Temperature influence on the rate of passage of cucumber mosaic virus through the epidermis of cowpea leaves

Primary leaves of cowpea were inoculated, detached and incubated on water agar in closed containers at 16°, 20°, 24°, and 28°C. At hourly intervals, a portion of the epidermis was removed from the left half of each of several leaves. The number of lesions produced in unit areas devoid of epidermis was compared with that in equal areas on the opposite leaf half. At any one temperature, lesion numbers increased in the area devoid of epidermis as the time between inoculation and removal of epidermis was extended. Progressively more incubation time, prior to removal of epidermis, was required for any lesions to develop in the stripped areas as the incubation temperature was decreased. Also, progressively more time was required for equal numbers of lesions to develop in stripped and unstripped areas as the incubation temperature was decreased. Results suggest that temperature directly influences rate of virus passage through epidermal cells into mesophyll cells. Optimum temperature for maximum lesion production was 20° while that for the most rapid rate of virus passage through the epidermis was 28°. Results of experiments with leaves intact on the plants indicated that low internal temperatures of leaves diminished the influence of high external air temperatures on rate of virus passage through the epidermis.