Studies on the effect of temperature on virus multiplication in inoculated leaves

The rate at which the Rothamsted tobacco necrosis virus (RTNV) accumulates in inoculated French bean leaves increases with rising temperature to 22 degrees C. and then decreases. Three days after inoculation, leaves at 22 degrees C. contain 4000 times as much virus as at 10 degrees C. and 1000 times as much as at 30 degrees C. At all temperatures the rate of accumulation may depend on the balance between synthesis and inactivation of RTNV, but inactivation becomes increasingly important with rise of temperature above 22 degrees C. and as the virus content of the leaves increases. Above 22 degrees C. the rate of multiplication may increase but less rapidly than the rate of inactivation, and exposing inoculated leaves to ultra-violet radiation at various intervals after inoculation suggests that at 30 degrees C. RTNV multiplies in and moves from the initially infected epidermal cells in slightly less than the 6 hr. needed at 22 degrees C. Thirty hr. are needed at 10 degrees C. Newly formed virus is rapidly inactivated at 30 degrees C. Raising the ambient temperature also decreases the numbers of local lesions produced by RTNV, possibly by increasing the chances that the introduced virus particles will become inactivated. Increasing the virus content of the inoculum above the level giving one lesion per sq. cm. does not increase the subsequent virus content of inoculated leaves. At temperatures of 30 degrees C. and below, tomato aucuba mosaic virus produces necrotic lesions in leaves of tobacco and Nicotiana glutinosa whereas above 30 degrees C. the lesions are chlorotic. In both hosts this virus multiplies more rapidly when the infected cells are killed.