Physiologic specialization and new virulences of Puccinia graminis f sp tritici causing black rust of wheat (Triticum aestivum) in India during 2005-2009

During 2005-09, black (stem) rust of wheat (Triticum aestivum L.) was observed mainly in the Nilgiri hills (Tamil Nadu) and in Karnataka. Low incidence was also observed in Madhya Pradesh, Maharashtra and Gujarat, whereas black rust was observed in North Indian hills in Almora (Uttarakhand) and in summer crop in Himachal Pradesh in 2007. More than 300 samples of black rust of wheat were analyzed mainly from Nilgiri hills (Tamil Nadu) and Karnataka. Pathotypes 62G29 (40A) with virulence to Sr2, Sr5, Sr7b, Sr8a, Sr8b, Sr9b, Sr9e, Sr11, Sr28 and 62G29-1(40-1) similar to 40A but with additional virulence to Sr24 were predominant in Nilgiri hills. The frequency of pathoype 62G29-1 (virulent on Sr24) showed increasing trend in Tamil Nadu. Predominant pathotypes 166G2(117-1), 167G3(117-3) and 58G13-3(40-2 in Karnataka appear to be especially virulent on durum and dicoccum wheat. Four new pathotypes were identified during this period including virulence for Sr25 which was resistant till now. New pathotype from Maharashra is virulent to Sr5, Sr8a, Sr9b, Sr9e and Sr11. Three pathotypes, virulent to Sr5, Sr8a, Sr9b, Sr9e, Sr28 and Sr30 were identified from Karnataka where other Sr genes namely, Sr11 and Sr36 were also affected. Black rust resistance genes Sr26, Sr27, Sr31, Sr32, Sr33, Sr35, Sr39, Sr43 were effective and are resistant to all the pathotypes of black rust in India.