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Disease Note.

First Report of Rhizoclonia sp. CAG-5 on cotton in Georgia. R. E. Baird, RDC, P.O. Box 1209; Plant Pathology Department, Tifton, GA 31794.. T. B. Brenneman and D. K. Bell, CPES, Plant Pathology Department, Tifton, GA 31794. Plant Dis. 79:320. Accepted for publication 2 February 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0320E.

In a field infested with root-knot (Meloidogyne incognita (Kofoid and White) Chilwood located near Tifton, GA, cotton (Gossypium hirsutum L.) plants grown in a peanut rotation study were stunted or dying within plots planted continuously to cotton. Isolations from root systems of healthy and damaged cotton plants in these plots resulted in the recovery of many different fungi, including three Fusarium Spp., Rhizoctonia solani AG-4 and the binucleate Rhizoclonia sp. CAG-5. Previously, CAG-5 was reported to be pathogenic on Cucumis spp. in Georgia. The CAG-5 isolate B1-15S was tested in the greenhouse for pathogenicity by mixing 50 ml of cornmeal sand inoculum (3 g cornmeal, 100 g sand, and 20 ml of distilled water) into six pots per isolate containing 2.0 L of sterile soil per pot (20 100 cm). Six pots containing noninfested soil were also included. Six nonfungicide-treated cotton seeds (cv. Georgia King) were sown into each pot. Plant stands averaged three plants per pot for the BI-15S treatment, four for the AG-4 isolate treatment, and five to six for the noninfested treatment. When the roots were evaluated for disease severity, lesions were observed at the base of the lower stems and roots in the pots infested with BI-15S. The AG-4 isolate was less damaging than the binucleate Rhizoclonia isolates. The two pathogens were reisolated from the lesion tissue. When the experiment was repeated, similiar results occurred The role of M. incognita on disease severity by CAG-5 is unclear and further studies are warranted.