Beta Plant Introductions from the USDA-ARS NPGS evaluated for resistance to Cercospora beticola, 2014

摘要

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.)] 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). 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 2013. 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 5 May. Moncut 70DF (flutolonil) was applied at 0.0091 kg/100 m row in a 14 cm band in-furrow at planting to control Rhizoctonia damping-off and Quadris 2.08SC (azoxystrobin) was applied at 0.0067 L/100 m row on 5 Jun-to manage Rhizoctonia crown and root rot with limited potential to impact leaf spot development. The nursery was spray-inoculated on 10 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 2013 inoculated leaf spot nursery at SVREC and naturally infected beets grown on the Michigan StateUniversity 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 14, 21, and 28 Aug, and 3 Sep, withthe peak of the epidemic occurring around 3 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, sothese ratings were not used. Weeds were controlled three times with mixtures of phenmedipham, desmedipham, triflusulfuron methyl, and clopyralid (1, 16, and 28 Jun) and once with S-metolachlor (28 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.