Effect of Temperature and Zinc on Development of Tobacco-Mosaic Virus in Resistant and Susceptible Tomatoes

An investigation of the effects of temperature and of zinc on the development of tobacco-mosaic virus (TMV) in resistant and susceptible varieties of tomatoes was conducted under greenhouse conditions. The study included two experiments, one run during late winter and early spring, and the other during late spring and summer, 1963. Each experiment comprised four treatments and two temperatures. The tomato lines Hawaii 6832, OSU-8, and California 62 PM 22 were used as resistant varieties, whereas the OSU-435-4 line was used as the susceptible one. The common strain of tobacco-mosaic virus was used in this study. Zinc foliar sprays were applied to the tomato plants about 10 days before the seedlings were inoculated with TMV. Immediately after inoculation the plants were divided into two lots and moved to the two temperature houses (cool and hot). The virus concentration was determined by the local lesion assay. One gram of leaf tissue from the tomato plants was ground in a mortar with pestle and a 10-ml. buffer solution added. The extracted sap was squeezed through cheesecloth. One carborundum-dusted leaf of Necrotic Turk tobacco was inoculated. The local lesions were subsequently counted and used as a criterium. Increase in temperature tended to increase virus concentration, although the differences were not significant. Fresh weights of the tomato plants were found to be greater at lower temperatures. Zinc foliar sprays resulted in higher virus concentration and in production of an increased number of local lesions when the inoculum prepared from such treated plants was rubbed into Necrotic Turk tobacco leaves. Effects of zinc on fresh weights were not statistically significant. Zinc applied as foliar sprays appeared to be involved in virus synthesis and multiplication, with higher virus concentrations associated with the addition of zinc. The varieties Hawaii 6832 and OSU-8 were highly resistant, the variety California 62 PM 22 was heterozygous for resistance, and the variety OSU- 435-4 was highly susceptible to the common strain of TMV under the conditions prevailing in these experiments.