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Characteristics and Concentration of Propagules of Verticillium dahliae in Air-Dried Field Soils in Relation to the Prevalence of Verticillium Wilt in Cotton. J. E. DeVay, Department of Plant Pathology, University of California, Davis 95616; Linda L. Forrester(2), R. H. Garber(3), and E. J. Butterfield(4). (2)(3)(4)USDA Cotton Experiment Station, Shafter, California 93263. Phytopathology 64:22-29. Accepted for publication 15 June 1973. DOI: 10.1094/Phyto-64-22.

Viable microsclerotia of Verticillium dahliae were recovered from field soils that had been air-dried for at least 6 wk. These microsclerotia, ranging from 11 to 225 µ in widest dimension, consisted of clusters of hyaline cells (7-8 µ in diam) with thickened walls which were colorless to slightly pigmented. After 6 hr in a favorable environment, microsclerotia began to germinate, commonly producing up to 36 germ hyphae and several sporophores with verticillate branches and conidia. The correlation coefficient (r=-0.139) for the relationship between the concn of microsclerotia in air-dry soil samples from different fields and percentage of diseased plants (foliar symptoms) was not significantly different from zero; similarly, the relationship involving samples from a single field was again nonsignificant (r=0.175). These data indicate that the concn of microsclerotia in air-dry field soil is probably not the limiting factor in disease development.

Additional keywords: inoculum density, soil plating, epidemiology.