Analysis of Rhizoctonia solani isolates associated with sugar beet crown and root rot from Serbia

Rhizoctonia solani is one of the most important sugar beet pathogens worldwide with anastomosis groups (AGs) 2-2 and 4 as the most pathogenic strains on sugar beet. AG 2-2 (intraspecific groups IIIB and IV) can cause both root and crown rot and damping-off, while AG-4 is typically associated only with seedlings damping-off. A total of 20 isolates of Rhizoctonia spp. from sugar beet roots, showing characteristic crown and root rot symptoms, were collected from 4 localities in Serbia. Regarding colony morphology and cultural characteristics, they were divided into 2 groups, which corresponded to their pathogenic, anastomosis and molecular traits. Sequence analysis proved that the first group of isolates were closely related (sequence homology 100%) to AG-4, subgroup HG II, whereas the second group was determined to belong to AG 2-2 IIIB (sequence homology 99%). These two groups differed in range of hosts and in disease intensity on sugar beet, bean and soybean plants. This is the first detailed report on R. solani anastomosis groups that cause sugar beet crown and root rot in Serbia.