| A
regional study was made to identify vesicular-arbuscular mycorrhizal (VAM)
fungi effective in promoting plant growth in diverse plant and soil systems.
Eight cooperators in six states of the eastern United States evaluated six
VAM fungal isolates on soybean (Glycine max L. Merr.) and sorghum
(Sorghum bicolor L. Moench) in a shared soil and in at least one
regional soil from each location. Plants were grown with high VAM inoculum
densities (minimum of 20 VAM propagules/ml) for 42-57 days in pasturized
soils in greenhouses or growth chambers. Shoot and root dry masses, total
and colonized root lengths and shoot-P concentrations were determined at
harvest. Under the experimental conditions tested, the VAM fungal isolate
was more important than the soil or host plant in determining effectiveness.
In the shared soil, inoculation with two isolates of Glomus (GE329
and GENPI) resulted in the greatest shoot masses for soybeans, while the
same two isolates and GE312 provided maximum response in sorghum. In the
regional soils, GE329 and GENPI had the widest range of growth promotion
with both soybean and sorghum; however, for both plant species the mycorrhizal
response was greatest in soils with less than 10 mg/kg of extractable phosphorus.
For soybeans, colonized root length was not related to VAM growth response.
For sorghum, there was a positive correlation between colonized root length
and plant growth response. We conclude that VAM isolates exist which are
effective in promoting plant growth over a range of edaphic and host conditions. |
|