Diversity of virulence phenotypes among annual populations of wheat leaf rust in Israel from 1993 to 2008

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat-producing areas worldwide. The Israeli population of wheat leaf rust has been consistently monitored since 1993. A total of 840 single urediniospore isolates from Triticum aestivum (567), T.dicoccoides (119) and T.durum (154) were analysed during 1993-2008. The structure of the pathogen population has changed to a large extent since 1993. The annual populations of P.triticina were separated into two distinct groups: 1993-1999 and 2000-2008. Differentiation among the annual pathogen populations, as well as between the overall populations of the 1990s and 2000s, could be mainly attributed to the following forces: (i) migration of leaf rust urediniospores from neighbouring regions; and (ii) selection pressure of new yellow rust-resistant wheat cultivars that have been introduced into Israel since 1997. Genetic multiplicity of wild emmer contributes to P.triticina variability in Israel. Leaf rust populations collected from common wheat, wild emmer and durum wheat differed. The population that originated from T.durum was rather stable during the years of the survey, whereas that from T.aestivum changed significantly from the 1990s to the 2000s. Diversity within the annual populations of P.triticina was highest in 1994 when many new pathotypes and associations between virulences were observed. Single-step derivatives of the new pathotypes became dominant after 2000. Significant changes in virulence frequency to a number of Lr genes (e.g. Lr2a, Lr15, Lr17, Lr21, Lr26) were also registered in 2000-2008.