THE INTERACTION OF HIGHER PLANTS AND SOIL MICROORGANISMS

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Abstract
Two vars. of flax, Bison and Novelty, resistant and susceptible respectively to Fusarium wilt were grown in soil and under aseptic conditions in nutrient soln. The method of aseptic plant cultures is fully descr. Chemical analyses indicate that resistant var. excreted or diffused through the root system into the nutrient soln. 25 to 37 mg. of HCN per plant grown, whereas susceptible var. excreted only a trace. To study the influence of by-products of growth of flax vars. on the activity of soil micro-organisms the solns., obtained after plant growth, were allowed to diffuse through the collodion membranes into the surrounding soil[long dash]thus creating an artificial rhizosphere. The fungus population, which was studied in detail, of the natural and artificial rhizospheres of the corresponding vars. did not differ to an appreciable extent. However, the quantitative and qualitative fungus population of the natural as well as artificial rhizospheres of the resistant and susceptible varieties was significantly different. The lower moisture content (30%) of the soil resulted in more abundant fungus population in the rhizospheres of both vars. and the varietal difference was more clearly expressed. Fusarium and Helminthosporium responded beneficially to the soln. after growth of susceptible var. and yielded 14 and 3.5 times greater wts. of mycelial matter than the soln. after growth of resistant var. Tricho-derma, however, showed better growth on the media prepared with soln. after growth of a resistant var. KCN when added to Crone''s nutrient soln. (85 mg. per 100 ml.) excreted an effect on the growth of the same fungi analogous to that produced by the soln. after growth of resistant var.

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