Screening of rhizobacteria for antagonistic activity against Pythium ultimum on cucumber and kale

The bacteria studied originated from roots of field-or glasshouse-grown cabbage seedlings. Of 26 selected isolates with in vitro activity against Phoma lingam and/or Fusarium culmorum, 23 were identified as fluorescent pseudomonads, with Pseudomonas chlororaphis and Pseudomonas putida Biotype B constituting the largest groups. To evaluate their activity in vivo, bacteria were applied to seeds of cucumber and kale and rested simultaneously in the glasshouse for control of P. ultimum. Of the 144 isolates tested, about 30 % shelved activity against P. ultimum on cucumber or kale. In further rests with selected isolates, control of P. ultimum was better and more reliable on cucumber than on kale. The efficacy of Pythium control was lower when the pathogen inoculum was evenly mixed into rile potting substrate than when it was applied in a layer, although the infection pressure in pathogen checks was comparable. When the pathogen inoculum was applied in a layer, up to 96 % efficacy was observed on cucumber, equivalent to control with thiram (seed treatment) and propamocarb (soil drench). In two experiments on cucumber in which the Pythium inoculum was mixed into the substrate, the efficacy of the most active isolate was 56 % and 48 %, respectively (propamocarb: 84 %/75 %).