Disease-suppressive soils induce systemic resistance in Arabidopsis thaliana against Pseudomonas syringae pv. tomato

Abstract

Arabidopsis thaliana accession Col-0 seedlings were transferred into an autoclaved potting soil/sand mixture amended with either 10 or 20% (weight/weight) soil from fields in Washington State USA that are suppressive to take-all or Rhizoctonia root rot of wheat. Three weeks after transplanting, these plants had population sizes of 2,4-diacetylphloroglucinol (DAPG)- or phenazine-1-carboxylic acid (PCA)-producing pseudomonads of greater than 5 x 105 colony forming units per gram fresh weight of root with rhizosphere soil. When the plants were challenge-inoculated with Pseudomonas syringae pv. tomato, both soils displayed induced systemic resistance in the leaves against bacterial speck to a level similar to that induced by Pseudomonas simiae WCS417r, P. fluorescens Q2-87 (DAPG+), P. brassicacearum Q8r1-96 and L5.1-96 (both DAPG+), and P. synxantha 2-79 (PCA+). Pasteurization of the soils before adding them into the soil/sand mixture eliminated DAPG- and PCA-producing pseudomonads from the A. thaliana rhizosphere and significantly reduced induced systemic resistance activity. However, populations of total culturable heterotrophic aerobic bacteria were similar in the rhizosphere of plants grown in soil/sand mixes amended with untreated or pasteurized suppressive soils. This is the first report of induction of systemic resistance in A. thaliana by take-all and Rhizoctonia suppressive soils and the ability of PCA-producing P. synxantha 2-79 to induce resistance.