GENETICS OF THE YELLOW RUST RESISTANCE IN ADULT PLANTAS OF WHEAT CULTIVARS

Wheat (Triticum aestivum L.) yellow rusts caused by Puccinia striiformis f. sp. tritici is a disease that in the High Valleys of Mexico is growing in importance. This disease may cause up to 60 % of yield losses and diminish the industrial quality of the grain. 'Juchi F2000', 'Nahuatl F2000' and 'Tlaxcala F2000', are three varieties of bread wheat released in 2000 by the National Institute of Forestry, Husbandry and Agricultural Research for planting in rainfed areas. During their evaluation these varieties showed different responses tho the disease In order to determine the genetics of the resistance to yellow rust in these three varieties, they were crossed to the susceptible variety 'Avocet-YrA'. The parents and 148 F-3 families per cross were evaluated at Toluca, Mexico during the Summer 2002 under a natural incidence of yellow rust. The results of the F-3 families allowed to infer that the adult plant resistance in 'Juchi F2000' was conditioned by three minor genes of additive effects. In 'Nahuatl F2000' and 'Tlaxcala F2000' three to four genes of the same nature were identitied. A common gene in the three varieties was Yr18, which confers partial adult plant resistance to yellow rust. 'Nahuatl F2000' progeny showed higher levels of resistance, thus indicating that it has a higher number of resistance genes. The intercross of these three varieties may allow to increase the level of yellow rust resistance.