Take-all decline and beneficial pseudomonads

Abstract

Crops lack resistance to many soil borne 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 105 CFU g−1 root. TAD protects wheat against take-all on millions of hectares worldwide.