Virulence ofPuccinia hordeion barley in New Zealand from 1990 to 1993

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Abstract
Leaf rust of barley (Hordeum vulgare L.), caused by Puccinia hordei Otth. is common in New Zealand. It is particularly prevalent in the Canterbury region of the South Island. In a virulence survey carried out between 1990 and 1993 to determine the extent of pathogenic variation in the population of P. hordei in New Zealand, four virulence patterns were detected amongst 187 isolates from barley. All isolates were virulent on the genes Pa, Pa2, Pa4, Pa6, Pa9, and Pa12, and avirulent on Pa7. Eighteen, 10, and 99% of isolates were virulent on the genes Pa 3 Pa 5, and Pa8 respectively. No isolates were virulent on the combination of Pa 3 and Pa 5 It is postulated that the barley cultivar ‘Liberty’ relies on the gene Pa3 for its resistance to leaf rust. This is the first record of virulence on Pa 3 and Pa 12 in New Zealand. The cultivars ‘Liberty’ and ‘Triumph’ (which contains Pa 12) provided selection pressure for the spread of pathotypes with these two virulences respectively.