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Interdependence of a Mite, Siteroptes reniformis, and a Fungus, Nigrospora oryzae, in the Nigrospora Lint Rot of Cotton. Franklin F. Laemmlen, Research Assistant, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Botany and Plant Pathology, Michigan State University, E. Lansing 48823; Dennis H. Hall, Extension Plant Pathologist, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 63:308-315. Accepted for publication 8 September 1972. DOI: 10.1094/Phyto-63-308.

The mite, Siteroptes reniformis, was consistently associated with Nigrospora lint rot of cotton bolls in California. Infection of bolls in the field averaged 23% when the soil at the base of plants was artificially infested with both Nigrospora oryzae and S. reniformis; 4%, when only N. oryzae was added to the soil; and 1%, when no inoculum of either was applied in the checks. When tubes containing N. oryzae and the mite, or N. oryzae alone, were attached to individual bolls, 99.2% and 15.1%, respectively, became infected. S. reniformis fed on N. oryzae mycelium, and young females had one to two spores of N. oryzae within their hysterosoma soon after exposure to the fungus. Infections developed in 91.6% of the locks inoculated with one-three mites carrying one spore each, whereas all locks were infected when inoculated with one-three mites carrying two spores each. S. reniformis required N. oryzae for normal growth and reproduction. The mite aids the fungus in dissemination, inoculation, and early growth. Temperature optima of N. oryzae (21-27 C) and S. reniformis (27 C) were similar. S. reniformis overwintered in diseased cotton locks. These data and observations indicate that S. reniformis serves as a vector of N. oryzae in the initiation of Nigrospora lint rot disease in California, and that a mutualistic form of symbiosis exists between them.

Additional keywords: symbiosis.