INTERACTIONS BETWEEN A SEED-BORNE STRAIN OF CUCUMBER MOSAIC CUCUMOVIRUS AND ITS LUPIN HOST

The relationship between time of inoculation with cucumber mosaic cucu movirus (CMV) and the growth, seed production and rate of seed transmi ssion of virus in lupin (Lupinus angustifolius cv. Illyarrie) was stud ied in field-grown plants. Plants inoculated at the seedling stage (2 days post-emergence) showed 45% mortality. Plants infected through the seed were more stunted than plants inoculated at the seedling stage. Plants inoculated up to the mid-vegetative growth stage (58 days post- emergence) yielded less-than-or-equal-to 27% of the dry matter and les s-than-or-equal-to 9% of the seed of healthy plants. Late inoculation (114 days post-emergence) did not affect dry matter yield, but reduced seed yield to 75% of that of healthy plants. Rate of seed transmissio n depended on the time of inoculation of plants. The maximum rate was 24.5% for plants that were inoculated at the mid-vegetative growth sta ge (58 days post-emergence). However, early inoculation caused a large reduction in seed yield, and it was shown that plants inoculated at t he beginning of flowering (94 days post-emergence) produced greater nu mbers of infected progeny than plants inoculated at earlier or later t imes. No relationship was observed between seed weight and transmissio n of CMV. Infectious CMV was recovered from the embryo, but not from t he testa. A simple seed transmission model was used to evaluate severa l hypothetical epidemics and to determine the time of inoculation whic h results in greatest rates of seed transmission of CMV. For example, when fewer than 73% of plants in a crop become infected with CMV, then the rate of transmission of virus in crop seeds will be greatest when inoculations are at the beginning of flowering.