Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2013
Publication Date: March 26, 2013
Citation: Hanson, L.E., Goodwill, T.R., McGrath, J.M. 2013. Beta PIs from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2012. Plant Disease Management Reports. Available: http://www.plantmanagementnetwork.org/pub/trial/pdmr/reports/2013/FC067.pdf. Interpretive Summary: Cercospora leaf spot is one of the most widespread and destructive fungal disease of beet and occurs wherever beets are grown. One important method of managing the disease is the use of varieties with resistance to the pathogen, Cercospora beticola. In an ongoing effort to find sources of resistance to Cercospora, 30 Plant Introdcutions (PIs) from the USDA-ARS National Plant Germplasm System were tested for their response to the leaf-spotting fungus, Cercospora beticola. Plants were inoculated July 11. Because of drought conditions, supplement irrigation was used and the disease was severe enough to start rating by the end of August. Significant variability was detected between different entries. One entry showed a similar level of resistance as the resistant control at all rating dates, and a second showed a similar level late in the season. Three entries had more severe disease than the susceptible control. Twelve of the PIs produced seed stalks during the study and these had to be removed. Both of the potential resistant entries were in this group. Results from the continuing survey have the potential to identify new sources of resistance to this important disease.
Technical Abstract: Thirty Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System were evaluated for resistance to Cercospora beticola in an artificially produced epiphytotic at the Saginaw Valley Research and Extension Center near Frankenmuth, MI. Internal controls included a susceptible germplasm, C869, and a resistant germplasm, EL50/2. The field was planted May 10. The nursery was inoculated once with a liquid spore suspension of Cercospora beticola on July 11. Visual evaluations on the plot, producing a disease index (DI) on a scale from 0 (no disease) to 10 (plant dead), were made on four dates, with the peak of the epidemic occurring around the fourth date. After the fourth rating regrowth of several PIs was visible, so ratings started to go down. At our fourth evaluation, means of the resistant and susceptible internal control were 3.1 and 5.0, respectively, across the nursery. In 2011, these means were 3.5 and 5.9, respectively. Means of the PIs ranged from 3.0 to 7.3. An analysis of variance on the disease indices determined that there were significant differences among entries (P=0.05) on all four dates of evaluation. One accession had average disease ratings that were not signficantly different from the resistant control at all ratings and a seccond accession was not significantly different at the final two rating dates. In contrast, two accessions had average disease severity ratings that were significantly higher than the susceptible control at three of the four rating dates and a third was significantly higher at the last two ratings. Twelve accessions required removal of seed stalks during the season, indicating a potential for an annual growth habit in the Michigan growing region. This included both the potentially resistant accessions.