STUDIES ON OVERWINTERING OF TOMATO MOSAIC IN ROOT DEBRIS

Experiments have shown that tomato mosaic virus (TMV) although eliminated from thin tomato roots at temperatures of 180°F (82·2°C) for 10 min, can withstand 212°F (100°C) for 15 min in thick roots. Storage of infected roots for five months resulted in a decrease in virus concentration but TMV was not eliminated from these roots by treatment at 180°F (82·2°C) for 15 min. A survey of commercial soil–treatment on 24 nurseries all using methods of steam sterilization showed considerable variation in results. On many nurseries the temperatures achieved were not high enough to eliminate TMV from root debris. Tests of debris collected from 13 tomato nurseries showed the presence of TMV in all samples but one. A steam and air mixture treatment of soil on a tomato nursery did not eliminate TMV. The development of tomato mosaic was recorded on four nurseries. Infection of most of the Plants resulted from spread from a small number of infected Plants which were found within the first 4–6 wk from planting. On one nursery the distribution suggested that the main source of the virus was soil‐borne inoculum. It is suggested that the rapid increase in the numbers of Plants showing symptoms in early May is the direct result of increased handling of the crop when harvesting begins in April. Copyright © 1969, Wiley Blackwell. All rights reserved