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Temperature Effects upon Development and Pathogenicity of Defoliating and Nondefoliating Pathotypes of Verticillium dahliae in Leaves of Cotton Plants. Susan H. Temple, Department of Plant Pathology, University of California, Davis 95616; J. E. DeVay(2), and Linda L. Forrester(3). (2)(3)Department of Plant Pathology, University of California, Davis 95616. Phytopathology 63:953-958. Accepted for publication 4 February 1973. DOI: 10.1094/Phyto-63-953.

Development of symptoms of Verticillium wilt involving chlorosis and necrosis of leaves of cotton (Gossypium hirsutum) is preceded by invasion of leaf tissues by Verticillium dahliae, the plugging of xylem elements with a gel-like substance, and the wilting of limited leaf areas. At approximately 23 C, the pathogen was located mainly in xylem elements and xylem parenchma and was found generally throughout infected leaves of stem-inoculated plants. The pathogen was always isolated from leaf areas with symptoms of Verticillium wilt and usually from symptomless areas of the leaves. The defoliating pathotype (T9) of V. dahliae was isolated from all sections of petioles within 48 hr of stem inoculation, whereas the nondefoliating pathotype (SS4) was not isolated consistently from all sections of petioles until the 4th day; by the 10th day both pathotypes were recovered from all sections of infected leaves. Resistance of cotton to Verticillium wilt at 33 C (day temperature) was due mainly to the inhibition and death of V. dahliae in foliar tissues. In infected leaves the defoliating pathotype was better able to withstand high air temperature compared with the nondefoliating pathotype which could not be recovered from leaves after 16 days.

Additional keywords: defoliation, water stress, wilting, rate of infection, Gossypium hirsutum.