Further studies on Pea seed-borne mosaic virus in cool-season crop legumes: responses to infection and seed quality defects

Abstract

Field and glasshouse experiments (3 of each) were done during 2003–06 to determine the responses of a range of genotypes belonging to 13 species of cool-season crop legumes to infection with Pea seed-borne mosaic virus (PSbMV). Seed quality defects were determined and genotypes of some species were also tested for seed transmission of the virus. In field experiments, of 39 genotypes of field pea (Pisum sativum) evaluated, 15 were ranked as highly susceptible, 10 susceptible, 9 moderately resistant, and 5 resistant, while all 7 lupin species (Lupinus spp.) tested were resistant. In glasshouse sap and graft inoculations with PSbMV to genotypes not found infected in the field and 2 additional lupin species, no virus was detected in any of the 9 lupin species or in 5 field pea genotypes tested. Thus, the lupins all appeared to be non-hosts and the 5 field pea genotypes had resistance to the 2 PSbMV isolates used to inoculate them. All 14 genotypes of faba bean (Vicia faba) evaluated in the field were ranked highly susceptible, while 12 out of 16 lentil (Lens culinaris) genotypes were ranked as highly susceptible and 4 as susceptible. Chickpea (Cicer arietinum) genotypes were moderately resistant (50) or susceptible (7). Once infected, plant sensitivities (symptom severities) ranged from low in some field pea and most lentil genotypes to high in most faba bean genotypes. Chickpea genotypes all were ranked as moderately sensitive. Seed lots harvested from PSbMV-infected plants of field pea, faba bean, and chickpea all showed severe seed quality defects, but lentil was usually less affected. The predominant seed symptoms were necrotic rings and line markings on the seed coat, malformation, reduced size, and splitting. Kabuli chickpea types also showed darkening of the seed coat. Seed transmission of PSbMV was detected in faba bean (0.2%) and field pea (5–30%). When PSbMV infection foci were introduced into plots of lentil cv. Nugget, the virus spread to the lentil plants and decreased shoot dry weight by 23%, seed yield by 96%, and individual seed weight by 58%. Seed transmission of PSbMV (6%) was detected in seed from the infected lentil plants. In a survey for possible viral seed symptoms, all seed lots of kabuli chickpea (5) and field pea (70), and 10 of 18 of faba bean were affected, but none of the 23 of lentil. When seedlings from 16 faba bean and 7 field pea seed lots were tested for 3 viruses, neither Broad bean stain virus nor Broad bean true mosaic virus was detected, but PSbMV was found in 5 field pea seed lots at incidences of <1–14%. PSbMV was detected in commercial field pea seed stocks of cvv. Kaspa (33) and Parafield (12) at incidences of 0.5–47% and 0.3–30%, respectively. The implications of these findings in terms of genotype susceptiblility and sensitivity to PSbMV infection and their importance for the management of PSbMV in legume crops are discussed.