QTL associated with powdery mildew resistance in Avena sativa

The powdery mildew and rust fungi are highly successful pathogens that pose a constant threat to UK cereals where infection may drastically reduce grain quality and yield. The fungi are biotrophic, feeding on living plant cells, depriving the plant of nutrients and causing premature leaf senescence. Genetic host resistance offers disease control that is potentially far more desirable than the application of fungicides. Chemical control is not only likely to become constrained by the loss or reduction of currently available products but is also perceived as a threat to the environment and consumer. At the same time, climate change effects are likely to increase both disease pressure and disease range. However, the rapid evolution of pathogen virulence has nullified many single genes for resistance.
Powdery mildew (Blumeria graminis f.sp. avenae) is a fungal disease which can reduce oat yield. This study used a population developed from a cross between two spring oats, Maldwyn (which shows adult plant resistance that limits both primary infection and subsequent colony growth) and Emotion to identify QTL for mildew resistance. An F2 population of 200 individuals was phenotyped in the glasshouse for mildew infection type and cover both prior to and on heading. Plants were inoculated with race 5 B. graminis f.sp. avenae, and an epidemic developed. Each plant was scored at the juvenile stage (5th leaf unrolling) and again as adults (flag leaf expanded) for percentage leaf area affected; for juveniles the sum of scores from leaves 3, 2, 1, and for adults the sum of scores from the flag leaf, flag-1 and flag-2, were summed as an overall indicator of disease. In addition infection type (IT) was recorded on the uppermost leaf at each stage using a 0-4 scale where: 0 = no visible symptoms; 1 = colonies just visible, no apparent sporulation; 2 = small colonies, sporulation questionable; 3 = moderate, obviously sporulating colonies; 4 = large, freely sporulating colonies. Note was taken if colonies were associated with necrosis. In addition, heading date and height on harvest was recorded. A genetic linkage map was produced using a combination of microsatellite and DArT markers. QTL for both height and heading date obtained show similarity with QTL for these traits obtained in other populations. Novel QTL associated with disease resistance were found.