Deoxynivalenol levels and chemotype frequency in barley cultivars inoculated with two chemotypes of Fusarium graminearum

Corn kernels colonized by Fusarium graminearum were spread between lines of barley (Hordeum vulgare) in an irrigated Fusarium head blight (FHB) nursery at a 2: 1 ratio of isolates producing 15-acetyldeoxynivalenol (15 ADON) to isolates producing 3-acetyldeoxynivalenol (3 ADON) (in 2008) or 1: 1 ratio (in 2009, 2010). In 2008, it was the first use in this field of a 3 ADON isolate after 9 years of artificial inoculation with exclusively 15 ADON isolates. Sets of three 2-row and three 6-row cultivars were used as checks throughout the nursery, representing a range of susceptibility to FHB. Composites of these cultivars were prepared and analysed for per cent F. graminearum infection, chemotype frequency and levels of deoxynivalenol (DON), 3 ADON and 15 ADON. Seed infection by F. graminearum ranged from 83.5% (2009) to 98.5% (2010), with little difference across the nursery. In 2008, the chemotype distribution of F. graminearum and DON levels on infected kernels showed a several-fold difference from the eastern side (67% 3 ADON isolates and 46 ppm DON) to the western end of the field (16% 3 ADON isolates and 13 ppm DON), but not in the subsequent 2 years. In both 2009 and 2010, the 3 ADON chemotype was recovered from only 18% and 13% of the seeds, and overall average DON levels were 18 ppm and 24 ppm, respectively. In 2008, the highest DON and 3 ADON levels were associated with the highest frequency of the 3 ADON chemotype. In all years, the recovery of isolates did not reflect the ratio of the initial inoculum, suggesting that other factors influenced the ultimate infection of the seed. However, the relative relationship among the barley cultivars was consistent throughout all 3 years: DON levels were much lower in the most resistant cultivars compared with the most susceptible cultivars in all years and composites. Genotypic response to DON accumulation did not show strong interaction with 3 ADON frequency, suggesting that the underlying genetic resistance of the barley cultivars is cross-applicable between chemotypes. © 2013 The Canadian Phytopathological Society.