EFFECT OF PEA SEED-BORNE MOSAIC VIRUS ON TWO CULTIVARS OF FIELD PEA GROWN IN MANITOBA

Field plots of Century and Trapper, two cultivars of field pea (Pisum sativum L.) commonly grown in Manitoba, were mechanically inoculated with pea seed-borne mosaic virus (PSbMV) when plants were at the 6-, 8- or 13-node stages. Growth stage at time of inoculation did not significantly affect seed yields or levels of virus transmission through seed of either cultivar. Average yields of plots inoculated at all three stages were reduced 8 and 10% in Trapper and Century, respectively. In both cultivars, yield reductions were attributable mainly to reductions in seed weight. Transmission of PSbMV through seed from inoculated plots of Century and Trapper averaged 0.5 and 5.8%, respectively. In both cultivars, cracked seed coats were most prevalent in seeds from plots inoculated at the two youngest stages of growth. The preceding yield loss values are probably lower than those actually attributable to PSbMV infection, since the virus infected a substantial proportion of control plants (presumably as a result of aphid transmission) and did not infect all inoculated plants. Consequently, an equation was derived for estimating the average yield loss of infected plants. According to this equation, PSbMV infection reduced yield by 11% in Trapper and 36% in Century.