The present study was designed to evaluate the characteristics of the incidente of Cercospora leaf spot, caused by Cercospora beticola Sacc. in sugar beet (Beta vulgaris L.) cultivars differing in resistance as affected by the environmental conditions. The trials were conducted during the period 2001–2005 at the Lithuanian Institute of Agriculture in Dotnuva. In the field experiments we grew 5–10 cultivars of sugar beet annually. The cultivars were susceptible or resistant. The disease incidence in resistant cultivars was significantly Po than in susceptible ones, except for the year 2002. The disease Severyty was significantly higher in susceptible sugar beet cultivars (by 29.1 to 89.8%) than in resistant ones. In 2004 and 2005, the epidemic progress of C. Beticola in the B. vulgaris susceptible cultivar Millennium and resistant cultivar Dorena depended on the weather conditions. The first symptoms of the incidente of C. beticola in the susceptible cultivar Millennium appeared two weeks earlier than in the resistant cultivar Dorena. In 2004, in the resistant cultivar Dorena, 50% of plants were affected by C. beticola 20 days later and in 2005 5 days later compared with the susceptible cultivar Millennium. AUDPC (Area Under the Disease Progress Curve) calculated by trapezoid integration in 2004 and 2005 was substantially higher in the susceptible cultivar Millennium than in the resistant cultivar Dorena. The white sugar yields were significantly higher for the resistant sugar beet cultivar compared with the susceptible cultivar in 2001 (12.3%) and 2002 (5.5%). Our results suggest that white sugar content in both sugar beet cultivars was significantly dependent on the disease severity.

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