Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 8, 2012
Publication Date: April 1, 2012
Citation: Hanson, L.E., Duckert, T.M., Goodwill, T.R., McGrath, J.M. 2012. Beta PIs from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2011. Plant Disease Management Reports. Available: http://www.plantmanagementnetwork.org/pub/trial/PDMR/reports/2012/FC037.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 7 and the disease was severe enough to start rating by mid August. Significant variability was detected between different entries. One of the PIs was not significantly different from the resistant control for disease severity on two of the three rating dates. A large number of the PIs produced seed stalks during the study and these had to be removed. Only six of the 30 PIs did not need to have seed stalks removed and one could not be rated past mid-August because most of the leaves died as the plants produced seed stalks, leaving too little tissue to rate.
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 May 5. The nursery was inoculated once with a liquid spore suspension of Cercospora beticola on July 7. 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 third date. By the fourth date, regrowth of several PIs was visible, and several PIs were dieing after having produced seed stalks, so ratings started to go down and were not recorded. At the third evaluation, means of the resistant and susceptible internal control were 3.5 and 5.9, respectively, across the nursery. In 2010, these means were 3.2 and 5.5, respectively. Means of the PIs ranged from 3.7 to 6.0. An analysis of variance on the disease indices determined that there were significant differences among entries (P=0.05) on all three dates of evaluation. One accessions was not significantly different from the resistant control at the first and third rating dates. Only six accessions and the two control varieites did not require removal of seed stalks during the course of the ratings.