Resistance and virulence patterns in the pea seed-borne mosaic virus (PSbMV) / lentil (Lens culinaris) pathosystem

Pea seed-borne mosaic virus (PSbMV) can reach high levels of seed infection in Australian field peas, resulting in severe crop losses. Endemic, pea-derived PSbMV strains can cause lentil seed infection under experimental conditions, but PSbMV transmission has not been detected in grain harvested from lentil crops in Australia. In contrast, specialised PSbMV strains that are seed-borne in lentils occur in countries with long histories of lentil cultivation. A total of 29 PSbMV isolates were obtained from seeds of 11 exotic lentil accessions held at the Australian Grains Gene-bank, and the isolates were identified as the P2 pathotype using the standard set of pea differentials. However, testing with an additional set of lentil genotypes revealed two distinct pathotypes, tentatively designated P2a and P2b. Screening of lentil accessions previously reported to possess resistance to PSbMV or to bean yellow mosaic virus (BYMV), as well as Australian (25) and North American (3) cultivars, identified resistance to the P2b pathotype in several entries. In contrast, resistance to the more virulent P2a pathotype was only detected in three germplasm accessions that were previously reported to be BYMV resistant. Incursions of lentil seed-borne PSbMV strains pose major risks to the Australian lentil industry. Collaboration with research programmes in countries where lentil seed-borne PSbMV is present will facilitate resistance screening against a possible wider range of pathotypes, and support research on virulence genes and virus genes controlling seed transmission. As large-scale testing with exotic virus strains is difficult to implement in Australia, development of molecular markers for resistance to the most virulent PSbMV strains is desirable.