Agropyron scabrum and its role in the epidemiology of Puccinia graminis in north-eastern Australia

Abstract

The perennial A. scabrum var. plurinerve is an important graminaceous host for P. graminis f. sp. tritici in north-eastern Australia. Rust uredosori were present on the grass in at least some localities during a 3-year period. The grass is of particular significance in the oversummering of P. grarninis f. sp. tritici, supplementing survival on volunteer cereals.

Two distinct forms of the variety plurinerve have been identified. One is largely confined to the heavy black clay soils of the Darling Downs and parts of northern New South Wales and is of particular importance in the epidemiology of P. graminis.

P. graminis f. sp. tritici, P. graminis f. sp. secalis, and a range of intermediate types occur on the grass, which is apparently a convenient site for somatic hybridization between different formae speciales and strains of P. graminis. P. graminis f. sp. tritici is particularly prevalent on the grass during the summer while the wheat-avirulent intermediate types normally predominate during the balance of the year. The occasional isolation of older strains of P. graminis f. sp. tritici from A. scabrum var. plurinerve suggests that development on the grass acts to some extent as a gene reservoir for the rust population.