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United States Department of Agriculture

Agricultural Research Service

Research Project: Biology and Biological Control of Root Diseases of Wheat, Barley and Biofuel Brassicas

Location: Root Disease and Biological Control Research

Title: Principles of Plant-Microbe Interactions - Microbes for Sustainable Agriculture

Author
item Weller, David

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 15, 2014
Publication Date: N/A

Interpretive Summary: Crops lack genetic resistance to most soilborne pathogens that are ubiquitous in agroecosystems worldwide. To overcome this disadvantage, plants recruit and nurture specific group of antagonistic microorganisms from the soil to defend their roots against pathogens and other pests. The best example of this microbe-based defense of roots is observed in disease-suppressive soils in which the suppressiveness is induced by continuously growing crops that are susceptible to a pathogen. Suppressive soils occur globally. One of the best described examples of soil suppressiveness is take-all decline (TAD), whereby the incidence and severity of take-all disease of wheat spontaneously decreases with continuous monoculture of wheat or barley. Take-all is the most important root disease of wheat worldwide, causing $2 billion in losses annually. TAD protects wheat on millions of acres worldwide and is an especially cost effective means to control take-all because it requires not off-farm inputs and utilizes the natural antagonistic microbes in the soil to defend the roots against disease. This book chapter provides a summary of what is known about TAD and it mechanism of action. It provides information that is useful to both the scientific community and farmers.

Technical Abstract: Crops lack resistance to many soilborne pathogens and rely on antagonistic microbes recruited from the soil microbiome to protect their roots. Disease-suppressive soils, the best examples of microbial-based defense, are soils in which a pathogen does not establish or persist, establishes but causes little or no disease, or establishes and causes disease at first but then the disease declines with successive cropping of a susceptible host. Take-all decline (TAD) controls take-all disease of wheat caused by Gaeumannomyces graminis var. tritici. TAD is a spontaneous reduction in the incidence and severity of take-all occurring with monoculture of wheat or barley following a severe disease outbreak. TAD suppressiveness is transferable, eliminated by soil pasteurization, and reduced by growing non-host crops. It results from the build-up of populations of 2,4-diacetytlphloglucinol (DAPG)-producing Pseudomonas spp. to a threshold density of at least log 5 CFU per gram of root. TAD protects wheat against take-all on millions of hectares worldwide.

Last Modified: 12/26/2014
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