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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #77192
Title: BACTERIA FROM RHIZOSPHERE AND HYPHOSPHERE SOILS OF DIFFERENT ARBUSCULAR-MYCORRHIZAL FUNGI

Author
item ANDRADE, G
item Mihara, Keiko
item Linderman, Robert
item Bethlenfalvay, Gabor

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Mycorrhizal fungi colonize the roots of most crop plants and enhance their growth and resistance to stress. The introduction of effective fungi to problem soils is therefore a biological technique that can be utilized to help solve agricultural problems, such as nutrient deficiency or drought stress. The fungi, however, do not only live in close association with the roots of their host plants, but also with soil bacteria that colonize the surface of their soil hyphae. Recent work on these associations indicates that beneficial mycorrhiza effects on plant growth and yield is influenced by the associated bacteria. This effect is little known to date. We have investigated fungus-bacterium associations on sorghum, and found that different fungi tend to associate with different bacteria. Also, different bacterial groups occurred in soils colonized by the fungi associated with roots, compared to sterilized soil containing roots only. The findings suggest, subject to further research, that mycorrhizal inocula currently in commercial use could be improved by including specific fungus-associated bacteria. Such improved inocula may increase the effectiveness of mycorrhizal fungi in such applications as phosphorus uptake, biological control of pathogens, or soil stabilization.

Technical Abstract: Bacteria have been observed growing around arbuscular mycorrhizal (AM) fungal hyphae on water agar, suggesting that they use hyphal exudate as nutrient substrate. We studied mycorrhizosphere bacteria on sorghum roots in 45 day old pasteurized soil pot cultures. Plants were inoculated with two different isolates each of three AM fungal species, or were left uninoculated (7 treatments). Bacterial populations in the rhizosphere soil or soil colonized by AM fungal hyphae were counted after plating on TSA medium for total bacteria or P1 medium for fluorescent pseudomonads. Twenty-three isolates (with CFUs greater than 10**5) from rhizosphere soil or hyphosphere soil were selected for taxonomic study. The results suggested that specific AM fungi selectively stimulated populations of specific bacterial strains in hyphosphere soil that were not detected in the rhizosphere soil. Thus, different fungus-bacterial associations, both qualitative and quantitative, occur in the mycorrhizosphere soil that potentially can have different effects on plant growth and health. Further studies are needed to determine the functional attributes of specifically selected bacteria on plants.