The epidemiology of tomato mosaic

Publisher Website
Google Scholar
Abstract
SUMMARY: A tomato strain of tobacco mosaic virus infected, on average, about half the cleaned seeds from infected fruits. The proportion differed with tomato cultivar, time of infection and truss. Virus content also varied; seeds usually carried TMV externally, in low concentrations, but about a quarter also carried it within the testa or the endosperm. High virus concentrations sometimes occurred internally, usually when the endosperm was infected. Internal infection decreased, mainly by absence of virus in the testa, as the plant age at the time of infection increased. Endosperm infection occurred mainly in fruits from flowers that set after the plants were infected. The proportion of fruits with seeds was smaller in early infected plants than in those infected later. Fewer necrotic, blackened seeds were obtained from late‐infected plants than from those infected earlier, and more necrotic seeds were infected with TMV than normal ones, especially in the endosperm. Although the embryo was sometimes contaminated during dissection, virus within it was never confirmed. Necrotic seeds often failed to germinate.Treating the fruit pulp with one‐quarter of its volume of conc. hydrochloric acid for 30 min. was the best means of cleaning seeds and of eliminating TMV carried externally. Fermentation and sodium carbonate extraction did not eliminate external TMV. Soaking previously cleaned seeds in 10% Teepol (Shell non‐ionic detergent) solution for 2 hr., or in a 10% tri‐sodium orthophosphate solution for 20 min. also inactivated external virus. The only treatment that often eliminated TMV carried internally was heating dry seeds in an oven at 70d̀C; treatment for 3 days was usually enough to free seeds completely but sometimes 3 weeks would not eliminate all virus, particularly that carried by the endosperm. Such treatments did not affect percentage germination of seeds other than recently harvested ones, but heated seeds sometimes took longer to germinate than unheated ones.TMV was lost within a few months in some stocks of seeds but persisted for at least 9 years in others with endosperm infection. Virus content of seeds fell rapidly for 2 weeks after sowing but then remained at a low level for many weeks. Plants never became infected when allowed to grow undisturbed after the seeds were sown. ‘Seed‐infectio’ occurred only when the seedlings were pricked out (transplanted) and the testas or remaining endosperm were rubbed against the seedlings. The proportion of plants thus infected was usually small because (1) many seeds did not carry virus; (2) virus was rapidly inactivated after sowing; (3) after normal sowing 65% of testas were left behind in the soil when the seedlings were pricked out; (4) very young seedlings resisted infection: and (5) infection was more likely with recently harvested than with older seeds, probably from TMV remaining on the testas. However, all seedlings which were infected, even with dilutions of TMV‐infected leaf sap leaf in water as low as one part in five millions, showed symptoms within 3–5 weeks.