APS Abstracts of Presentations

Growth chamber assay for Phymatotrichum root rot of Medicago species
Presenter: H.-K. Lee, The Samuel Roberts Noble Foundation, Inc., Forage Improvement Division, 2510 Sam Noble Parkway, Ardmore, OK 73401
Co-Author(s): S. Marek, Oklahoma State University, Department of Entomology & Plant Pathology, 127 Noble Research Center, OSU, Stillwater, OK 74078; M. Sledge, The Samuel Roberts Noble Foundation, Inc., Forage Improvement Division, 2510 Sam Noble Parkway, Ardmore, OK 73401
Phytopathology 95:1112

Alfalfa (Medicago sativa L.) is the most important forage legume in the world, producing both high quality hay and pastures. In Oklahoma, alfalfa is produced on approximately 400,000 acres and generates more than $100 million. Phymatotrichum root rot (=“cotton root rot” or “Texas root rot”) is one of the most important diseases of alfalfa in Oklahoma and is caused by soil-borne fungus, Phymatotrichopsis omnivora (Duggar) Hennebert. A growth chamber screening procedure was developed to assay Medicago germplasm for resistance to Phymatotrichum root rot. Twenty alfalfa cultivars and one clover cultivar were planted in 20-row seeder trays containing sterilized commercial peat mix and trays were maintained in growth chambers at 22–28°C. Strains of P. omnivora isolated from cotton (Austwell, TX) and alfalfa (Courtney, OK) were cultured on sterilized sorghum grains and 20 g used to inoculate each row of the tray. Ten days after inoculation, alfalfa leaves became chlorotic and bronzed and roots displayed necrotic lesions and signs of pathogen. Several potential resistant Medicago germplasms were identified for further field study.

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