RESPONSE OF SPRING WHEAT (TRITICUM-AESTIVUM) TO INTERACTIONS BETWEEN PSEUDOMONAS SPECIES AND GLOMUS-CLARUM NT4

The effects of interactions between pseudomonads (Pseudomonas cepacia strains R55 and R85, P. aeruginosa strain R80, P. fluorescens strain R 92, and P. putida strain R104) and the arbuscular mycorrhizal fungus G lomus clarum (Nicol. and Schenck) isolate NT4, on spring wheat (Tritic um aestivum L. cv. Laura), grown under gnotobiotic and nonsterile cond itions, were investigated. Although plant growth responses varied, pos itive responses to pseudomonad inoculants generally were obtained unde r gnotobiotic conditions. Shoot dry weight enhancement ranged from 16 to 48%, whereas root enhancement ranged from 82 to 137%. Shoot growth in nonsterile soil, however, was unaffected by pseudomonad inoculants, or reduced by as much as 24%. Shoot growth was unaffected or depresse d by G. clarum NT4 whereas early root growth was enhanced by 38%. Sign ificant interactions between the pseudomonad inoculants and G. clarum NT4 were detected. Typically, dual inoculation influenced the magnitud e of response associated with any organism applied alone. The effect o f these pseudomonads on G. clarum NT4 spore germination was investigat ed. Germination was inhibited when spores were incubated either on mem branes placed directly on bacterial lawns of strains R85 and R104 (i.e ., direct assay), or on agarose blocks separated from the bacteria by membranes (i.e., diffusion assay). When the agarose blocks were physic ally separated from the pseudomonad (i.e., volatile assay), there was no evidence of inhibition, suggesting that a nonvolatile, diffusible s ubstance(s) produced by both strains R85 and R104 may inhibit G. claru m NT4 spore germination.