NATURAL PLANT-PROTECTION BY 2,4-DIACETYLPHLOROGLUCINOL - PRODUCING PSEUDOMONAS SPP. IN TAKE-ALL DECLINE SOILS

Take-all decline (TAD) is a natural biological control of the wheat ro ot disease ''take-all'' that develops in response to the disease durin g extended monoculture of wheat. The research to date on TAD has been mostly descriptive and no particular occurrence is yet fully understoo d. We demonstrate that root-associated fluorescent Pseudomonas spp. pr oducing the antibiotic 2,4-diacetylphloroglucinol (PN) are key compone nts of the natural biological control that operates in TAD soils in Wa shington State (U.S.A.). Phl-producing Pseudomonas spp, were present o n roots of wheat grown in TAD soils at or above the threshold populati on density required for significant suppression of take-all of wheat. The specific suppression that operates in TAD soils was lost when Phl- producing fluorescent Pseudomonas spp. were eliminated, and conducive soils gained suppressiveness to take-all when Phl-producing Pseudomona s strains were introduced via mixing in small amounts of TAD soil. Int roduction of selected Phl-producing strains into take-all conducive so ils provided control of take-all of wheat to a level similar to that o btained in the complementary TAD soils.