Distribution and interaction of Fusarium crown rot and common root rot pathogens of wheat in Montana and development of an integrated management program for Fusarium crown rot

Abstract

This thesis had three objectives: i) Determining distribution of FCR and common root rot (CRR) of wheat in Montana; ii) Determining population dynamics between F. pseudograminearum and Bipolaris sorokiniana at different wheat development stages, and iii) Development of an integrated disease management program for Fusarium crown rot (FCR) using biological and fungicide seed treatments, cultivar resistance, and induced systemic resistance (SAR). Surveys of 91 fields over two years using qPCR identified FCR in 57% and CRR in 93% of the fields surveyed. Bipolaris sorokiniana, F. culmorum and F. pseudograminearum were isolated from 15, 13 and 8% of tillers respectively. FCR distribution was highly clustered while CRR was uniformly distributed with soil type, elevation and growing degree days influencing distribution. Data from intensively sampled fields estimated yield losses caused by FCR and CRR at 3.2 to 34.9% with losses influenced by pathogen population. This study is the first time qPCR was used to survey the distribution of FCR and CRR and to study the interaction of the respective pathogens. The effect of F. pseudograminearum and B. sorokiniana inoculum applied singly or in combination at three rates showed high and low rates of F. pseudograminearum inoculum reduced Bipolaris populations, while B. sorokiniana inoculations did not affect Fusarium populations in stems. Populations of both pathogens increased from heading until harvest with Fusarium colonizing stems earlier than Bipolaris. Mixed inoculations increased incidence of infection and co-infection relative to that observed in production fields. Both fungi alone or combined reduced the seedling counts. Grain yield was inversely correlated with Fusarium populations. Difenoconazole-mefenoxam seed treatment reduced FCR severity between 29.3-50% and fungal and bacterial seed treatments were ineffective. The cv. Volt was identified as partially resistant and had the highest levels of chitinase and beta-1, 3-glucanase activity of cultivars evaluated. Induction of SAR by Bacillus mycoides isolate BmJ or acibenzolar Smethyl significantly reduced the severity of FCR compared to water controls. Integration of cultivar resistance plus fungicide seed treatment or SAR induction provided equal control in greenhouse and irrigated trials. In a dryland field trial, integration of all management tools reduced FCR more than individual tools.