Details for: PI 518402, Beta vulgaris L. subsp. maritima (L.) Arcang., WB 724

Sixty one Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System (NPGS) (Garden Beet, Sugar Beet, Leaf Beet, Fodder Beet, and wild beet) were evaluated in an artificially produced epiphytotic environment (Ruppel, E.G., and J.O. Gaskill. 1971. Techniques for evaluating sugarbeet for resistance to Cercospora beticola in the field. J. Am. Soc. Sugar Beet Technol. 16:384-389) at the Saginaw Valley Bean and Beet Research Farm (B&B) in MI. A randomized complete-block design, with three replications was used to evaluate germplasm. Internal controls included a susceptible check, variety USH20, and a resistant check, ACH355. One-row plots m long, with 56 cm between rows were planted on 1 May 08. Azoxystrobin was applied in a band in furrow at planting and broadcast on 16 Jun 08 to control Rhizoctonia damping-off and root rot. The nursery was inoculated on 10 Jul 08 with a liquid spore suspension. Visual evaluations on the plot with a disease index (DI) on a scale from 0 (no disease) to 10 (plant dead) at the B&B were made on 5 Aug, 12 Aug, 19 Aug, 26 Aug, 2 Sep and 9 Sep 08, with the peak of the epidemic occurring around 2 Sep 08. The field was sprayed four times with phenmedipham, desmedipham, triflusulfuron methyl, and clopyralid (9 and 20 May and 2 and 12 Jun 08) and a cultivation was performed on 7 July 08 to control weeds. The field was thinned by hand. Bolting beets were removed 1 Sep 08, after which some annual materials could not be rated as there was not sufficient remaining tissue.

The moderate nighttime temperatures in the summer of 2008, combined with good moisture, contributed to a moderate leaf spot epidemic. Disease severity peaked by early September, after which regrowth started to outpace new disease development, so that disease ratings remained constant or decreased after that rating (trial mean 9 Sep 08 = 4.2), thus ratings are not given after this date. At our 2 Sep 08 rating means of the resistant and susceptible internal control for the entire nursery (including three additional experiments) were 2.4 and 5.2 (scale of 0-10), respectively, across the nursery. In 2007 (27 Sep), these means were 1.8 and 5.3, respectively. Means of contributor lines in the entire nursery (including five additional tests) in 2008 ranged from 2.3 to 6.8. An analysis of variance (PROC GLM - SAS) on the disease indices (visual evaluation scores) determined that there were significant differences among entries (P#0.05) on all dates of evaluation. One accession (PI540576) had ratings that were not significantly different from the resistant control at all rating dates. Five accessions (PI518309, PI504261, PI540612, PI518371, and PI540600) had disease ratings that were significantly lower than the susceptible control on at least three of the last rating dates. These data, and more information on the accessions evaluated, are available through the USDA-ARS GRIN database at http://www.ars-grin.gov/npgs.