Influence of Vesicular-Arbuscular Mycorrhizae on Phytophthora Root Rot of Three Crop Plants

Abstract

Citrus [Citrus sinensis cv. Pineapple], avocado [Persea americana ''Topa Topa''] and alfalfa [Medicago sativa ''Moapa 69''] seedlings, with or without endomycorrhizae formed by Glomus fasciculatus, were inoculated with P. parasitica, P. cinnamomi and P. megasperma, respectively. Little or no differences in response to the Phytophthora spp. 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 eperiments, 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. P concentrations in leaves of citrus and avocado seedlings infected with G. fasciculatus alone were significantly greater than concentrations in leaves of nonmycorrhizal seedlings. P concentrations in seedlings inoculated with both G. fasciculatus and Phytophthora, were similar to concentrations in nonmycorrhizal seedlings.