Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: 4/26/1999
Publication Date: N/A
Interpretive Summary: The operation of sugarbeet disease nurseries incurs considerable cost in time and in personal and financial resources. In addition, field nurseries are subject to climatic catastrophes such as drought and flooding. The ability to reproduce in growth chambers or greenhouses sugarbeet disease symptoms caused by fungi would permit the evaluation of both the natural resistance that exists in certain sugarbeet varieties and the efficacy of chemicals or biological control agents in an environmentally-controlled setting. The present work shows that root rot of sugarbeet caused by the fungus Rhizoctonia solani can be reproduced in greenhouse-grown sugarbeet plants. Moreover, resistant varieties of sugarbeet exhibit this resistance in the greenhouse, validating the technique for the screening of sugarbeet varieties to examine that level of root rot resistance that they possess. The method will be used in our lab to identify resistant sugarbeet roots among families that have common parents. This will permit the genes involved in the root rot resistance to be identified, when DNA fingerprinting technologies are applied to the study. The result will be of use to sugarbeet breeders as they strive to produce disease resistant sugarbeet varieties in a more efficient manner.
Technical Abstract: Evaluation of sugarbeet for resistance to Rhizoctonia root rot using field nurseries can be costly and subject to environmental variables that resist disease development. A rapid method for the detection of resistance to Rhizoctonia root rot in sugarbeet in the greenhouse was developed. Sterile barley grain inoculated with an isolate of Rhizoctonia solani AG2-2 (R9 isolate) known to cause root rot in sugarbeet is the basic inoculum. Infested grain is used to inoculate 5 week-old sugarbeet plants in the greenhouse and evaluation of root rot severity is determined at 2-3 weeks post-inoculation. Sugarbeet germplasm from the USDA Fort Collins breeding program and one commercial hybrid were used to validate the method and included highly resistant material (FC709-2 and FC718) and highly susceptible material (FC403, FC607, and Maribo 'Ultramono'). Ranking of the germplasm accessions for percent healthy roots after inoculation in the greenhouse was similar to the ranking of the same germplasm in the Rhizoctonia root rot nursery in Fort Collins over several years of testing. The method can be used for the selection of individuals exhibiting superior root rot resistance from a segregating population. Evaluation of progeny in a segregating population using the assay can improve the accuracy of root rot resistance scoring for use in molecular marker mapping programs. A preliminary characterization of resistance gene candidates (RGSs) amplified by the polymerase chain reaction that differ between plants exhibiting root rot resistance and root rot susceptibility is presented.