Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 2011
Publication Date: March 30, 2009
Citation: Hanson, L.E., Duckert, T.M., McGrath, J.M. 2009. Beta PIs from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2008. Plant Disease Management Reports. The American Phytopathological Society. 3:V017. DOI: 10.1094/PDMR01. Available: http://www.plantmanagementnetwork.org/pub/trial/PDMR/reports/2009/V017.pdf. Interpretive Summary: Cercospora leaf spot is one of the most widespread and destructive fungal disease of beet and occurs wherever beets are grown. Host resistance is an important tool for managing the disease, caused by the fungus Cercospora beticola. In an ongoing effort to find sources of resistance to Cercospora, 61 Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System were tested for resistance to the leaf-spotting fungus, C. beticola. The disease reached moderate levels in late August. Significant variability was detected between different entries. One accession was not significantly different for disease rating from the resistant control at all rating dates. An additional five accessions had significantly lower disease ratings than the susceptible control for at least three of the 5 rating periods. The identification of potential resistance in PIs may allow for new sources of resistance to be used by breeders and a chance to eventually expand the genetic pool available for use to the sugar beet and vegetable beet communities.
Technical Abstract: Sixty-two Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System were evaluated in an artificially produced epiphytotic for resistance to Cercospora beticola at the Saginaw Valley Bean and Beet Research Farm in MI. Internal controls included a susceptible check, USH20, and a resistant check, ACH 355. The nursery was inoculated with a liquid suspension of Cercospora beticola. Visual evaluations on the plot, producing a disease index (DI) on a scale from 0 (no disease) to 10 (plant dead), were made on five dates, with the peak of the epidemic occurring on or after the fourth date. At our fourth evaluation, means of the resistant and susceptible internal control were 2.4 and 5.2, respectively, across the nursery. In 2007, these means were 1.8 and 5.3, respectively. Means of the PIs ranged from 3.3 to 6.3. An analysis of variance on the disease indices determined that there were significant differences among entries (P=0.05) on all five dates of evaluation. One accession was not significantly different from the resistant control at all five ratings. Three accessions had disease severity ratings significantly lower than the susceptible control on at least three rating dates.