Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2011
Publication Date: March 28, 2011
Citation: Hanson, L.E., Duckert, T.M., Goodwill, T.R., McGrath, J.M. 2011. Beta PIs from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2010. Plant Disease Management Reports. 5:FC056. 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 1 and the disease was severe enough to start rating by the end of July. Significant variability was detected between different entries. Two entries had significantly lower average disease ratings than the susceptible control at early ratings, but by the end of the season these were not significantly different from the susceptible control. In contrast, two entries were observed that were particularly susceptible to the disease, with average disease ratings signficantly higher than the susceptible control at several rating times. A large number of the PIs produced seed stalks during the study and these had to be removed. Only 10 PIs did not need to have seed stalks removed.
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 commercial variety, 'CE', and a resistant variety, 'ACH 355'. The field was planted April 14. The nursery was inoculated once with a liquid spore suspension of Cercospora beticola on July 1. 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 between the fourth and fifth dates. After the fifth date, 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 3.2 and 5.5, respectively, across the nursery. In 2009, these means were 2.5 and 5.3, respectively. Means of the PIs ranged from 5.0 to 7.7. 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. Two accessions had average disease ratings significantly lower than the susceptible control at the second and third rating dates, but were not signficantly different from the susceptible control by the end of the rating period. In contrast, two accessions were observed that had significantly higher average disease ratings than the susceptible check on three of the five rating dates.