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Effect of Pythium irregulare on Cotton Growth and Yield, and Joint Action with Other Soil-Borne Pathogens. R. W. Roncadori, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30602; P. S. Lehman(2), and S. M. McCarter(3). (2)(3)Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30602. Phytopathology 64:1303-1306. Accepted for publication 8 May 1974. DOI: 10.1094/Phyto-64-1303.

In field experiments, certain symptoms of Pythium root rot of cotton, primarily an early-season disease, persisted throughout much of the growing season. Seed cotton yield of plants infected with P. irregulare was 11-14% less than that of the controls. However, height growth was only retarded for 2-3 mo after transplanting, and differences were not evident at harvest. In greenhouse studies, Pythium-infected and check plants were transplanted into fumigated and nonfumigated soils, which had been collected from three different field locations in Georgia. Soil from two of the sites contained mixtures of plant parasitic nematodes; that from the third site was infested with root knot nematode and the Fusarium wilt fungus. In all fumigated soils, reduced shoot growth caused by Pythium root rot was evident only 75-90 days after transplanting, and final root growth and boll production were only slightly decreased. Check transplants grew vegetatively and fruited better in fumigated than in nonfumigated soils, indicating the harmful activity of certain native soil-borne pathogens. The growth of infected transplants in one nonfumigated field soil sample suggested the action of a nematode-Pythium root rot complex. Both shoot growth and boll production were reduced to a greater degree by joint pathogen activity, than when either the nematodes or fungus attacked individually, suggesting an additive effect.

Additional keywords: Gossypium hirsutum, nematodes, Fusarium wilt.