COMPARISON OF SOME PEA SEED-BORNE MOSAIC-VIRUS ISOLATES AND THEIR DETECTION BY DOT-IMMUNOBINDING ASSAY

Five isolates of pea seed-borne mosaic virus (US, S4, S6, Q and T) were compared by host range and symptomatology on 16 Pisum sativum cultivars and lines, 21 lines of Lathyrus and Lens spp. and several indicator species. All selections of Pisum sativum, except cv. Greenfeast, were susceptible to all isolates, but Greenfeast was susceptible to the US isolate. All isolates except T infected the Lathyrus and Lens spp. through mechanical and aphid transmissions. Chenopodium amaranticolor and Vicia faba reacted similarly to all isolates, Phaseolus vulgaris cv. Hawkesbury Wonder reacted to none. The North American isolate (US) was distinguished from the Australian S4, S6, Q, and T isolates by infecting Nicotiana clevelandii and Greenfeast pea. In all cases the highest rate of seed transmission occurred in the largest seed (82-91%) and the lowest was in the smallest seed (27-40%). Infected seed in the largest size classes was lighter in weight than the corresponding uninfected seed. Infected seed in all classes had a significantly lower germination rate than uninfected seed although the greatest reduction in germinability was in the smallest seed. In each size class uninfected seed was heavier than infected seed and germinated better. Two-dimensional immunodiffusion tests showed that precipitin lines between all the isolates and either the US and S6 antisera were confluent with no evidence of spurs. A rapid and sensitive indirect dot-immunobinding assay on nitrocellulose membrane for PSbMV was developed in which non-specific reactions were eliminated by using mannose and glucose in buffers, and healthy plant sap as a blocking agent. The limit of detection of antigen was about 32 ng per sample. Both of the antisera detected antigen in sap extracted from peas infected with the 6 PSbMV isolates, originating from the USA, Australia, New Zealand and Denmark and all isolates were detected at similar antiserum dilution endpoints.