Abstract
Virulence factors of the yellow rust, Puccinia striiformis, populations in bread wheat were studied in Ecuador between 1973 and 2004. The number of virulence factors has increased markedly from very few in the early seventies to 16 at the end of the 90s. Isolates belonging to race 0E0 seem to be the ancestor of a rapid virulence evolution of yellow rust in Ecuador. This evolution can be explained by a single step mutation pattern. Virulence to the resistance genes Yr1, Yr2, Yr2+, Yr3V, Yr3ND, Yr4+, Yr6, Yr6+, Yr7, Yr7+, Yr9, Yr9+, Yr11, Yr12, Yr18, Yr24, Yr26 and those in the cultivars Carstens V (YrCV) Strubes Dickkopf (YrSD), Suwon92/Omar (YrSU), Spaldings Prolific (YrSP), Anza (YrA+) and Selkirk (YrSK). was identified. Virulence to Yr5, Yr8, Yr10, and Yr15 was not found. Postulation of resistance genes at the seedling stage of 14 Ecuadorian wheat cultivars indicated that these cultivars carry alone or in combinations the resistance factors Yr1, Yr2, Yr3, Yr6, Yr9 and/or other undesignated resistance factors. Yellow rust evolution in Ecuador has been associated with deployment of these resistance genes. None of these deployed Yr resistance genes are effective to the present yellow rust population in Ecuador.
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