Differential resistance of oilseed rape cultivars (Brassica napus ssp oleifera) to Verticillium longisporum infection is affected by rhizosphere colonisation with antagonistic bacteria, Serratia plymuthica and Pseudomonas chlororaphis

The effect of a seed treatment with the antagonistic bacteria Serratia plymuthica (strain HRO-C48) and/or Pseudomonas chlororaphis (strain MA 342) on the infection of oilseed rape with Verticillium longisporum was assessed with ten different cultivars. Soil was inoculated with microsclerotia and mycelium of a V. longisporum culture. Seeds were treated with rifampicin-resistant antagonistic bacteria at a rate of log(10) 6-7 cells per seed. Resistance against V. longisporum infection did not differ between cultivars and was generally low. A significant disease reduction recorded as area under disease progress curve (AUDPC) was obtained with both antagonistic rhizobacteria with no significant difference between the treatments. Percent of healthy plants was approximately 70% in all bacterial treatments. Significant differences were observed between the cultivars ranging from 46.5% (cultivar Titan) to 72.6% (Trabant). The combined use of both bacteria could not provide additional control effects. The bacterial density in the rhizosphere was not related to the control effect, but increased by log(10) 2 on infection with V. longisporum. Growth promotion effects were also not related to the control effect. At present, neither the application of chemical fungicides nor breeding for resistance against V. longisporum in oilseed rape can provide a solution for this increasingly problematic plant pathogen. The present results now open perspectives to control V. longisporum in oilseed rape by making use of cultivars, which express resistance against this pathogen on interaction with the antagonistic rhizobacteria S. plymuthica or P. chlororaphis.