Gibberella zeae: Population structure, mycotoxin profiles, real-time PCR quantification, and host resistance

Gibberella zeae, a causal agent of Fusarium head blight (FHB) of wheat and other small grains, also infects potato and sugar beet in the United States. Population structure and mycotoxin profiles of the fungus associated with noncereal crops or across wheat cultivars have not been studied extensively. Studies on G. zeae populations and host resistance are essential for effective management of FHB. To gain insight into the population structure and mycotoxin profiles of G. zeae isolates from cereal and noncereal in the upper midwestern United States, 336 single-spore isolates sampled from barley, wheat, potato and sugar beet were analyzed using variable number tandem repeat (VNTR) markers and trichothecene-specific markers. A subset of 32 representative isolates from the four crops was sequenced and confirmed to belong to clade 7 of G. zeae. High gene and genotype diversity, and low population differentiation due to high gene flow were observed in all populations and subpopulations. All isolates had deoxynivalenol (DON) markers with predominant 15-acetyl-deoxynivalenol (15-ADON) markers. The frequencies of isolates associated with 3-ADON and 15-ADON markers in wheat varied greatly among sampling sites but not with cultivar groups. To analyze relationships among disease severity, fungal biomass, and mycotoxin produced in planta, a subset of the 21 G. zeae isolates from wheat, potato, and sugar beet were further inoculated and evaluated on the FHB-susceptible wheat cultivar Grandin in the greenhouse. All isolates induced typical FHB symptoms in wheat and produced a wide range of trichothecenes and fungal biomass. FHB severity was positively correlated (P < 0.001) with fungal DNA content and DON production. In a separate study, 135 F9 recombinant inbred lines (RILs) were assessed for resistance to FHB and DON content in the greenhouse during 2006 and 2007. Forty-two resistant RILs were analyzed using seven known SSR markers linked to FHB resistance. Among the 42 RILs, 48% had markers linked to both type I and II resistance alleles, and 29% showed greater overall resistance to FHB and DON content than both resistant parents. Overall, these findings will be useful for assessing mycotoxin risks and formulating FHB management strategies in cereal and noncereal crops.