Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 2011
Publication Date: March 11, 2011
Citation: Strausbaugh, C.A., Eujayl, I.A., Panella, L.W., Hanson, L.E. 2011. Virulence, distribution and diversity of rhizoctonia solani from sugar beet in Idaho and Oregon. Canadian Journal of Plant Pathology. 33(2): 210-226. Interpretive Summary: Rhizoctonia root rot caused by Rhizoctonia solani is a widespread disease that can attack at least 200 different plant species. On sugar beet, damage can vary from 0 to at least 50% stand loss depending on cropping history and environmental conditions. In order to help explain why Rhizoctonia root rot management practices have not performed well in some areas of the Intermountain West (IMW), a survey was conducted from 2004 to 2006. Most of the isolates collected from sugar beet fell into one of two genetic subgroups, AG-2-2 or AG-4. Isolates in AG-2-2 were the most virulent on sugar beet and some could also attack corn. Some of the AG-2-2 isolates were both more virulent and genetically diverse compared to strains used to screen for Rhizoctonia root rot resistance in sugar beet. Additional investigations will need to be conducted to understand if this genetic diversity and the ability to attack corn are compromising current approaches to managing this disease problem in the IMW.
Technical Abstract: Rhizoctonia root rot causes serious losses on sugar beet worldwide. In order to help explain why Rhizoctonia root rot management practices have not performed well in some areas of the Intermountain West (IMW), a survey was conducted. In the IMW from 2004 to 2006, 94 Rhizoctonia solani field isolates were collected from sugar beet roots. These field isolates were compared with 19 reference strains and 46 accessions from GenBank for genetic diversity based on sequencing of the ITS-5.8S rDNA region. Greenhouse pathogenicity tests on sugar beet and silage corn were conducted and plant damage was assessed using a randomized complete block design with at least four replications. The majority (92%) of the isolates had identity with the AG-2-2 IIIB (48%) or AG-4 subgroups (44%). Isolates from AG-2-2 IIIB were the most virulent on sugar beet and had the most diversity in phylogenetic analysis. Seven (all AG-2-2 IIIB) of 18 isolates tested could attack both sugar beet and corn, with two of the isolates causing less root rot than the others. To reduce Rhizoctonia root rot on sugar beet and corn, crop rotations and the isolates utilized for selecting host resistance could be given further consideration.