Effects ofPseudomonas fluorescenson Potato Plant Growth and Control ofVerticillium dahliae

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Abstract
Pseudomonas fluorescens strain M-4, an antagonist of Verticillium dahliae in vitro, was studied to determine its potential as an inhibitor of V. dahliae and growth promoter of potato plants. In pot experiments of soil fortified with V. dahliae, fresh weight of shoots and roots and plant height from potato seed pieces dusted with P. fluorescens were significantly greater for plants treated with P. fluorescens. In addition, the number of propagules of V. dahliae in stem tissue was significantly lower for treated potatoes. In pasteurized soil, potato growth was not enhanced by P. fluorescens, even though the roots were colonized by the bacteria significantly more than in soil infested with V. dahliae. In 1982 and 1984 field trials, P. fluorescens applied to hand-planted seed pieces as a dust or liquid coating containing 108 cfu/ml resulted in root population densities of about 104 cfu/g of root, similar to populations on roots in greenhouse pot experiments. In the field, however, P. fluorescens had no effect on yield, percent U.S. No. 1 tubers, or incidence of Verticillium wilt.