Details for: PI 515964, Beta vulgaris L. subsp. vulgaris, C790

Beta Plant Introductions from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2015.

Thirty 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.)] along with seven entries resulting from crossing of previous years (2008-2013) PIs selected from Cercospora leaf spot tests (Hanson, et al. PDMR 3:V017, 6:FC037, 7:FC067. 8:FC170) with East Lansing germplasm and USDA-ARS release SR102 (PI 675153) were evaluated for resistance to Cercospora beticola in an artificially produced epiphytotic environment (based generally on Ruppel, E.G. and J.O. Gaskill. 1971. J. Am. Soc. Sugar Beet Technol. 16:384). Previous year’s PIs were selected for their general levels of agronomic performance (e.g. emergence, stand persistence, and seed production) to augment genetic diversity in the cultivated germplasm pool and not specifically for Cercospora leaf spot performance. 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 with clover underseeded in 2014. Internal controls included a susceptible check, 12N0050 (kindly provided by L. Campbell), and a resistant check, EL50/2 (PI 664912). Single-row plots 4.5 m long, with 51 cm between rows were planted on 30 Apr. Quadris 2.08SC (azoxystrobin) was applied at 0.0091 kg/100 m row in a 14 cm band in-furrow at planting to control Rhizoctonia damping-off. The nursery was spray-inoculated on 2 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 2014 inoculated leaf spot nursery at SVREC and naturally infected beets grown at SVREC and 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 0-10 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 13, 20, and 27 Aug, and 3 and 9 Sep, with the peak of the epidemic occurring around 9 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. Weeds were controlled by a preplant application of ethofumesate 7 May, three times with mixtures of phenmedipham, desmedipham, triflusulfuron methyl, and clopyralid (23 May and 11, and 24 Jun) and once with S-metolachlor (17 Jun). 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 moderate night temperatures in the summer of 2015, combined with high humidity and rainfall, contributed to a moderate leaf spot epiphytotic. Supplemental moisture was applied using an overhead irrigation system 3, 6 and 10 Jul. The BeetCast leafspot advisory in the Frankenmuth area from 1 May to 20 Sep accumulated 224 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 were not given after this date. At the 9 Sep 15 rating, means of the resistant and susceptible internal controls for the entire nursery (including two additional experiments) were 3.2 and 7.0, respectively, across the nursery. At the peak of the epiphytotic in 2014 (3 Sep), these means were 2.4 and 5.8 for resistant and susceptible checks, respectively. Means of contributor lines in the entire nursery (including three additional tests) in 2015 ranged from 2.7 to 7.0. 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. All accessions were significantly different from the resistant control at the final four rating dates, but three accessions, PIs 506218, 515965, and 518167, as well as the East Lansing breeding materials EL- A027162 and EL-A029709 were not significantly different from the resistant control at the first rating date. At the final rating date, near the peak of the epiphytototic, eleven accessions (in order from lowest to highest disease severity rating: PI 518167, PI 538250, PI506238, PI 518314, NSL 176410, NSL183446, PI296541, NSL28041, NSL183461, PI357367, and PI505828) and the East Lansing breeding lines were significantly different from the susceptible control . Only two accessions (NSL34020 and PI518314) required removal of seed stalks from at least one replicate during the season while five of the crosses from previous years PIs required such removal (735, 779, 780, 791, and 795). These data, and more information on the accessions evaluated, are available through the USDA-ARS GRIN database at .