Necrotic Lesion Induced by Heat Treatment on Leaves of Systemic Host Infected with Tobacco Mosaic Virus

Abstract

Foster and Ross (1968) found that when Turkish tobacco leaves inoculated with tobacco mosaic virus (TMV) were 2-5 days later immersed for 40sec. in water at 50°C, local lesions appeared 1-2 days after the heat treatment. We determined the conditions for more effectively inducing local lesions, and also compared the modes of infection and multiplication of TMV between systemic hosts and local lesion hosts. N. tabacum ‘Xanthi’and N. tabacum ‘Samsun’ were used as the systemic hosts, and ‘Xanthi nc’ and ‘Samsun NN’ as the local lesion hosts. When leaves of 2.5 months old plants were used, optimum treatment was for 2min. at 50°C, or for 10sec. at 55°C. Optimum incubation after the heat treatment was for 2-3 days at 25°C, or for 1-2 days at 30°C. When leaves of younger plants were used, 1min, treatment at 50°C was adequate, whereas 2min. at 50°C resulted in a visible injury of the treated leaves. In leaves of plants older than 3 months, treatments even longer than 2min. at 50°C induced no lesions at all. The number of lesions induced by heat treatment on leaves of the systemic hosts inoculated with TMV was of about the same level as on leaves of the local lesion hosts inoculated with TMV of the same concentration. There was also no significant difference in virus dilution-infectivity curves between the systemic hosts and the local lesion hosts. No significant difference was observed in the number of ectodesmata in epidermal cell walls of healthy leaves between both hosts. Local lesions on leaves of the systemic hosts induced by heat treatment 2-4 days after inoculation were much larger in size than those on leaves of the local lesion hosts on the same days after inoculation. TMV seemed to spread from each infective center more rapidly in the leaves of the systemic hosts than in those of the local lesion hosts. It is considered that the numbers of infectible sites are about equal between the local lesion hosts and the systemic hosts, but the rate of TMV multiplication after the establishment of infection is lower in the local lesion hosts than in the systemic hosts.