evaluation of resistance of sugar beet hybrids to curly top virus under field conditions

in order to study the response of new sugar beet hybrids and cultivars to curly top disease in the field conditions, an experiment was carried out in a randomized complete block design with four replications and sixteen treatments in 2007 in fasa. each plot included a hybrid or cultivar planted in three rows with eight meter length and 50cm between- row spacing. after weeding and first thinning, percentages of the infected plants were calculated based on the morphological characteristics of the young plants. disease index was also measured for each treatment. at the end of growth period, the quantity (root yield and white sugar yield) and quality (sugar content) of in all treatments were measured and compared. the results showed that there was a significant difference in the percentage of infected plants and disease index among the hybrids and cultivars (α=1%). two hybrids 28957 and 28914, had the lowest infection percentage and disease index of 3.970, 1.175 and 3.940, 1.280 percentages respectively. cultivars h2301, branco and chinook had the lowest infection percentage and severity to curly top. there was also a significant difference among the hybrids and cultivars regarding root yield, white sugar yield and sugar content (α=1%). the highest root yields(78.57, 77.98 and 71.90 tha-1) and white sugar yield(11.75, 12.27 and 11.55 tha-1) were recorded for h2301, branco and chinook cultivars, respectively. the hybrid 28957 with 9.30 tha-1 white sugar yield was superior to the other hybrids. the maximum sugar content obtained from the cultivar chinook and hybrid 28910, 18.39% and 18.23%, respectively. therefore the hybrid 28957 are recommended as two curly top tolerant hybrids for producing resistant cultivars.