Effect of Cercospora leaf spot on photosynthetic pigments and antioxidant enzymes activity of different sugar beet varieties

Cercospora leaf spot is one of the most important and common leaf diseases of sugar beet which causes several damages. This study aimed to find indices to distinguish susceptible and tolerant to cercosporaleaf spot sugar beet cultivars. The experiment was conducted in a factorial design based on randomized complete block design under laboratory and greenhouse conditions. Treatments included 11 sugar beet genotypes and contamination and non-contamination to cercospara leaf spot disease treatments. Different traits such as main photosynthetic pigmants (cholorophyll a, b, total cholorophyll and pigment ratio), auxiliary pigments (carotenoids, flavonoids and anthocyanins) and antioxidant enzymes activity such as catalase, proxidase and polyphenol oxidase, and shoot and root dry weight were measured. Results of the main photosynthetic pigments evaluation showed that the disease reduced the chlorophyll a and b  and consequently total chlorophyll content. The amount of photosynthetic auxiliary pigments, except carotenoids, increased as the disease progressed in infected plants. Cercospora leaf spot increased the activity of catalase, peroxidase and polyphenol oxidase enzymes and decreased dry weight of shoot and increased root dry weight with control. Cultivar HI0063 was affected by the disease earlier than other cultivars, and had a higher dry weight loss than other cultivars; also plant weight in this cultivar was higher than other cultivars and higher level of chlorophyll a and flavonoids was seen. The level of antioxidant enzyme activity of HI0063 was higher than the tolerant cultivar. Yasmeneas cultivar as the most tolerant cultivar showed the diseases symptoms later compared with other cultivars with the lowest leaf dry wieght reduction.