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Poster: Biology & Disease Mgmt: Mycology


Virulence of Rhizoctonia solani anastomosis groups on cotton, corn, rice and soybean
K. URREA (1), C. Rothrock (1), S. Winters (1) (1) University of Arkansas, U.S.A.

Rhizoctonia solani is an important pathogen on numerous crops. Isolates of R. solani were recovered from major row crops in the southern United States as part of a Rhizoctonia survey, and represented anastomosis groups (AG) 2, 4, 7, and 11. Virulence was evaluated for two isolates of each AG using stand and hypocotyl/coleoptile ratings on soybean, corn, rice and cotton using colonized millet seed inoculum placed 1-cm from seed at the time of planting (seed rot assay) or seedlings 7 days after planting (hypocotyl/coleoptile assay) in controlled environmental experiments at 25°C. Plant stands and discoloration ratings were recorded 7 days after planting or hypocotyl/coleoptile inoculation. In the seed rot assay, isolates of AG2 caused significant stand loss and brown-reddish discoloration of coleoptiles in corn. In cotton, the AG4 isolates were highly virulent causing significant stand loss compared to other AGs. In soybean, there were not significant differences in stands among isolates. In the hypocotyl assay on cotton, AG4 isolates caused significant damping-off. There were no significant differences in number of seedlings for corn, rice or soybeans. In all four crops, AG4 and AG11 isolates caused reddish brown lesions on hypocotyls or coleoptiles. This research supports the results of the soil and crop survey that crop increases the recovery of AGs of R. solani that are virulent on that crop.