Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/1997
Publication Date: N/A
Interpretive Summary: Soilborne plant pathogens are major yield-limiting factors in the production of food, fiber and ornamental crops. Take-all, caused by the fungus Gaeumannomyces graminis var. tritici (Ggt), is the most important root disease of wheat in the U.S. and worldwide. Interest in the use of microbial biocontrol agents to suppress soilborne plant pathogens has been stimulated in recent years by trends in agriculture toward greater sustainability and public concerns about hazards associated with the use of chemical pesticides. Take-all can be suppressed by a variety of soil micro- organisms including fungi such as Trichoderma spp. However, within a region, the level of protection provided by Trichoderma can dramatically vary between field sites. The purpose of this research was to evaluate the biocontrol activity of Trichoderma koningii in field soils representative of the wheat-growing region in the Pacific Northwest in order to identify those regions in which Trichoderma whould be most effective. In addition, the chemical and physical factors of the soil that are positively or negatively related to the biocontrol activity of T. koningii were identified. A model was developed based on soil factors that predicts those soil in which Trichoderma will be most and least effective. Potential applications of these results include amending soil with benefical factors that may be lacking in the target soil and better targeting of biocontrol treatments to sites where they will be most effective.
Technical Abstract: Trichoderma koningii, originally isolated from a take-all-suppressive soil in Western Australia has been shown to protect wheat against take- all disease and increase grain yield in field trials in Australia, China, and the United States. However, within a region, the level of protection n provided by T. koningii can dramatically vary between field sites. We evaluated suppression of take-all by this fungus in eight silt loams from the Pacific Northwest of the United States and the influence of 21 abiotic soil parameters on biocontrol activity. While T. koningii significantly increased plant growth and reduced disease severity in all eight silt loams, the level of protection varied significantly among the soils. Disease suppression was not associated with the conduciveness of a soil to take-all, but rather to the supportiveness of a soil to biocontrol activity. Biocontrol activity was positively correlated with iron, nitrate-nitrogen, boron, copper, soluble magnesium, and percent clay, and negatively correlated with soil pH and available phosphorous. Principal component factor analysis using these eight variables resulted in a three-component solution that accounted for 95% of the variation in disease rating. Least square regression analysis (R2=0.992) identified a model that included nitrate-nitrogen, soil pH, copper, and soluble magnesium, and described the variance in take-all suppression by T. koningii.