VIEW ARTICLE

Ecology and Epidemiology

Survival of Verticillium albo-atrum on Nonsuscept Roots and Residues in Field Soil. D. M. Benson, Department of Plant Pathology, University of California, Berkeley 94720, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27607; L. J. Ashworth, Jr., Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 66:883-887. Accepted for publication 23 January 1976. DOI: 10.1094/Phyto-66-883.

Parasitic colonization of barley roots by Verticillium albo-atrum (microsclerotial type), the cotton wilt pathogen, was not a significant survival mechanism under field conditions. Although up to 5.6 colonies per 100 cm of barley root were recorded by plating on selective media during the growing season, 1 to 6 months after harvest buried root residues of immune crops such as alfalfa, barley, corn, and sorghum did not contain V. albo-atrum microsclerotia. Barley and cotton stems were not colonized after incubation periods of 1 to 9 weeks in naturally infested soil. No difference was found in inoculum density of V. albo-atrum during the growing season in rhizosphere (RS) or nonrhizosphere field soil (NRS) from alfalfa, barley, corn, and sorghum. Few V. albo-atrum colonies were recovered from nonsuscept rhizoplanes following a 72-hour air drying period. Nonsuscept rhizosphere and rhizoplane isolates of V. albo-atrum were pathogenic to cotton. Symptoms of Verticillium wilt never were observed on nonsuscepts growing under field conditions, nor was the fungus isolated from plant tissue above soil line.