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Interaction of the Endomycorrhizal Fungus Gigaspora margarita and Root-Knot Nematode on Cotton. R. W. Roncadori, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602; R. S. Hussey, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens, GA 30602. Phytopathology 67:1507-1511. Accepted for publication 16 June 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1507.

Inoculation of cotton (Gossypium hirsutum ‘McNair 511’ and ‘Stoneville 213’) with azygospores of Gigaspora margarita significantly increased vegetative growth and square production (flower bud initials and flowers) over nonmycorrhizal plants in greenhouse studies. Growth stimulation and plant development were greater at a low fertility rate (250 μg/g 10-10-10 NPK) than at a high fertility level (500 μg/g). Shoot weight and square production were reduced by Meloidogyne incognita in the nematode-susceptible Stoneville 213 cultivar, but not in the resistant McNair 511 cultivar. In joint inoculations with the endophyte and M. incognita, development of endomycorrhizae nullified the stunting caused by the nematode. Mycorrhizal stimulation of plant development, however, was affected little by root-knot nematode activities. Azygospore production was greatest in joint culture on McNair 511 at the high fertility rate and on Stoneville 213 at the low fertility level. Nematode egg production per gram of root was not affected by G. margarita, but total eggs per plant was increased on mycorrhizal Stoneville 213 since their root systems were considerably larger than those of the controls.

Additional keywords: Gossypium hirsutum, Meloidogyne incognita.