Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2007
Publication Date: 8/17/2007
Citation: Jackson, E.W., Obert, D.E., Menz, M., Hu, G., Avant, J.B., Chong, J., Bonman, J.M. 2007. Characterization and mapping oat crown rust resistance using three assessment methods. Phytopathology.p.1063-1070 Interpretive Summary: Interpretative Summary: Identifying genetic mechanisms in oat responsible for resistance to crown rust requires; i) generating a population of lines that segregate for resistance by crossing a resistant parent with a susceptible parent, ii) extensive work identifying and mapping molecular markers on the population, iii) accurately scoring the severity of crown rust disease on plants of each line and both parents, and iv) evaluating the relationship between disease resistance and the molecular markers using sophisticated statistical computer software. One of the most difficult requirements in this process is accurate disease assessment. In this study we used a new disease assessment assay developed at the USDA-ARS National Small Grains and Potato Research Unit in Aberdeen, ID to generate disease resistance data from a segregating mapping population. The new assay, which estimates the amount of fungal tissue present in infected oat leaves, was compared to visual ratings and digital image analysis of disease. Using the new assay we were able to more accurately map resistance and detected additional plant genes responsible for reducing disease. Our work has shown the importance of using precise methods of disease evaluation and will lead to the development of new cultivars with improved crown rust resistance.
Technical Abstract: Technical abstract: Resistance is the primary means of control for crown rust of oat (Avena sativa L.), caused by Puccinia coronata f. sp. avenae, and better knowledge of the genetics of resistance will enhance resistance breeding. Disease data were generated in the field and greenhouse for parents and recombinant inbred lines of the Ogle/TAM O-301 (OT) oat mapping population using; i) a new quantitative assay that employs quantitative real-time polymerase chain reaction (q-PCR) to estimate fungal growth in the host, ii) digital image analysis, and iii) visual ratings. Data from each assessment method were evaluated for the ability to map a major gene from the cultivar Ogle and potential quantitative trait loci (QTL) contributed by Ogle and TAM O-301. All three assessment methods identified the major gene in Ogle, which was mapped to linkage group OT6. The resolution produced by q-PCR, however, enabled more precise mapping of the major gene. Furthermore, data generated by q-PCR permitted identification of QTL on linkage groups OT32 and OT2 conferred by TAM O-301, one of which (OT2) was indiscernible using data from the visual and digital assessments. The new method of precisely phenotyping crown rust resistance provided a more accurate and thorough means of dissecting resistance in the OT mapping population. Similar methods could be developed and applied to other important cereal rust diseases.