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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Soil Management and Sugarbeet Research » Research » Publications at this Location » Publication #311400
Title: Preparation of inoculum of Rhizoctonia solani Kühn for an artificially inoculated field trial

Author
item Vagher, Travis
item FENWICK, ANN - Beet Sugar Development Foundation
item Panella, Leonard

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/3/2014
Publication Date: 12/5/2014
Citation: Vagher, T.O., Fenwick, A., Panella, L.W. 2014. Preparation of inoculum of Rhizoctonia solani Kühn for an artificially inoculated field trial. In: Proceedings of Papers. 74th IIRB Congress, July 1-3, 2014, Dresden, Germany. p. 137-144.

Interpretive Summary: Rhizoctonia crown root and rot is a serious disease resulting in substantial economic losses in sugar beet production worldwide. A consistent, uniform disease pressure of the correct intensity is necessary to effectively screen sugar beet for resistance to Rhizoctonia crown and root rot in an artificially inoculated field trial. This study examined the substrate used to grow the inoculum, the method of producing inoculum and how infective the different particle sizes within the inoculum were. It was found that particles greater than 0.425 mm were the best sources of inoculum and provided constant flow through the applicator used to inoculate the field plots. The smaller particle sizes did not contain adequate amounts of the rhizoctonia pathogen, contained substantial contaminating bacteria or fungi, and caused uneven rate of flow during distribution. We found hull-less barley the best performing substrate to inoculate with Rhizoctonia solani (which causes rhizoctonia crown root and rot). The techniques described have increased the efficiency of inoculum production, decreased losses due to contamination, and guarantee a homogeneous inoculum in size and disease potential, which results in a uniform, consistent field infection.

Technical Abstract: Rhizoctonia crown root and rot, caused by Rhizoctonia solani Kühn, is a serious disease resulting in substantial economic losses in sugar beet production worldwide. A consistent, uniform disease pressure of the correct intensity is necessary to effectively screen sugar beet for resistance to Rhizoctonia crown and root rot in an artificially inoculated field trial. This study examined the substrate used to grow the R. solani inoculum, the method of substrate inoculation, and the pathogenicity of the different particle sizes within the inoculum. It was found that particles greater than 0.425 mm were the most consistently colonized and provided constant flow through the Gandy™ applicator, which is used to inoculate the field plots. The smaller particle sizes did not contain adequate amounts of the pathogen, contained substantial amounts of contaminating bacteria or fungi, and contributed to a varied rate of flow during distribution. We found hull-less barley the best performing substrate to inoculate with Rhizoctonia solani, and a liquid suspension of the pathogen in potato dextrose broth provided uniform colonization of the autoclaved barley during the incubation period. Mushroom spawn bags provided the ideal environment to reduce contamination and insure rapid colonization of the barley grain. The techniques described have increased the efficiency of inoculum production, decreased losses due to contamination, and guarantee a homogeneous inoculum in size and disease potential, which results in a uniform, consistent field infection.