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Differential Effects of the Defoliating and Nondefoliating Pathotypes of Verticillium dahliae Upon the Growth and Development of Gossypium hirsutum. G. E. Friebertshauser, Research assistant, Department of Plant Pathology, University of California, Davis 95616; J. E. DeVay, professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 72:872-877. Accepted for publication 7 December 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-872.

The effect of time of inoculation with either the defoliating (T9) or nondefoliating (SS4) pathotypes of Verticillium dahliae Kleb. upon the growth and development of upland cotton (Gossypium hirsutum, cultivar Acala SJ-2) was studied in the San Joaquin Valley of California in 1977 and 1978. Approximately 2,000 plants were stem-puncture inoculated at three different stages of growth in a 0.9-hectare field plot. Plant growth analysis in terms of plant heights, number of main stem nodes, squares, and bolls was made weekly throughout the growing season. In addition, fresh and dry weights of plant components were determined for biomass analysis. Data were also collected on the effect of the pathotypes upon seed cotton yields and fiber quality. Reduction of leaf dry matter accumulation was the plant component most affected by inoculation with V. dahliae. The defoliating pathotype had greater effects upon plant growth and development and seed cotton yields at all inoculation times than did the nondefoliating pathotype. Cotton plants inoculated with either pathotype of V. dahliae compensated for reduced photosynthate supply by reduction of fruiting load characteristic of uninfected plants under stress conditions.

Additional keywords: pathobiology, plant growth analysis.