Diversity and Aggressiveness of Rhizoctonia solani and Rhizoctonia-like Fungi on Vegetables in New York

Vegetable growers in New York, especially those growing table beets, have recently observed that the corn rotation is no longer effective in suppressing diseases caused by Rhizoctonia solani and Rhizoctonia-like fungi. To investigate this problem, 68 isolates of Rhizoctonia solani and Rhizoctonia-like fungi infecting vegetables in New York were isolated, characterized, and their pathogenicity on corn determined. Sequence analysis of the rDNA internal transcribed spacer region inferred 26 isolates to belong to R. solani anastomosis group (AG) 2-2 and 19 isolates to belong to AG 4. Remaining isolates belonged to AG 1, AG 2-1, AG 5, AG 11, Ceratobasidium AG (CAG) 2, CAG 6, and Waitea circinata var. zeae. This is a first report of AG 11 and W. circinata var. zeae recovered from naturally infected vegetables in New York. Pathogenicity tests on corn showed that the majority of isolates are pathogenic on corn, and isolates belonging to AG 22, AG 5, and AG 11 exhibited high aggressiveness. These results suggest that certain strains of R. solani and Rhizoctonia-like fungi infecting vegetables in New York have acquired the ability to infect corn. In addition, snap bean was inoculated with seven isolates exhibiting low to high aggressiveness on corn, and a correlation between aggressiveness on corn and snap bean was observed.