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Potential of Using Culture Filtrates from Verticillium albo-atrum to Evaluate Alfalfa Germ Plasm for Resistance to Verticillium Wilt. Karen F. Ireland, Former Graduate Student, Department of Plant Pathology, Pennsylvania State University. K. T. Leath, Research Plant Pathologist, U.S. Regional Pasture Research Laboratory, University Park, PA 16802. Plant Dis. 71:900-903. Accepted for publication 1 June 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/PD-71-0900.

The potential was assessed for using cellfree filtrates from potato-dextrose broth cultures of Verticillium albo-atrum in a fast, effective screening procedure for Verticillium wilt resistance in alfalfa. In one assay, cut stems were allowed to imbibe filtrate and were rated for symptoms 7 days later. The symptoms that developed in susceptible cuttings after this treatment were typical of those in field-infected alfalfa. Six percent of the cuttings from susceptible Saranac were rated resistant by this procedure, compared with 32 and 56% from resistant Maris Kabul and NAPB-34, respectively. Control cuttings treated with uninoculated potato-dextrose broth or autoclaved water did not develop symptoms. Similar results were obtained with susceptible cuttings after uptake of filtrate from V. albo-atrum cultured in alfalfa decoction medium. In the second assay. filtrate was perfused by pressure into the leaflets. Susceptible leaflets became chlorotic after 46 days. Seventeen percent of Saranac and 70% of NAPB-34 plants were rated resistant by this method. Control treatments of uninoculated culture medium or autoclaved water did not cause symptoms. The activity of the filtrate remained stable after autoclaving or freezing.

Keyword(s): disease resistance, lucerne, Medicago sativa.