Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2001
Publication Date: 5/7/2001
Citation: Panella, L.W. 2001. Publicly released sugar beet germplasm evaluated for resistance to rhizoctonia-root-rot, 2000.. Biological and Cultural Tests for Control of Plant Diseases. Interpretive Summary: The USDA-ARS Sugar Beet Research Unit in Fort Collins, CO has been developing sugar beet germplasm with resistance to various diseases for the last 30 years. Over this time, several sugar beet germplasm have been released while others are still being developed. In 2000, 37 of these sugar beet germplasm were tested for resistance to Rhizoctonia root rot. Due to high temperatures and a high inoculum pressure, the disease progressed quickly and was severe. A number of the germplasm tested performed as well as did the resistant and highly resistant controls.
Technical Abstract: Thirty-seven sugar beet germplasm released over the past 30 years, or under development by the USDA-ARS Sugar Beet Research Unit located in Fort Collins, CO were evaluated for resistance to Rhizoctonia root rot in Windsor, CO. Plants were inoculated with dry, ground, barley-grain inoculum of Rhizoctonia solani. Immediately after inoculation, a cultivation was performed to throw soil into the beet crowns. Beets were harvested and each root was rated for rot on a scale of 0 (no damage) to 7 (dead). Analyses of variance were performed on disease indices (DIs), percent healthy roots (undamaged classes 0 and 1 combined), and percentage of roots in classes 0 thru 3 (those most likely to be harvested and taken to the factory). Percentages were transformed using arsin-square root to normalize the data for analyses. We had unusually high temperatures in the summer of 2000 which, combined with a high inoculum load, contributed to a severe root rot epidemic that progressed very quickly. Differences in DIs among entries were highly significant (P<0.001). Mean DIs across in the 2000 nursery for highly resistant FC705-1, resistant FC703, and highly susceptible FC901/C817 controls were 2.5, 2.7, and 4.4 respectively. Percentages of healthy roots were 16.0, 16.3, and 3.9% for these controls. Percentages of roots in disease classes 0 thru 3 were 79.9, 67.1, and 28.7 respectively. The highest and lowest DIs for the evaluated lines were 4.8 and 2.2 respectively. The resistant and highly resistant checks were developed and released in 1976 and 1983, respectively. A number of germplasm performed as well as these but none significantly better than FC705-1