Leaf (brown) rust it the most important disease of wheat due to its world wide disteibution. In Iran , the disease is important on wheat, second to yellow rust . In the present study , virulence structure of 12 leaf rust isolates, selected from several samples collected from different parts of Iran was studied using leaf rust mear- isogenic lines. The results showed that near isogenic lines carrying Lr9 and Lr19 were resistant to the lines possessing Lr16 and LrB were susceptible to all isolates. As virulence factor for Lr19 was not found in any of the isolates, this can be an effective gene for its corporation into the national wheat breeding program, but due to its lack of virulence , its identification of wheat cultivars is rather difficult . According to the fripuencies of virulence , genes lr29, lr24 and lr28 with frequencies of 8.33, and 25% respectively , can also be used as resistant sources of leaf rust in breeding programs in Iran. Virulence factors for lr24,lr28 and lr29 were found only in isolates from Hamadan, dezful and mahdasht respectively , Therefore these genes are suggested to be used in comnination with other effective resistance genes such as lr34, an adult –plant resistance gene, for breeding and development of resistant cultivars. In general , the results obtained from the present investigation indicated that gentical variation in the population of leaf rust in Iran is limited . This can be mainly attributed to the wide use of genetically uniformed wheat cultivars with CIMMYT arigin.
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