Journal Paper

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Journal: نهال و بذر
Year:1387 | Volume:24 | Issue:1
Start Page:207 | End Page:213



Persian Version






Information Journal Paper




 Start Page 207 | End Page 213


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 Stem or black rust of wheat, caused by Puccinia graminis Pers. f. sp. tritici Eriks. and Henn (Pgt), was the most feared and devastating disease of wheat  at one time worldwide. The fear from stem rust was understandable because an apparently healthy looking crop about 3 weeks prior to harvest could reduce to a black tangle of broken stems and shriveled grain by harvest. The disease has been controlled by deploying resistance genes in commercial cultivars. Successful control of disease over forty years has significantly reduced the risk of crop losses and research activities as well. Almost 50 stem rust resistance (Sr) genes are now catalogued, several of which have been used in commercial wheat cultivars worldwide. With the exception of Sr2 that confers slow rusting race non-specific resistance at adult-plant stage, all other Sr- genes are race specific, and are expressed at both seedling and adult-plant stages. Resistance gene Sr2 in addition to other unknown minor genes known as 'Sr2-complex' provided the foundation for durable resistance to stem rust in germplasms developed in CIMMYT. In addition to Sr2 some other stem rust resistance genes derived from alien resistance genes sources such as Sr24, Sr26, and Sr31 and more recently Sr38 have been used widely. Deployment of stem rust resistance genes declined the importance of stem rust worldwide. All translocations except with Sr26, are also carrying additional resistance genes for other wheat diseases. Sr31 known to be located on 1B.1R translocation is completely linked with Yr9 and Lr26, genes conferring resistance to stripe and leaf rust. The 1B.1R translocation has been used widely in spring, facultative and winter wheat breeding programs in Europe, China, Russia, and USA and in several cultivars in developing countries derived from CIMMYT germplasms during mid 1980s. It was not until 1999 that the first virulent pathotype to Sr31 was detected in Uganda. This race is commonly known as Ug99 and also has been designated as TTKSK using North American nomenclature system. Following its first detection in Uganda, investigation in neighboring countries revealed that same race migrated to Kenya in 1999/2002, to Ethiopia in 2003, and finally it was reported in Yemen in 2006. The migration route of Ug99 matches with the migration route of Yr9 virulent race of Puccinia striiformis f. sp. tritici (Pst) during 1986/1991. The Yr9-viruelnt Pst pathotype migrated from Africa to Iran in 1992 and caused 1 and 1.5 million tones crop losses in 1992 and 1993 respectively. The pattern of airflows and wheat growing distribution in these areas supports the migration routes similar to that taken by Yr9-virulent Pst pathotype in 1990s. Similar genetic background of wheat cultivars growing in the possible migration route of Ug99 that are highly susceptible to this pathotype will also enhanced the potential risk of epidemics of stem rust in this epidemiological zone. Based on the historical events and predictions, Iran will be one of the frontline countries in the predicated migration route of Ug99. It tooks five years for Yr9-virulent Pst pathotype to reach this country. Conducive environmental conditions exist in Iran and if an epidemic occurs from Ug99 or any variant of Pgt carrying virulence for stem rust resistance gene Sr31 that is present in most of the Iranian wheat cultivars derived from CIMMYT germplasms, serious catastrophic crop losses would be expected.


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