoxynivalenol rather than nivalenol (Tanaka et al 1988;Ryu et al 1996;Castillo et al 2008). In a recent survey of maize seed samples in Nepal, in contrast, nivalenol contamination was four-fold more frequent than deoxynivalenol contamination, and nivalenol producers (TRI13) of the F. graminearum clade were isolated more than twice as frequently as deoxynivalenol producers (jTRI13) (Desjardins et al 2008). The high frequency of nivalenol contamination is of special concern because nivalenol has proven to be more toxic than deoxynivalenol in most animal systems (Desjardins 2006).…”