Reduction in Fusarium Population Density in Soil by Volatile Degradation Products of Oilseed Meal Amendments

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Abstract
Soybean, linseed and cottonseed meals incorporated into a loamy sand soil at 1% concentration (wt/wt) reduced chlamydospore population densities of F. oxysporum and F. solani from 105/g to 102/g or less after 4-6 wk incubation in closed containers. Incubation of similarly amended soil in open containers was less effective in reducing chlamydospores. No decrease in population density was observed in alfalfa meal-amended and unamended soils. Propagule densities of 5 additional Fusarium spp. [F. lateritium Nees, F. moniliforme Shelf., F. rigidiusculum (Brick) Snyd. and Hans., F. roseum (Lk.) Sacc., and F. tricinctum (Corda) Sacc.] incubated in soil above, but not in contact with, amended soil in closed containers also were significantly reduced. Boric acid solutions above oilseed meal-amended soils nullified the fungitoxic effect produced by soybean meal, but not that produced by linseed or cottonseed meals. The greatest amounts of titratable substances trapped in boric acid solution were produced with soybean meal, followed in order by linseed and cottonseed meals. NH3, .apprx. 1000-4000 .mu.g/ml, was detected by multicolumn gas chromatography of the trapping solutions. Relative concentrations of NH3, were in the order: soybean meal > linseed meal > cottonseed meal. The quantity of NH3, produced was inversely related to the C:N ratios of the meals. The evidence indicates that NH3, was involved in suppression of Fusarium by the oilseed meal amendmdnts, but other unidentified compounds also were involved in suppressing Fusarium in soils amended with either linseed or cottonseed meals. In the presence of the oilseed meals, Fusarium chlamydospores were first stimulated to germinate, then new chlamydospores were formed, but these were soon killed. In soil amended with alfalfa meal, chlamydospore germination also was stimulated and was followed by the formation of new chlamydospores, but these remained viable.

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