The pathogenicity of Verticillium albo-atrum as affected by muck soil antagonists.

There are few reports of the application of antibiosis as a possible means of controlling Verticillium alboatrum Reinke and Berthold. Most of these publications are concerned with in vitro studies which report the effects of various organisms or their products on V. albo-atrum (Ark and Hunt, 1941; Arnstein et al., 1948; Smith, 1947). Wilhelm (1951a) effected a reduction in the inoculum potential of V. albo-atrum by amending pots of field-infested soil with blood meal, fish meal, cottonseed meal, and ammonium sulfate. In other studies, Wilhelm (1951b) reported: (1) that V. alboatrum was unable to colonize 3 natural soils after a period of 6 weeks following the introduction of Verticillium into the soils in the form of spores or sclerotia on sterilized pieces of tomato stem; (2) observations that this pathogen grows readily in sterilized soil; (3) on the effects of introducing isolated species of soil fungi singly into pots simultaneously with V. alboatrum. In the last case this author found that species of Gliocladium, Chaetomium, Stachybotrys, and Myrothecium killed or checked the growth of Verticillium. It has been noted for some time by the research workers at Purdue University investigating the Verticillium wilt of peppermint (Johnson, 1951; Luck, 1953) that this fungus will readily colonize sterilized muck soil but can not be isolated from unsterilized muck soil. This fact has suggested that it is biologically reduced in the soil. The purpose of this study was to determine the effectiveness of certain fungi in controlling V. alboatrum, and then ascertain the persistence of their antibiotic products in muck soil, as well as their in vivo effect upon the pathogenicity of this organism.