IMPACT ON ARBUSCULAR MYCORRHIZA FORMATION OF PSEUDOMONAS STRAINS USEDAS INOCULANTS FOR BIOCONTROL OF SOIL-BORNE FUNGAL PLANT-PATHOGENS

The arbuscular mycorrhizal symbiosis, a keg component of agroecosystem s, was assayed as a rhizosphere biosensor for evaluation of the impact of certain antifungal Pseudomonas inoculants used to control soil-bor ne plant pathogens. The following three Pseudomonas strains mere teste d: wild-type strain F113, which produces the antifungal compound 2,4-d iacetylphloroglucinol (DAPG); strain F113G22, a DAPG-negative mutant o f F113; and strain F113(pCU203), a DAPG overproducer. Wild-type strain F113 and mutant strain F113G22 stimulated both mycelial development f rom Glomus mosseae spores germinating in soil and tomato root coloniza tion. Strain F113(pCU203) did not adversely affect G. mosseae performa nce. Mycelial development, but not spore germination, is sensitive to 10 mu M DAPG, a concentration that might he present in the rhizosphere . The results of scanning electron and confocal microscopy demonstrate d that strain F113 and its derivatives adhered to G. mosseae spores in dependent of the ability to produce DAPG.