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Phenazine Production by Pseudomonas sp. LBUM223 Contributes to the Biological Control of Potato Common Scab

October 2013 , Volume 103 , Number  10
Pages  995 - 1,000

Tanya Arseneault, Claudia Goyer, and Martin Filion

First and third authors: Université de Moncton, Department of Biology, Moncton, NB, Canada; and second author: Potato Research Center, Agriculture and Agri-Food Canada, Fredericton, NB, Canada.

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Accepted for publication 28 April 2013.

Common scab of potato is mainly caused by Streptomyces scabies. Currently, no method can efficiently control this economically important disease. We have previously determined that Pseudomonas sp. LBUM223 exhibits antagonistic properties toward S. scabies under in vitro conditions. Inhibition was mainly attributed to phenazine-1-carboxylic acid (PCA) production because an isogenic mutant of LBUM223 (phzC–), not producing PCA, was incapable of significantly reducing S. scabies growth. In order to understand the impact of PCA production by LBUM223 in controlling common scab under soil conditions, pot experiments were performed to determine its effect on (i) reducing scab symptoms development, (ii) S. scabies population dynamics, and (iii) txtA expression in S. scabies, a key gene involved in thaxtomin A biosynthesis and required for pathogenesis. Symptoms were significantly reduced following inoculation with LBUM223 but not its mutant. Surprisingly, pathogen populations increased in the geocaulosphere in the presence of both wild-type and mutant strains of LBUM223; however, significant repression of txtA expression in S. scabies was only observed in the presence of PCA-producing LBUM223, not its mutant. These results suggest that, under soil conditions, PCA production by LBUM223 does not control common scab development by antibiosis but, instead, reduces S. scabies thaxtomin A production in the geocaulosphere, leading to reduced virulence.

© 2013 The American Phytopathological Society