Characterization of three new Yr9-virulences and identification of sources of resistance among recently developed Indian bread wheat germplasm

Detection and characterization of changes in virulence patterns of pathogen populations is a prelude to effective management of wheat rusts. Such information is useful for the identification of sources of resistance, pre-emptive breeding and judicious deployment of resistant wheat cultivars. During 2013-14, three new Yr9-virulent pathotypes (110S119, 238S119 and 110S84) of Puccinia striiformis f. sp. tritici (Pst) possessing combined virulence to cvs Strubes Dickkopf (Yr2, Yr3a, Yr4a) and Suwon92xOmar (YrSU) were detected in India. These pathotypes were more aggressive and virulent than those reported earlier. Riebesel 47/51 (Yr2, Yr9) and Hobbit (Yr14) hitherto resistant to Indian Pst populations, became susceptible to 238S119 and 110S119, respectively. Moreover, the bread wheat cv. HD2967, currently occupying a 10-12 million ha area, showed a high level of susceptibility to these pathotypes. Stripe rust resistance genes, Yr1, Yr5, Yr10, Yr15, Yr24, Yr28 and YrSP were found effective against the new pathotypes. Phylogenetic relationships of the new and nine other closely related pathotypes were elucidated by comparing sequences of the internal transcribed spacer regions. It appeared that pathotypes110S84 and 110S119 were distinct and evolved independently, whereas 238S119 could have evolved from 46S119 by gaining virulence to cvs Strubes Dickkopf and Riebesel 47/51. Recently developed Indian bread wheat germplasm comprising 56 newly released cultivars and 64 advanced lines (2016-17) were evaluated under controlled conditions at the seedling stage for resistance to the three new and the two already known Yr9-virulent pathotypes 46S119 and 78S84. None of the cultivars was resistant to the new pathotypes. Cultivars DBW88, DPW621-50, HD3043, HD3059, HD3171, HS507, HS542, HS562, MACS6478, PBW723, WH1021 and WH1105, resistant to the erstwhile prevalent pathotypes 46S119 and 78S84, showed susceptibility to the new pathotypes. However, 11 advanced bread wheat lines viz. DBW246, HS645, PBW752, PBW757, PBW777, PBW779, PBW780, UP2993, VL1012, VL3013 and WH1233 were found resistant to all the test pathotypes.