Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2005
Publication Date: May 1, 2006
Citation: Jackson, E.W., Avant, J.B., Overturf, K.E., Bonman, J.M. 2006. A quantitative assay of puccinia coronata f.sp. avenae dna in avena sativa.. Plant Disease. 90:629-636. DOI:10.1094/PD-90-0629 Interpretive Summary: Crown rust is caused by the fungus Puccinia coronata f.sp. avenae and is the most damaging disease of oat worldwide. To assess crown rust resistance, researchers rely on detailed measurements of symptoms and signs of disease on infected plants. These measurements can be tedious and may be biased by differences between individual raters. To overcome these problems our objective was to develop a molecular-based assay to specifically measure fungal growth associated with infected plants by quantifying the amount of fungal DNA present. Using five genotypes with varying levels of resistance, we compared results from the new assay with digital image analysis. We found that measuring fungal presence improved our ability to distinguish various levels of resistance among the genotypes and enabled us to identify resistant genotypes sooner after inoculation. we have developed a new way to measure rust disease resistance and have improved our ability to study the interaction between the crown rust pathogen and oat. Similarly assays should prove useful for other cereal rust diseases.
Technical Abstract: Crown rust, caused by Puccinia coronata f.sp. avenae, is the most damaging disease of oat. Quantification of the disease can be done by visual or digital assessments of diseased leaf area, lesion number, lesion size, and latent period. Laborious measurements of sporulation can also be made. As an alternative to these methods, a new quantitative assay was developed. The method employs simple inoculum application, quantitative sampling from inoculated areas, DNA extraction restricting loss of tissue, and real-time PCR using a pathogen-specific Taq Man® primers/probe set. Image analyses of genotypes with varying levels of crown rust resistance were compared to fungal DNA (FDNA) measured by the new assay. The moderately resistant genotype IA98822-2 was distinguished from susceptible genotypes at the seedling stage and the moderately resistant genotype O x T 107 was distinguished from the resistant cultivar TAM-O-301 at both leaf stages using FDNA. These separations were not evident with digital image analysis. The assay also detected fungal development earlier and more rapidly in genotypes with lower levels of resistance. The new assay can accurately quantify disease and should be useful for studying many aspects of the crown rust host-pathogen interaction where precise assessment of pathogen development is needed.