Location: Sugarbeet and Bean Research
Title: Beta PIs from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2013 Authors
Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 27, 2014
Publication Date: N/A
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, 31 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 and the disease was severe enough to start rating by mid August. Significant variability was detected between different entries. Nine entries were not significantly different from the resistant control at the first rating (August 16), but all evaluated PIs had significiantly higher ratings than the resistant control at all other rating dates. One PI had average disease severity ratings significantly lower than the susceptible control at all rating dates and three PIs had ratings significantly lower than the susceptible control at three of the four ratings after the first. In contrast, one entry were observed that was particularly susceptible to the disease, with average disease ratings signficantly higher than the susceptible control at three of the five ratings. Seven of the PIs produced seed stalks during the study and these had to be removed. Materials identified in these screenings may be useful sources for resistance breeding.
Technical Abstract: Thirty-one 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, Michigan. Internal controls included a susceptible variety, 'CE', and a resistant germplasm 'EL50/2'. The field was planted May 7. 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 completely defoliated), were made on five dates, with the peak of the epidemic occurring around the fifth date. After the fifth date, regrowth of several PIs was visible, so ratings started to go down. At our fifth evaluation, means of the resistant and susceptible internal control were 3.1 and 5.2, respectively, across the nursery. In 2012, these means were 3.1 and 5.0, respectively. Means of the PIs ranged from 4.0 to 6.7. 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. Nine accessions were not significantly different from the resistant control at the first rating, but all were significantly different from the resistant control at all other rating dates. One of these accessions had average ratings significantly lower than the susceptible control at all rating dates. Three other accessions had average ratings significantly lower than the susceptible control three of the four additional rating dates. In contrast, one accession had average ratings that were significantly higher than the susceptible control three of the five rating dates, and another accession was significantly higher at two rating dates. Seven accessions required removal of seed stalks from at least one replicate during the season