INFLUENCE OF PH ON SUPPRESSION OF FUSARIUM-WILT OF CARNATION BY PSEUDOMONAS-FLUORESCENS WCS417R

The influence of the nutrient solution pH on suppression of fusarium w ilt by Pseudomonas fluorescens WCS417r in carnation grown in rock-wool was investigated. Experiments were conducted with carnation cultivars Lena and Pallas, susceptible and moderately resistant to fusarium wil t, respectively. WCS417r significantly reduced fusarium wilt in the su sceptible cv. Lena, that was root-inoculated with Fusarium oxysporum f .sp. dianthi (Fod), at pH 7.5, but not at pH 6.5 and 5.5. This corresp onded with a higher in vitro siderophore production and antagonism of Fod by WCS417r at pH 7.5 than at pH 6.5 and 5.5. Fusarium wilt in the moderately resistant cv. Pallas, however, was also significantly reduc ed by treatment with WCS417r at pH 5.5. This corresponded with the low influence of pH on induced resistance by WCS417r in plants of cv. Pal las that were stem-inoculated with Fod. The results indicate that the influence of pH on control of fusarium wilt of carnation by Pseudomona s fluorescens WCS417r differs between carnation cultivars that differ in their level of resistance against fusarium wilt. In susceptible cv. Lena, fusarium wilt is suppressed by antagonism by WCS417r, that is m ost effective at pH 7.5. In the moderately resistant cv. Pallas, fusar ium wilt is suppressed by both antagonism and induced resistance by WC S417r. The latter is also effective at lower pH.