Evaluation of resistance of some sugar beet cultivars to leaf spot (Cercospora beticola) disease under greenhouse Conditions

 Leaf spot is the most important disease of sugar beet around the world. It is prevalent in areas with hot and humid weather. Damage to leaves is associated with a decrease in root and sugar content which results in lower root and white sugar yields. This study was conducted as a factorial experiment in a completely randomized design in laboratory and greenhouse of the Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardebili in 2017. Experimental factors included Leaf spot disease in two levels (control, disease) and 11 cultivars (Cesira, Lisetta, Antek, BTS 853, Merak, Yasmene, Qualita, SB16, 25447-79, 25448-79, HI 0063) of sugar beet. Results showed a direct connection between the incubation period and the first day of the onset of symptoms. The first infected spot was recorded eight days after incubation equal to 12.26 ° C for the HI 0063 cultivar. Moreover HI 0063 cultivar had the shortest incubation period (of 137.17° C), and the shortest day of the onset of symptoms (5.9 days). The highest number of spots (405.33) was obtained by the 25748 Cultivar and smallest number of spots (18.08) was recorded by the Merak cultivar. Also the Merak cultivar had the largest stain diameter (905.1 mm), while highest percentage of plant infection (31.75%) and lowest percentage of plant infestation (27.93%) was observed by HI 0063, and SB16 cultivars respectively. The results of cluster analysis of resistance to disease showed that the cultivars were divided into 4 groups, HI 0063 cultivar in one group, Antek, 25448, Qualita and BTS 853 cultivars in another group, the cultivars of Cesira, Yasmene and Lisetta in the third group and SB16, 25447 and Merak cultivars were in the last group. In this study, the sensitive cultivar of HI 0063 had the shortest time for incubation period, the day of symptom emergence, the highest number of blemishes and percentage of plant infestation. The overall results of this study showed that all of the studied traits were involved in resistance except in exceptional cases, increasing degree of resistance, increased the length of the incubation period and decreased the density of the stain per unit area, the diameter of the stain, the percentage of the infected leaves and the number of spores produced in the surface of the stain. Also there was a direct connection between resistance and disease, incubation period and other traits examined. In conclusion, the resistant varieties to disease had the longest time for incubation period, the first day of symptom emergence, the lowest number of spots and percentage of plant infections. However, sensitive varieties had the shortest time for incubation period and the day of symptom emergence and the lowest number of spots and percentage of plant contamination. Accordingly, the HI 0063 cultivar was the most sensitive cultivar and SB16, 25447 and Merak cultivars were resistant cultivars.