EFFECT OF TEMPERATURE ON THE INFECTION OF SUGAR BEET PLANTS BY BEET SEVERE CURLY TOP VIRUS AND ON RECOVERY OF VIRUS-INFECTED PLANTS *

The effect of various temperatures on the infection of sugar beet plants by Iranian isolate of Beet severe curly top virus (BSCTV-IR) was evaluated. Presence of BSCTV-IR in agroinoculated plants was assayed at 7, 14 and 21 days post-inoculation (dpi) using PCR. Based on the infectivity assay, the optimum temperature for BSCTV-IR infection was 25C at which the mean period between inoculation and the first virus detection was the shortest and the virus concentration was the highest. No virus was detected in plants incubated at 35C until 21 dpi. To evaluate the effect of temperature on recovery of BSCTV-IR-infected plants, symptomatic plants were incubated at the aforementioned temperatures. The first new leaf showing recovery phenotype emerged 7 dpi at 35 ºC. This period for plants incubated at 30, 25-30, 25 and 20ºC was 12, 18, 25 and 28 days post-incubation, respectively. Thus, recovery occurred faster as the temperature raised. Re-inoculation of recovered plants with the same virus induced no symptoms in newly emerging leaves, indicating the stability of the phenotype of recovered plants against re-infection by the same virus. Quantitative analysis using real-time PCR showed significant decline in viral DNA in either recovered or new leaves emerged after re-inoculation compared to symptomatic leaves.