Virulence of Puccinia triticina on wheat in Iran.

Abstract

Wheat leaf rust is controlled mainly by race-specific resistance. To be effective, breeding wheat for resistance to leaf rust requires knowledge of virulence diversity in local populations of the pathogen. Collections of Puccinia triticina were made from rust-infected wheat leaves on the territory of Khuzestan province (south-west) in Iran during 2008 - 2009. In 2009, up to 20 isolates each of the seven most common leaf rust races plus 8 -10 isolates of unnamed races were tested for virulence to 35 near-isogenic wheat lines with different single Lr genes for leaf rust resistance. The lines with Lr9, Lr25, Lr28 and Lr29 gene were resistant to all of the isolates. Few isolates of known races but most isolates of the new, unnamed races were virulent on Lr19. The 35 Lr gene lines were also exposed to mixed race inoculum in field plots to tests effectiveness of their resistance. No leaf rust damage occurred on Lr9, Lr25, Lr28 and Lr29 in the field, and lines with Lr19, Lr16, Lr18, Lr35, Lr36, Lr37 and the combination Lr27 + Lr31 showed less than 15% severity. A total of 500 isolates of P. triticina obtained from five commercial varieties of wheat at two locations in the eastern and northern parts of the Khuzestan region were identified to race using the eight standard leaf rust differential varieties of Johnson and Browder. Thirteen known wheat leaf rust races and several new, unnamed races were identified. The most common races in each year were races 57, 64, 84, 143 and 167. Key words: Puccinia triticina, wheat leaf rust, specific resistance.