Evaluation of sugar beet cultivars for resistance to curly top virus disease.

Curly top is one of the important damaging diseases in sugar beet farms in Iran. Introducing the commercial tolerant varieties is considered as the most economic way for the disease control. According to the litterature, there is always the risk of tolerance breakdown in the improved cultivars, So it is essential to evaluate the tolerance of sugar beet varieties. To do this the tolerant cultivares (germplasm available in the Institute) along with tolerant source, were studied in the infected field in Fasa .Six treatments were studied in a randomized complete block design with four replications in 2005. The aim of this study was to determine the most resistant variety suitable for the region. In this experiment, cultivars (F-20634-H2301, 16396-66, 13687-62, 16402, H5505 and RASOUL) were planted, in three rows with 50 centimeters distances between them. After weeding and first thinning, the number of infected and uninfected plants were counted, considering the morphological characteristics of the young plants, and the degree of infection was expressed as the ratio of infected to the uninfected plants. At the end of growing period, the quantitative and qualitative characteristics including: root yield, sugar content, white sugar percent, white sugar yield, purity of raw extract and impurities (K, Na and N content) of the roots, alkali index and molasses were measured and recorded.The results showed sharp difference in infection degree among the cultivars under study. The data means of the one year showed that the cultivar F-20634- H2301 had least infection percent (4.70%). The cultivar 13687-62 , had the highest infection degree to curly top (22.22%). There were significant difference among different cultivars regarding root yield and white sugar yield at 1% probability level. Highest root yield and white sugar yield were recorded for F-20634-H2301 cultivar as 55.83 and 7.84 ton.ha-1 , respectively. Root yield and sugar yield of Iranian tolerant cultivar H5505 were equal to 50.83 and 6.03 ton.ha-1 , respectively. There were no significant difference for yield components including sugar content , white sugar percent, purities, Na and K paste extracted from sugar beet root among different cultivars. Considering the results, the percent of infection to curly top was lowest for F- 20634-H2301, cultivar, it also produced the highest root and white sugar yield, therefore,it is recommended as a tolerant cultivar.