NATURAL SUPPRESSION OF TAKE-ALL DISEASE OF WHEAT IN MONTANA SOILS

This research was initiated to determine whether soils suppressive to take-all of wheat caused by Gaeumannomyces graminis var. tritici (Ggt) occur in Montana, and to identify the organisms most likely involved in this suppression. From an initial screening of eight soils collecte d from different wheat growing areas of Montana, two were highly suppr essive to take-all. Microbial characterization of these soils indicate d that different mechanisms were involved in the suppression. In Larsl an soil, mycoparasitism appeared to be the main mechanism. Two differe nt fungi with exceptional ability to reduce the severity of take-all w ere isolated from this soil. One of these fungi could parasitize the h yphae of Ggt. Field tests with these fungi in Ggt infested soil showed increases of over 100% in both harvestable tillers and grain yield as compared to treatments without these two fungi. In tests with 48 diff erent bacteria and 10 actinomycetes from Larslan soil, none were able to consistently reduce severity of take-all alone, or in mixtures. In Toston soil, antibiosis by actinomycetes and perhaps the involvement o f Pseudomonas spp. in production of antibiotics and/or siderophores ap peared to be the most likely mechanisms involved in take-all suppressi on. Increases in shoot dry weight over that in the Ggt infested contro l using mixtures of pseudomonads and actinomycetes ranged from 25% to 87%. Actinomycetes added individually or in mixtures to soil infested with Ggt consistently reduced the severity of the disease to a greater extent than did mixtures of Pseudomonas spp.