New genes for leaf rust resistance in CIMMYT durum wheats

Leaf rust, caused by Puccinia triticina, has become an important disease of durum wheat (Triticum turgidum) in Mexico since the detection in 2001 of BBG/BN, a new race virulent on all common cultivars and on more than 80% of CIMMYT's durum wheat collection. We investigated the genetic basis and diversity of resistance in nine durum genotypes that are highly resistant to the new race. These resistant durums were crossed with the susceptible cv. Atil C2000 and intercrossed in a half diallel arrangement. Five diverse sources of resistance were identified by evaluating parents, F-1, F-2, and F-3 populations in greenhouse and/or field trials under artificial epidemics of race BBG/BN. The same pair of partially dominant complementary genes determined resistance in Jupare C2001, Hualita, and Pohowera. Somateria and Llareta INIA shared the same dominant resistance gene, whereas a partially dominant gene conferred resistance in two sister lines, Guayacan 2 and Guayacan INIA. A different partially dominant gene present in Storlom was linked in repulsion to another partially dominant gene in Camayo. These diverse resistance genes can be used effectively to control leaf rust, preferably by deploying them in combinations.