SCREENING OF SUGAR BEET CULTIVARS FOR RESISTANCE TO IRANIAN ISOLATE OF BEET SEVERE CURLY TOP VIRUS USING AN INFECTIOUS CLONE OF THE VIRUS

In order to evaluate the effect of sugar beet genotype and method of plant inoculation on resistance to Iranian isolate of Beet severe curly top virus (BSCTV-Ir), a completely randomized experimental design was performed using 18 sugar beet cultivars. Eighteen plants of each cultivar were grown in 6 pots. Two methods of inoculation, namely, agroinoculation using the infectious clone of BSCTV-Ir and inoculation by viruliferous leafhopper (Circulifer haematoceps) were used. The virus replication in inoculated plants was analyzed by PCR, 21 and 35 days post-inoculation (dpi) in the first experiment and 21 dpi in the second experiment. The severity of disease symptoms of inoculated plants was graded using a 0-3 scale (0, symptomless; 1, mild; 2, moderate and 3 severe symptoms). Data analysis of the first experiment indicated that the cv Brigita was the only cultivar in which all the inoculated plants were infected by the virus and all of them showed severe symptoms. Consequently, this cultivar was considered as a highly sensitive control cultivar and used in comparisons. Statistical analysis of the disease symptom severity index showed highly significant differences among cultivars when compared with the control cultivar. As a result, three distinct groups were identified. The first group including the cultivars BR1, FIMMA, HM1990, 7233, and H5505, and the second group including the cultivars Rasoul, Afshari, hybrid of Balk Shiraz, P.P.8, P.P.22, Dorothea, Zarghan, Rhizofouret, IC, Flores, Hilma and Polyrow were regarded as tolerant and sensitive groups, respectively. The third group included only Brigita cultivar which was regarded as very sensitive. Comparison of the data obtained from two inoculation methods indicated that in most cultivars, the virus infection rate was lower with vector inoculation than with agroinoculation.