Bean yellow mosaic potyvirus infection of alternative annual pasture, forage, and cool season crop legumes: susceptibility, sensitivity, and seed transmission

Seven field and 5 glasshouse experiments were done during 1994-98 to determine the relative susceptibilities and sensitivities of a wide range of alternative annual pasture, forage, and crop legumes to infection with isolate MI of bean yellow mosaic virus (BYMV). Seed harvested from some species was also tested for seed transmission of the virus. Seven of 18 genotypes belonging to 17 species of annual pasture and forage legumes evaluated in 2 replicated field experiments were ranked as highly susceptible to BYMV, 7 as susceptible, 2 as moderately resistant, 1 as resistant, and 1 as highly resistant. The most susceptible and sensitive were Biserrula pelecinus, Trifolium cherleri, T. incarnatum, and T. spumosum. Ornithopus sativus was resistant but sensitive, whereas Hedysarum coronarium was highly resistant. H. coronarium was not infected when manually inoculated repeatedly with 3 different BYMV isolates. Seventy-three of the 94 genotypes of 7 crop legume species tested in the same replicated field experiments were ranked as highly susceptible, including 58/68 of Lens culinaris. Of the remaining genotypes, 6 were susceptible, 5 moderately resistant, 9 resistant, and 1 highly resistant. Five other crop legumes were included in other field experiments in which these species were ranked as highly susceptible (1) or resistant (4). Overall, the most susceptible and sensitive crop legume species were Lens culinaris (most genotypes), Lathyrus cicera, L. ochrus, and Vicia narbonensis. Lathyrus sativus (3 genotypes only), V. sativa (4 genotypes), Cicer arietinum, Pisum sativum, and V. faba were resistant to isolate MI, and Lens culinaris ILL7163 was highly resistant. When infected, C. arietinum was ranked as highly sensitive but symptoms within the other resistant crop species varied in sensitivity between genotypes. Extreme resistance was confirmed in Lens culinaris ILL7163 when it was manually and aphid-inoculated repeatedly with 3 different BYMV isolates. When testing seedlings for seed transmission of BYMV, germination on moist paper towels before testing usually proved more effective than growing in soil in the glasshouse. Low rates of seed transmission of BYMV (0.03-1%) were detected in 9 alternative pasture or forage and 3 alternative crop legume species. This is the first report of seed transmission of BYMV in these species. The pasture or forage species with the highest seed transmission rates were T. clypeatum and T. spumosum (both 1%). The crop legume species in which seed transmission was found were L. cicera (0.1%), L. sativus (0.2%), and V. sativa (0.5%). The high susceptibility and sensitivity to BYMV in some alternative annual pasture, forage, and crop legumes is a cause for concern, especially when they are intended for sowing in BYMV-prone high rainfall zones. Seed transmission of BYMV also leads to inadvertent introduction of the virus to new sites.