Diversity and Aggressiveness of Rhizoctonia spp. from Nebraska on Soybean and Cross-Pathogenicity to Corn and Wheat

Rhizoctonia and Rhizoctonia-like species of fungi that cause disease are known to have varying host ranges and aggressiveness. Accurate identification of these species causing disease is important for soybean disease management that relies upon crop rotation. The anamorphic genus Rhizoctonia contains several diverse species and anastomosis groups (AGs) including some known soybean pathogens, such as Rhizoctonia solani, whereas for others the ability to cause disease on soybean has not been well described. The present study was conducted to identify the predominant species and AG of Rhizoctonia from soybean, corn, and wheat fields that are pathogenic on soybean and characterize cross-pathogenicity to common rotational crops, corn and wheat. We surveyed for Rhizoctonia spp. in Nebraska; isolates were identified to species and AG, and aggressiveness was assessed. A total of 59 R. zeae isolates, 49 R. solani, nine binucleate Rhizoctonia, three R. circinata, and two R. oryzae isolates were collected in 2016 and 2017 from a total of 29 fields in 15 counties. The most abundant R. solani AGs were AG-4, AG-1 IB, AG-2-1, AG-3, and AG-5. R. solani AG-4 and R. zeae were found in all three regions of the state (west, central, and eastern). Some isolates that were most aggressive to soybean seedlings were cross-pathogenic on both wheat and corn. In addition, R. zeae was pathogenic on soybean when evaluated at 25 degrees C, which is warmer than temperatures used previously, and isolates were identified that were aggressive on soybean and cross-pathogenic on both corn and wheat.