Investigation on stability of sugar beet parents resistance to curly top

Curly top is one of the important damaging diseases in sugar beet farms in Iran. Introducing the commercial tolerant parent cultivars 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 investigate the tolerance of sugar beet parent cultivats continually. To do this the tolerant parent cultivares (germplasm available in the Institute) along with tolerant source, were studied in the infected field of Fasa area by observation for a period of four years (2000-2003). The aim of this study was to replace cultivar which show sensitivity during the field trials by using parents of other sources, which are more tolerant to curly top disease. In this experiment, nine lines and cultivars (19369-66,16402-66, 16785-67, 16585-67, F- 20311-9825-76, H5505-70, ET5-77, OTYPENB5-75 and MSTNB1-65) were planted, each in two rows of 50 meter long with suitable distances between the rows. After the period of weeding and first thinning, the number of infected and uninfected plants were counted, considering the morphological characteristics of the young plants, the degree of infection was expressed as the percentage 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 that there is a sharp difference in infection degree among the lines and cultivars under study. The data means of the four years observations showed that the cultivar F-20311-9825-76 and the line 16402-66 had the infection degrees of 12.14 and 29.86% respectively. But the amount of root yield and white sugar yield were respectively 60.29 and 7.52(for cultivar F-20311-9825-76) and 62.94 and 7.91 ton.ha-1 (for line 16402-66). The line OTYPENB5 -75, had the highest infection degree to curly top (equal to 37.36%). Considering the results, although the percent of infection to curly top was higher for the line 16402-66 than F-20311-9825-76, but it produced the highest root and white sugar yield, therefor, it is recommended that this line can be used as a tolerant parent. Keywords: Sugar beet, Curly top, Parents resistance, Infection