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Symptomatology and Formation of Microsclerotia in Weeds Inoculated with Verticillium dahliae from Cotton. William M. Johnson, Assistant professor, Langston University Research Program, Langston University, Langston, OK 73050; E. K. Johnson(2), and L. A. Brinkerhoff(3). (2)Associate professor, Department of biology, Langston University, Langston; (3)Professor emeritus, Department of Plant Pathology, Oklahoma State University, Stillwater, 74074. Phytopathology 70:31-35. Accepted for publication 2 July 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-31.

Symptomatology and microsclerotial formation were evaluated among 35 weed species inoculated with a defoliating strain of Verticillium dahliae isolated from upland cotton. The weed species are of economic importance in cotton production. A wide range of disease reactions was observed (0.04.4 on a 05 scale). Of 35 species, 19 were infected systemically. In four of the 35, V. dahliae was isolated from the proximal region of taproots with no vascular discoloration evident in basal stem areas. Twelve species were highly resistant to the wilt pathogen. Some infected weeds failed to exhibit any external symptoms, but stem tissues had mild to extensive vascular discoloration. The virulence of V. dahliae isolates recovered from inoculated weeds varied, but most isolates induced moderate to severe symptoms in susceptible cotton. Development of microsclerotia in senescent tissues of infected weeds could be an important factor in the failure of rotation programs to control the pathogen effectively. This study indicates that weeds can serve as a source of microsclerotia. The data support the need for an effective weed control program as an aid in reducing the incidence of Verticillium wilt.

Additional keywords: crop rotation, Gossypium hirsutum, pest interactions.