Fusarium head blight (FHB) or scab, caused by Fusarium graminearum Schwabe [sexual stage Gibberella zeae (Schwein.) Petch], is a destructive disease of small grain cereals. Fusarium graminearum produces the mycotoxin deoxynivalenol (DON), which accumulates in and lowers the value and quality of grain. Field experiments were conducted from 2007 to 2009 to determine if two winter wheat cultivars varying in FHB phenotype response differentially accumulated DON. Secondary objectives were to model the relationship between FHB severity and DON, determine if environment (= year) influenced DON accumulation in the two cultivars, and measure the percentage of Fusarium-damaged kernels (FDK) in the two cultivars. The cultivar 'Harry' with a moderately resistant FHB phenotype consistently accumulated more DON (P <= 0.0358) than '2137' with a susceptible phenotype. The relationship between FHB severity and DON was linear and positive for both cultivars in all three years (0.32 <= R-2 <= 0.60; 0.0053 <= P <= 0.1092). Environment (= year) had a significant effect (P < 0.0001) on DON accumulation in both cultivars, and this effect was attributed to differences in rainfall amount and duration in the months of May and June. DON accumulation was highest in 2008 (average of 33.2 ppm in 'Harry' and 21.2 ppm in '2137') when there was steady, above-average rainfall in May and June. FDK was highest in 2008 and was higher in 'Harry' (64%) than in '2137' (46%). The results from this study suggest that a winter wheat cultivar with a moderately resistant FHB phenotype can be susceptible to FDK and DON accumulation. Based on these results, there is a need to standardize the criteria (FHB intensity, FDK, DON) for characterizing wheat cultivars as resistant or susceptible to FHB.
To improve the efficiency of gene disruption in Stagonospora nodorum, the putative KU70 gene encoding the Ku70 protein involved in the nonhomologous end-joining double DNA break repair pathway was identified and deleted. The KU70 disruption strain showed no apparent defect in vegetable growth, conidiation and pathogenicity on wheat and barley compared with the wild-type strain. The effect of the absence of KU70 on gene replacement frequency was tested by disruption of TOXA encoding toxin A and LIP2 encoding a putative lipase. Frequency of gene replacement for both genes was dramatically increased in the KU70 disruption strain, compared with the low frequency in the wild-type recipient.
