Abstract only

Globally, wheat is the most important food crop, the most traded food crop and is the main source of caloric intake for over 2.5 billion poor people. Major constraints to wheat production can affect global food security. The major biotic constraint to wheat production is the disease of stripe rust, caused by Puccinia striiformis. Since the beginning of this century, changes in virulence and aggressiveness of this pathogen have seen severe epidemics of new pathotypes sweep the globe. Breeding resistant varieties is the best method to control this disease. This is most easily done through the incorporation of seedling (all-stage) resistance genes that usually confer immunity. However this resistance places a strong selection pressure on the fungus to evolve, with specific genes often lasting only a few years before breaking down, leaving the crop susceptible. Quantitative resistance genes can provide near-immunity to the disease if 4-5 loci are combined in the same genetic background. Many of these types of genes are considered durable and have been effectively used for up to 80 years. The first publications relating to quantitative trait loci to stripe rust in wheat appeared in 2000. Since then there have been 34 publications that have identified over 140 QTLs. By taking the flanking markers to each of these QTLs, and placing them on consensus maps, a picture of the current known diversity of these types of genes is revealed. There are at least 49 regions on the wheat genome that are known to contribute to disease resistance. Some of the more commonly identified regions have pleiotropic effects, exemplified through the cloning of the Lr34/ Yr18/Sr57/Pm38/Ltn1 gene. This gene confers partial resistance to multiple iseases including leaf, stripe and stem rust, powdery mildew and also confers the phenotypic marker of leaf tip necrosis. Other likely pleiotropic loci that have been identified in multiple QTL analyses include the Lr46/Yr29/Pm39/Ltn2 locus on chromosome 1BL, Lr67/Yr46/Sr55/Pm46/Ltn3 on 4D and the Sr2/Yr30/Lr27/Pbc1 locus on 3BS. As these loci are generally only observed to be effective in the adult plant stage, they have been termed Pleiotropic Adult Plant (PAP) resistances. Another class of quantitative resistances are the High Temperature Adult Plant (HTAP) resistances that are ineffective in seedlings and in plants grown under lower temperatures, but usually confer quite high levels of resistance in adult plants grown under high temperatures. Two HTAP loci have been given gene designations, Yr36 on 6BS and Yr39 on 7BL with the former being cloned. Other HTAP loci have been identified on 1BL, 2BS, 2DS, 3BL, 5B and 6AS. Finally there are numerous other genomic regions that confer low levels of partial resistance to stripe rust. Often these are not significant in all environments tested, but can work in an additive fashion when combined with each other and the above mentioned PAP and HTAP loci to confer durable resistance. This paper will outline the most important genomic regions that will benefit from future research.

Global Wheat Program

English

Lucia Segura

INT3219|INT0610|INT2833|INT3206|INT2411

CIMMYT Staff Publications Collection