Are rust pathogens under control in the Southern Cone of South America?
Approximately nine million ha of wheat (Triticum aestivum and T. durum) were sown annually in the Southern Cone of South America (Argentina, Brazil, Chile, Paraguay and Uruguay) during 2003-2007. Presently, leaf rust (caused by Puccinia triticina) is the most important rust of wheat throughout the region. The pathogen population is extremely dynamic leading to short-lived resistance in commercial cultivars. Leaf rust management relies on the use of resistant cultivars and fungicides. Sources of adult plant resistance conferred by minor additive genes have been increasingly used in breeding programs to obtain cultivars with more durable resistance. Stripe rust (P. striiformis f. sp. tritici) is endemic in central and southern Chile, where fungicides are required to control the disease on susceptible cultivars. Stem rust (P. graminis f. sp. tritici) has not caused widespread epidemics in the last 25 years due to the use of resistant cultivars. Virulence to Sr24 and Sr31, the most important genes conferring resistance to local races, has not been reported in the region. The areas sown with cultivars susceptible to local races in Argentina and Uruguay have increased in recent years. Since most varieties sown in the region are susceptible to Ug99 or derived races, testing and selection for resistance in Kenya, facilitated by the Borlaug Global Rust Initiative, is highly relevant for research aimed at preventing epidemics, which may occur if these races migrate, or are accidentally introduced to our region. The resistances identified in east Africa will also contribute to increasing the levels of resistance to current local races.