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Growth Characteristics of Several Isolates of Verticillium albo-atrum and Verticillium nigrescens from Cotton. T. D. Wyllie, Associate Professor, Department of Plant Pathology, University of Missouri, Columbia 65201; J. E. DeVay, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 60:907-910. Accepted for publication 17 January 1970. DOI: 10.1094/Phyto-60-907.

Per cent germination of conidia, rate of sporulation, and the effect of C : N ratios on microsclerotial and chlamydospore formation was determined for cotton plant defoliating (T9) and nondefoliating (SS4) isolates of Verticillium albo-atrum and V. nigrescens (isolate 68). T9 conidia germinated more rapidly than conidia of SS4 at temp of 21, 24, 27, and 30 C. Conidia of SS4, however, failed to germinate at 33 C while those of T9 and 68 did germinate. Sporulation rates of T9 and 68 were twice that of SS4 after 80-hr incubation in vitro. Furthermore, T9 was capable of producing microsclerotia over a wider range of carbon : nitrogen ratios than isolate SS4. These data suggest that other factors as well as increased virulence may account for the increased prevalence of the defoliating strain T9 in California.