ARS | Publication request: Current resistance sources and breeding strategies to mitigate Ug99 threat

Submitted to: Wheat Genetics International Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: May 22, 2008
Publication Date: N/A

Technical Abstract: Continued spread of race Ug99 (TTKSK) of Puccinia graminis from Eastern Africa to Yemen and Iran, and its evolution to overcome resistance genes Sr24 and Sr36 has further increased the genetic vulnerability of wheat crop in Africa, Middle East and Asia where about 90% of the area is sown to moderately susceptible or susceptible varieties. Seedling and field screening has identified wheat materials with both race-specific (R) and adult plant resistance (APR). Although several R-genes, mostly alien in origin, continue to confer adequate to moderate field resistance to Ug99 and its variants, the most promising R-genes for immediate use and present in improved spring wheat materials include: Sr25, Sr26, SrTmp and 3-4 possibly novel R-genes. Other effective R-genes either need to be transferred to high yielding wheats from unadapted genetic backgrounds or their alien chromosome segments need shortening. These R-genes must be deployed in combinations to enhance longevity. Identification of improved spring wheats such as ‘Pavon 76’, ‘Kiritati’ and ‘Kingbird’ and advanced breeding lines with adequate levels of APR based on the durable “Sr2-Complex” has increased the possibility of developing and deploying spring wheat materials with durable APR in areas where Ug99 poses the greatest threat. This deployment strategy is likely to ease selection pressure in Ug99 to evolve further; which may help enhancing the effectiveness of R-genes in other lesser risk areas. Shuttle breeding between Mexico and Kenya was initiated in 2007 to enhance the frequency of plants with APR in segregating populations. High yielding spring wheats with APR and R-genes are being tested in multi-site yield trials in various countries. The 1st year results indicated the possibility of identifying replacement varieties with superior performance.