Distribution and Nucleotide Diversity of in Wild Emmer Populations and Chinese Wheat Germplasm.

Stripe rust, caused by f. sp. (), is a devastating fungal disease of wheat. The wild emmer gene, (), which confers a strong broad-spectrum resistance to isolates, is composed of kinase and pseudokinase domains. The analysis of 361 wild emmer accessions from a wide range of natural habitats confirms that functional is distributed mainly along a narrow axis from Mt. Carmel to Mt. Hermon regions, in the northern part of Israel, where environmental conditions are favorable to the onset of stripe rust. An analysis of full-length DNA sequences from 49 wild emmer accessions identified three haplotypes and extremely low nucleotide diversity (π = 0.00002). The sequence diversity of is 9.5 times lower than that of broad-spectrum partial resistance gene (π = 0.00019), and both are in sharp contrast to the high level of nucleotide diversity previously reported for race-specific resistance genes (e.g., and ). However, the nonfunctional sequences possess high level of nucleotide diversity (π = 0.07). These results may reflect the different resistance mechanisms and the different evolutionary processes that shaped these resistance genes. was absent in 189 Chinese wheat landraces and was present in only 1.02% of the 583 tested modern Chinese wheat cultivars. These results corroborate our previous results showing that was absent in 94% of a worldwide collection of 513 wheat cultivars, therefore indicating the importance of in wheat stripe rust resistance breeding programs in China and elsewhere around the globe.