Wheat rust in Asia: meeting the challenges with old and new technologies

Author(s): Singh RP, William HM, Huerta-Espino J, Rosewarne G

Abstract

The rust diseases of wheat pose a constant threat to sustainable wheat production and thus food security in Asia. If susceptible wheat cultivars are grown, approximately 60 and 40 million hectares could experience periodic epidemics of leaf rust and stripe rust, respectively. Avoiding major rust epidemics in the region is a complex challenge, given that fewer cultivars are being cultivated over large areas, that several of those cultivars are protected by the same resistance genes, and that there is free movement of new virulent races in most of west and south Asia. Monitoring the evolution and movement of new rust races and diversifying cultivars sown in the region based on genetic information could help reduce losses, provided newly susceptible cultivars are withdrawn quickly. Using race-specific resistance genes in combinations could enhance their longevity. Linked DNA markers show promise for achieving such combinations; however, a national and regional deployment strategy is necessary to achieve long-term success. The most promising long-term control strategy is to breed and deploy cultivars carrying durable resistance based on minor, slow rusting genes with additive effects. CIMMYT studies show that combining 4-5 such genes results in a high level of resistance, comparable to immunity. Traditional genetic and molecular mapping studies have demonstrated high genetic diversity for such minor genes, but significant investment is necessary to identify closely linked markers that could be used effectively in marker-assisted selection. Targeted incorporation of durable resistance genes into mega-cultivars grown in Asia by using a ‘single-backcross selected-bulk breeding scheme’ is being pursued at CIMMYT with encouraging results.

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