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United States Department of Agriculture

Agricultural Research Service

Research Project: Production Management Research For Horticultural Crops in the Gulf South

Location: Southern Horticultural Research

Title: Spread potential of binucleate Rhizoctonia from propagation floors to trays containing stem cuttings

Author
item Copes, Warren

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 13, 2013
Publication Date: June 1, 2013
Citation: Copes, W.E. 2013. Spread potential of binucleate Rhizoctonia from propagation floors to trays containing stem cuttings. Phytopathology. 103(Suppl.2):30. http://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-103-6-S2.1

Technical Abstract: Binucelate Rhizoctonia spp. (BNR), the cause of web blight, are present all year on container-grown azaleas in the southern U.S. BNR can be eliminated during vegetative propagation by submerging stem cuttings in 50°C water for 21 minutes. The objective was to evaluate risk of rooting trays being contaminated from inoculum on polypropylene fabric and gravel floors in propagation houses. Three experiments were done in 2011 and repeated in 2012. In experiment one, floors of commercial propagation houses were swab sampled on a grid pattern and sponges plated on Ko and Hora agar. 1-9% of 96 samples per cultivar were positive for BNR from fabric and gravel floors. In experiment two, samples of fabric and gravel inoculated with BNR were set under 70% shade and full sun, with and without interval timed irrigation, for six weeks. BNR recovery declined 75% under shade and 86-96% under full sun. In experiment three, trays with hot water treated azalea stem cuttings stuck in peat mixtures were set on or beside inoculated pieces of fabric and gravel and maintained under a misting regime for 12 weeks. In both years, BNR was not recovered from peat in trays of rooted stem cuttings even though BNR was recovered from 60-94% of the inoculated substrates at the end of 12 weeks. BNR persists on fabric and gravel floors but declines over the 6 weeks houses are empty. If floor surfaces are clean of organic matter, the risk of rooting trays becoming contaminated appear low.

Last Modified: 4/19/2014
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