VIEW ARTICLE

Properties of the Initial Tobacco Mosaic Virus Infection Sites Revealed by Heating Symptomless Inoculated Tobacco Leaves. J. A. Foster, Department of Plant Pathology, Cornell University, Ithaca, New York 14850, Present address of senior author: Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; A. F. Ross, Department of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 65:610-616. Accepted for publication 2 January 1975. DOI: 10.1094/Phyto-65-610.

Heat-induced tobacco mosaic virus (TMV) lesions in inoculated Turkish tobacco (Nicotiana tabacum) leaves proved usable in some common procedures requiring local lesions, as well as in studies on the characteristics of symptomless virus infections. In the range where lesion number was inversely proportional to inoculum dilution, quantitative assays of infectivity by the two-dilution method had the same level of accuracy usually observed with assays on conventional local lesion hosts. The susceptibility of Turkish tobacco leaves to TMV inoculation, in terms of heat-induced lesion number per unit leaf area, proved to be unaffected by leaf age or by trimming the plants to two leaves before inoculation. The size of the heat-sensitive area 2 or 3 days after inoculation indicated that cell-to-cell TMV movement in inoculated Turkish tobacco leaves is increased by increases in air temperature (20-30 C) and by trimming the plant before inoculation, but is unaffected by leaf age and by differences in light intensity (8,611-21,528 lux), day length (8-16 hours), or relative humidity (35-80%). The extraction of fewer infectious virus particles from heated tissue than from unheated tissue 12 hours after treatment, was the earliest indication that heating had altered treated tissue.