Details for: PI 470093, Beta vulgaris L. subsp. vulgaris, 2423

Beta PIs from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2013

Thirty-one Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System (NPGS) Beta Collection [includes garden beet, sugarbeet, leaf beet, fodder beet (Beta vulgaris L), and wild beet (Beta spp.)] were evaluated for resistance to Cercospora beticola in an artificially produced epiphytotic environment (based on Ruppel, E.G. and J.O. Gaskill. 1971. J. Am. Soc. Sugar Beet Technol. 16:384). In 2013, all PIs examined were cultivated types (Beta vulgaris ssp. vulgaris). A randomized complete-block design, with three replications was used to evaluate germplasm at the Michigan State University Saginaw Valley Research and Extension Center (SVREC) near Frankenmuth, MI. The field had been planted in wheat in 2012. Internal controls included a moderately susceptible check, CE (kindly provided by Syngenta seeds), and a resistant check, EL50/2 (PI 664912). Single-row plots 4.5 m long, with 51 cm between rows were planted on 7 May 13. Azoxystrobin was applied in a 14 cm band in-furrow at planting to control Rhizoctonia damping-off and crown and root rot. The nursery was inoculated on 11 Jul with a liquid spore suspension (approximately 1 x 103 spores/ml as determined with a hemacytometer) of C. beticola. Inoculum was produced from a mixture of leaves collected from the 2012 inoculated leaf spot nursery at SVREC and naturally infected beets grown on the Michigan State University campus farms in East Lansing, MI. Visual evaluations of the plot with a disease index (DI) on a scale from where 0=no symptoms, 1=a few scattered spots, 2=spots coalescing or in large numbers on lower leaves only, 3= some dieback on lower leaves, but leaves not entirely dead, 4-8 are increasing amounts of dead and diseased tissue, 9= mostly dead with few remaining living leaves with large dead patches, and 10=all leaves dead. Evaluations were made on 16, 22, and 29 Aug, 5 and 12 Sep 13, with the peak of the epidemic occurring around 12 Sep. An evaluation was attempted subsequently, but several PIs were losing leaves following production of seed stalks and others were showing new leaf growth following defoliation from Cercospora leaf spot, so these ratings were not used. The field was sprayed once with ethofumesate on 9 May, three times with mixtures of phenmedipham, desmedipham, triflusulfuron methyl, and clopyralid (27 May, 8 Jun and 3 Jul 13), once with S-metolachlor (12 Jun 13) to control weed seedlings, and hand weeding was done as needed to control larger weeds. The beet crop was thinned by hand with the generous help of Michigan Sugar Cooperative. Bolting beets were removed throughout the season.

The high night temperatures in the summer of 2013, combined with high humidity and low rainfall, contributed to a moderate leaf spot epiphytotic. Supplemental moisture was applied using an overhead irrigation system 13, 16 and 17 Jul. The BeetCast leafspot advisory in the Frankenmuth area from 1 May to 20 Sep accumulated 185 daily severity values. Disease severity peaked by early Sep, after which regrowth started to outpace new disease development, so that disease ratings for several accessions remained constant or decreased after that rating, thus ratings are not given after this date. At the 12 Sep 13 rating, means of the resistant and susceptible internal controls for the entire nursery (including two additional experiments) were 3.1 and 5.2, respectively, across the nursery. At the peak of the epiphytotic in 2012 (12 Sep), these means were 3.1 and 5.0 for resistant and susceptible, respectively. Means of contributor lines in the entire nursery (including three additional tests) in 2013 ranged from 3.1 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. Nine accessions (Ames 2633, PI 467873, PI 467880, PI 46788, PI 527307, PI 558515, PI 590732, PI 614827 and PI 663212) 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, PI 590732, had average ratings significantly lower than the susceptible control at all rating dates. Three other accessions (Ames 2633, PI 467872, and PI 467881) had average ratings significantly lower than the susceptible control three of the four additional rating dates. In contrast, one accession, PI 470095, had average ratings that were significantly higher than the susceptible control at three of the five rating dates, and another accession, PI 505830, was significantly higher at two rating dates. Seven accessions (Ames 2632, PI 467872, PI 470089, PI 470096, PI 608797, PI 612768, and PI 612769) required removal of seed stalks from at least one replicate during the season. These data, and more information on the accessions evaluated, are available through the USDA-ARS GRIN database at .