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Importance of Chlamydospores as Primary Inoculum for Alternaria solani, Incitant of Collar Rot and Early Blight on Tomato. C. L. Patterson, Assistant Professor, Department of Plant Pathology, Oklahoma State University, WWAREC, P.O. Box 128, Lane 74555. Plant Dis. 75:274-278. Accepted for publication 10 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0274.

Chlamydospores were produced in hyphal and conidial cells of Alternaria solani on a basal salts agar medium and in infected tissues of several tomato cultivars. Conidia required desiccation as a prerequisite to chlamydospore transformation of cells. In contrast, chlamydospore production in hyphal cells was inhibited by desiccation. Collar rot developed on tomatoes grown in soil contaminated with chlamydospore inoculum or fresh hyphal cultures of the pathogen. Moreover, these inocula persisted in soil for 12 mo. Chlamydospores placed in depths of 0, 4, 8, and 12 cm in soil initiated infections and incited collar rot on tomato. A root rot developed when the inoculum was placed from 0 to 20 cm deep and chlamydospores were present in roots of plants infected by A. solani. Thus, chlamydospores were introduced into soil by tomato residue infected by A. solani, were responsible for long-term survival of the fungus, and, therefore, were the primary soilborne inocula for the pathogen.