Submitted to: Phytopathology
Publication Type: Proceedings
Publication Acceptance Date: August 7, 2006
Publication Date: November 1, 2006
Citation: Engle, J.S., Marshall, D.S., Whitcher, L.C. 2006. Proposed major powdery mildew genes in eastern and southern wheat germplasm; in the past ten years. Phytopathology. Interpretive Summary: Powdery mildew of wheat is a world-wide pathogen that is economically limiting in areas such as the South Atlantic area of North America where it occurs annually. In years where the environmental conditions are conducive for disease development, powdery mildew can be yield limiting as far north as Michigan. One of the most cost effective and environmentally friendly ways to control powdery mildew is to incorporate resistance into wheat cultivars that are planted. There are two types of resistance: major gene which is controlled by different single genes and expressed predominately in the seedling stage, and minor gene which is controlled by several genes and expressed predominately as adult plants. To test lines that breeders are developing for powdery mildew resistance, two multi-state nurseries have been established, the Southern and Eastern Nurseries. In the lab, major gene resistance of the entries is measured on detached wheat seedling leaves for specific single genes. Results indicate that the major genes commonly observed were Pm3a, 3c, 3f, 5, and 8 with some occurrences of Pm1, 2, 4a, and 6. Not all major genes were screened in the lab, but the results indicate US breeders have consistently bred certain major genes into released cultivars over the past ten years.
Technical Abstract: Resistance to powdery mildew of wheat is controlled by major genes in adult and seedling stages or quantitative resistance in the adult stage. Entries in the PM nursery from Southern and Eastern US were screened on detached seedling leaves. The observed virulence patterns were then compared to virulence patterns of differential lines with known genes. There were some occurrences of Pm1, 2, 4a, and 6. The genes commonly proposed were Pm3c, 3f, 5, and 8. The Pm3a gene was commonly observed, but not in the 114 cultivars that were in multiple tests. These entries had inconsistent results within years and across years for cultivars that were replicated. Sources of variability in reactions may be a result of: variability in test protocol, changes in test isolates between years, non-pure seed source of the differentials, or entries of seed that came from non-pure sources. These results indicate test lines should be screened in multiple years for accurate projections of major PM genes in breeding entries. Results do not reflect all potential major PM genes present in US germplasm; genes such as Pm12, 16-17 and 25 were not included. Results indicate US breeders have consistently bred certain genes into released cultivars.