MULTIPLE VIRAL DETERMINANTS AFFECT SEED TRANSMISSION OF PEA SEED-BORNE MOSAIC-VIRUS IN PISUM-SATIVUM

Two pea seedborne mosaic potyvirus (PSbMV) isolates, P-1 DPD1 (P-1), w hich is highly seed-transmitted, and P-4 NY (P-4), which is rarely see d-transmitted, and chimeras between P-1 and P-4 were analysed to map t he viral genetic determinants of seed transmission, Infectivity of chi meric viruses was evaluated by inoculating Pisum sativum with RNA tran scribed in vitro from recombinant full-length cDNA clones, The chimeri c viruses that were used demonstrated that a genomic segment encoding the 49 kDa protease and putative RNA polymerase was responsible for sy mptom induction, Attempts to determine transmission of the chimeric vi ruses in P. sativum cultivars known to transmit P-1 at high frequencie s showed that seed transmission is a quantitative character influenced by multiple viral determinants, Seed transmission frequency did not c orrelate with accumulation of virus in vegetative tissue. The 5' 2.5 k b of the 10 kb PSbMV genome had a major influence on the seed transmis sion frequency and was analysed further. This showed that, while the h elper-component protease was a major determinant of seed transmission, the potyviral P1-protease exerted no measurable influence.