Fusarium ear blight of wheat: the use of quantitative PCR and visual disease assessment in studies of disease control

Abstract

Quantitative PCR analysis and visual disease assessment (VDA) were used to study Fusarium culmorum and F. poae ear blight of wheat and its fungicidal control in three glasshouse trials (1994–5 and 1996–7). VDA indicated high levels of both diseases in the trials, while PCR analysis showed that the amounts of F. poae detected in infected plants were low relative to the amounts detected for F. culmorum. PCR and VDA analysis both indicated that the demethylase‐inhibiting (DMI) fungicides prochloraz and tebuconazole significantly decreased F. culmorum and F. poae ear blight. The PCR results, however, revealed levels of disease control by fungicide treatments that were consistently higher than those suggested by VDA. Overall, both fungicides appeared equally effective in controlling the two pathogens. PCR and VDA analysis indicated that the anilino‐pyrimidine fungicide pyrimethanil had no significant effect on F. culmorum ear blight. Correlations between VDA at cereal growth stage 80 and PCR analysis were similar for F. culmorum and F. poae. Yield analysis, as measured by 1000 grain weight, indicated that DNA content more accurately predicted yield loss than did VDA scores. Inoculation with F. culmorum significantly reduced yield and significant relationships were observed between F. culmorum disease (as assessed visually or by PCR) and yield, with yield decreasing as disease increased. In contrast, inoculation with F. poae had no significant effect on yield and no significant relationships were observed between F. poae disease and yield. These results have important implications for field studies of Fusarium ear blight of wheat because they highlight the importance of identification of the causal organisms to the species level.