Leaf (or brown) rust caused by Puccinia triticina and yellow (or stripe) rust causcd by P. striiformis tritici are the two most important production constraints in several wheat growing regions of the world. Growing resistant cultivars has no cost to farmers and is the most environmentally friendly control measure. Resistance to rust diseases that is based on racc-specific genes is usually effective for about five years. An alternative approach to achieve resistance durability is to breed cultivars that have race-nonspecific type of resistance, Our studies show that durable resistance can be achicved by combining genes that confer slow rusting. Named slow rusting genes. viz. Lr34 and lr46 for leaf rust and Yr18 for yellow rust resistance. are associated with an increased latent period and reduced infection frequency and uredial size (or length of stripe in yellow rust). This indicates that the components of slow rusting are under pleiotropic genetic control: hence a single mechanism at the cellular level. formation of cell wall appositions. must be affecting all components, A single slow rusting gene confers only a small to moderate reduction in disease progress. but gene combinations result in additive effects with improved resistance, Between 3 to 4 genes for leaf rust and 4 to 5 for yellow rust must be combined to reduce disease progress to a level that only trace severity is seen at maturity under high disease pressure. Such resistance has been developed in CIMMYT wheats and is considered to be durable and race-nonspecific, Cultivars with slow rusting resistance must be released and promoted to permit long term rust control and enable breeders to emphasize breeding for higher yield potential and other desired traits. Diagnostic molecular markers for slow rusting genes are not yet available. so high priority must be given to obtaining them rather than identifying markers for race-specific genes.

Global Wheat Program

English

0111|R99-00PROCE|AL-Wheat Program|AL-ABC Program|3

Maria del Carmen Nava

INT0610

CIMMYT Staff Publications Collection