Diversity of Binucleate Rhizoctonia spp. and Population Structure of AG-A in Serbia

From 2013 to 2021, 112 binucleate Rhizoctonia spp. (BNR) isolates were obtained from the strawberry, tomato, pepper, bean, apple, cherry, meadow grass, and soil previously cropped with strawberries from 16 locations in Serbia. Morphological and molecular analyses (ITS, LSU rDNA, RPB2, tef-1α, and atp6) confirmed infections caused by four BNR AGs: AG-G on the cherry (globally new host), bean, and tomato; AG-U on meadow grass (globally new host) and apple, AG-A on the strawberry (the most frequently isolated), and AG-F on pepper. ITS sequence analysis revealed 24 haplotypes within the worldwide population of BNR AG-A, with Serbian isolates belonging to nine. The aggressiveness of AG-A (ten isolates), AG-G (three isolates), AG-F (one isolate), and AG-U (two isolates) was tested on seedlings of 14 hosts from Poaceae, Brassicaceae, Solanaceae, Asteraceae, Fabaceae, Cucurbitaceae, Apiaceae, and Chenopodiaceae, and on detached leaf petioles of the strawberry, tomato, sunflower, and bean, as well as on two pea cultivars. Sunflower and sugar beet were the most susceptible, with AG-G being the most aggressive and AG-A the least aggressive. AG-A could not infect cabbage, while at least one isolate of each remaining AG infected all tested hosts. The consistency between seedling and petiole tests highlights the latter as a rapid method for evaluating the pathogenicity and aggressiveness of BNR isolates.