ABSTRACT
Distribution of Fusarium crown rot (FCR) and common root rot (CRR) pathogens associated with wheat (Triticum aestivum) in 91 fields in Montana were determined during the 2008 and 2009 crop seasons using real-time quantitative polymerase chain reaction (qPCR) and conventional isolation methods. Correlations (P < 0.001) were found between detection methods for both diseases. FCR was detected in 57% of the fields and CRR was detected in 93% of the fields surveyed. Percent incidence based on isolation from individual tillers was Bipolaris sorokiniana (15%), F. culmorum (13%), and F. pseudograminearum (8%). FCR populations were highly variable across the regions and were not detected in any fields from the Gb5 soil types of Judith Basin and Fergus counties. The spatial distributions of FCR and CRR were affected by elevation, soil type, and temperature. High FCR populations were associated with spring wheat crops rather than winter wheat based on qPCR (P < 0.001). FCR and CRR could produce yield losses in a range of 3 to 35%. This study is the first time that qPCR was used to survey these two pathogen groups, and the merits and weakness of qPCR relative to traditional isolation methods are discussed.
ABSTRACT
Fusarium pseudograminearum and Bipolaris sorokiniana are causal agents of Fusarium crown rot and common root rot, respectively, of wheat and cause significant losses worldwide. Understanding the population dynamics between these two pathogens at late stages of wheat development is needed. The effect of F. pseudograminearum and B. sorokiniana inocula applied singly or in mixtures at seeding to spring wheat 'Hank' was measured using seedling stand, grain yield, and pathogen populations in the first internode at heading, milk, and harvest stage of wheat development using real-time quantitative polymerase chain reaction. High and low rates of F. pseudograminearum inoculum reduced B. sorokiniana populations in field trials but B. sorokiniana inoculations did not affect F. pseudograminearum populations. Populations of both pathogens increased from heading until harvest, with F. pseudograminearum colonizing lower internodes earlier than B. sorokiniana. Neither pathogen prevented infection by the other in the first internode of wheat stems. Inoculations increased incidence of infection and co-infection relative to natural settings observed for both pathogens. At the seedling stage, both fungi, individually or combined, reduced the seedling stands when compared with a noninoculated control for the three location-years. Grain yield and F. pseudograminearum populations were inversely correlated, while B. sorokiniana populations were not correlated with yield.
