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The Effects of a Mycoparasite on the Mycorrhizal Fungus, Glomus deserticola. T. C. Paulitz, Graduate student, Department of Plant Pathology, University of California, Riverside 92521, Present address: Dept. of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523; J. A. Menge, professor, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 76:351-354. Accepted for publication 2 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-351.

In vitro experiments have shown Anguillospora pseudolongissima to be a mycoparasite of vesicular-arbuscular mycorrhizal fungus spores. The mycoparasite was added to a low-phosphorus sandy loam containing 10-1, 10-2, and 10-3 serial dilutions of inoculum of the mycorrhizal fungus, Glomus deserticola. Onion seeds were planted in the soil-inoculum mixture after a 2-wk incubation period. A. pseudolongissima significantly reduced root colonization by G. deserticola and growth response of onions after 80 days in treatments where the mycorrhizal inoculum was diluted to 10-3 of the original inoculum. No significant differences were seen between mycoparasite and nonmycoparasite treatments containing mycorrhizal fungus inoculum diluted 10-1 and 10-2 times. Most-probable-number calculations showed that A. pseudolongissima reduced the initial effective propagule density of the mycorrhizal fungus over 50%. Under conditions of low inoculum density of the mycorrhizal fungus and low phosphorus availability, a mycoparasite can indirectly reduce plant dry weight by adversely affecting the fungal mycorrhizal symbiont.

Additional keywords: Allium cepa, hyperparasite.