Virulence of isolates of Ustilago tritici collected in Manitoba and Saskatchewan, Canada, from 1999 to 2007

Abstract

Breeding for resistance to the loose smut pathogen, Ustilago tritici, in wheat is a traditional disease management approach in western Canada. The development of resistant wheat lines relies on accurate methods for identification of effective host resistance. Knowledge of the virulence frequencies of races in the pathogen population is essential to identify effective host resistance. The objective of this work was to characterize the virulence phenotypes of U. tritici isolates collected from 1999 to 2007 in Manitoba and Saskatchewan. Sixty-four isolates of U. tritici from durum wheat and 59 from hexaploid wheat were assessed for virulence. Teliospore suspensions of each isolate were injected into florets of the wheat differential host series by needle inoculation at mid-anthesis. Mature seed from inoculated florets were grown to determine the per cent infected plants. Eighty-five per cent of durum wheat isolates were race T32, possessing virulence to differential lines ‘Mindum’ (TD-1), and ‘Wakooma’ (TD-19). Virulence to ‘Pentad’ (TD-11) was found in only 5% of the durum wheat isolates. Races T7, T5, T64 and T10 were the most commonly identified races from the hexaploid wheat isolates of U. tritici. Six previously unreported races were identified: races T61, T64, T65, T66, T67 and T68. None of the isolates possessed virulence to ‘Sonop’ (TD-14), while >50% of the isolates possessed virulence to ‘Kota’ (TD-4), ‘Little Club’/‘Reward’ (TD-5A), ‘Reward’ (TD-7) and ‘Thatcher’/‘Regent’/‘Reward’ (TD-12A). Virulence to TD-6, which was previously uncommon from Manitoba and Saskatchewan, was possessed by 20% of the hexaploid wheat isolates. The natural population of U. tritici in Manitoba and Saskatchewan continues to evolve in terms of virulence, but effective sources of resistance are still currently available.