Effect of temperature on symptom expression of tomato spotted wilt virus in cucumber and Nicotiana glutinosa

Abstract

Young seedlings of cucumber (cotyledon stage) and Nicotiana glutinosa(5-6 and 8-10 leaf stage) were inoculated with TSWV by the conventional leaf rubbing method. The inoculated plants were transferred into each of four incubators at 32, 26, 20 and 16 C. The number of diseased plants and number of leaves with symptoms per plant were counted until 20 days after the inoculation.
At a higher temperature, the test plants developed symptoms rapidly and a high degree of disease incidence. Cucumber exhibited severe symptoms and stunted growth at 32 C while no symptoms were observed at 16 C. N. glutinosa (5-6 leaf stage) inoculated with the virus and kept at 32 C showed severe symptoms and the yellowish color developed under the leaves expanded to the whole plant which eventually died. Leaf symptoms were slight at 16 C. N. glutinosa(8-10 leaf stage) showed the same symptoms, but the plant did not die at 32 C and symptoms on leaves did not appear at 16 C.
To study the effect of changes in the temperature on the symptom expression in N. glutinosa, the inoculated plants were shifted from incubators at higher (32 C) to incubators at lower temperatures (20 C) and from incubators at lower to incubators at higher temperatures at 1, 2 and 4 days after the inoculation. The plants maintained at a higher temperature continously expressed symptoms followed by the plants which remained for a longer period and were shifted early to incubators at high temperature.