The epidemiology of tomato mosaic: Sources of TMV in commercial tomato crops under glass

Of the several possible sources of tomato mosaic virus, seeds and root debris in the soil are considered to be of greatest importance. A survey of 374,000 seedlings on ten commercial holdings found 0.05% of them infected, and although these were removed virus had been spread to other young plants which did not show infection when transplanted into the growing houses, seven of twenty-two of which contained a few infected plants when sampled shortly after planting. Virus overwintering on clothing, and debris on structures, are thought to be of minor importance, and smoking tobacco is seldom a source of infection for the tomato crop. A further survey of seventy-eight samples from tomato crops in Britain confirmed the 1960-61 survey: all were infected with tomato strains of TMV, none with tobacco strains, but one of the 187 infected seedlings referred to above was carrying a tobacco strain. Petunia was not as satisfactory as a special cultivar of White Burley tobacco for distinguishing between the tobacco and tomato TMV isolates. Observations and tests on a commercial holding showed that TMV was readily carried from plants in infected glasshouses into clean ones by workers, and once introduced, spread rapidly within the crop.