The Epidemiology

Abstract

Tomato plants (vars. Moneymaker and Minimonk) inoculated at the cotyledon stage with tomato mosaic virus (TMV) developed about half as much root as did healthy plants, by the time the first trusses were flowering. Although infected plants recovered to some extent, their roots remained 10-25% smaller. Infection at the flowering of the first truss reduced the size of root system by about one-third after 6 weeks, but the plants then recovered. Infection at later stages of growth did not significantly affect root growth. There was no significant relation between the dry weight of the root system and the fresh weight of the top including fruit. Moneymaker and Potentate tomato plants, sown in November, March, June and September, showed similar seasonal changes in the volume of fruit produced weekly, whether or not the plants were healthy or infected with TMV. Infected plants always produced less than healthy ones, but the decrease varied with time of year and age of plant, being greatest in spring and in young plants; the decrease remained fairly steady in older plants. The initial period of acute decrease in volume of fruit production was greater when ovary swelling began early in the year than when it began later. Fewer fruits were produced by infected plants than by healthy ones, except during the winter in var. Moneymaker. During the winter and spring, mean fruit size was decreased by TMV, and was unaffected or increased during the summer and autumn, especially in older plants.