VIRULENCE OF PUCCINIA-HORDEI ON BARLEY IN NEW-ZEALAND FROM 1990 TO 1993

Leaf rust of barley (Hordeum vulgare L.), caused by Puccinia hordei Ot th. is common in New Zealand. It is particularly prevalent in the Cant erbury region of the South Island. In a virulence survey carried out b etween 1990 and 1993 to determine the extent of pathogenic variation i n the population of P. hordei in New Zealand, four virulence patterns were detected amongst 187 isolates from barley. All isolates were viru lent on the genes Pa, Pa-2, Pa-4, Pa-6, Pa-9, and Pa-12, and avirulent on Pa-7. Eighteen, 10, and 99% of isolates were virulent on the genes Pa-3, Pa-5, and Pa-8 respectively. No isolates were virulent on the c ombination of Pa-3 and Pa-5. It is postulated that the barley cultivar 'Liberty' relies on the gene Pa-3 for its resistance to leaf rust. Th is 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 virulen ces respectively.