VIEW ARTICLE

Ecology and Epidemiology

Influence of Vesicular-Arbuscular Mycorrhizae on Phytophthora Root Rot of Three Crop Plants. R. M. Davis, Graduate research assistant, Department of Plant Pathology, University of California, Riverside, CA 92521; J. A. Menge(2), and G. A. Zentmyer(3). (2)(3)Assistant professor, and Professor, respectively, Department of Plant Pathology, University of California, Riverside, CA 92521. Phytopathology 68:1614-1617. Accepted for publication 8 June 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1614.

Citrus, avocado, and alfalfa seedlings, with or without endomycorrhizae formed by Glomus fasciculatus, were inoculated with Phytophthora parasitica, P. cinnamomi, and P. megasperma, respectively. Little or no differences in response to the Phytophthora species were observed between mycorrhizal and nonmycorrhizal citrus or alfalfa seedlings, but mycorrhizal avocado seedlings were affected more severely by P. cinnamomi than were nonmycorrhizal avocado seedlings. In the citrus and avocado experiments, the growth stimulus caused by the mycorrhizal fungus was eliminated when Phytophthora was present. Sporulation by G. fasciculatus on citrus was affected adversely by P. parasitica. Phosphorus concentrations in leaves of citrus and avocado seedlings infected with G. fasciculatus alone were significantly greater than concentrations in leaves of nonmycorrhizal seedlings. Phosphorus concentrations in seedlings inoculated with both G. fasciculatus and Phytophthora, however, were similar to concentrations in nonmycorrhizal seedlings.