Biological control of fungal strawberry diseases by Serratia plymuthica HRO-C48

To develop a biological control product for commercial strawberry productio n, the chitinolytic rhizobacterium Serratia plymuthica strain HRO-C48 was e valuated for plant growth promotion of strawberries and biological control of the fungal pathogens Verticillium dahline and Phytophthora cactorum. In phytochamber experiments, treatment with S. plymuthica HRO-C48 resulted in a statistically significant enhancement of plant growth dependent on the co ncentration of the bacterium that was applied. In greenhouse trials, bacter ial treatment reduced the percentage of Verticillium wilt (18.5%) and Phyto phthora root rot (33.4%). In three consecutive vegetation periods, field tr ials were carried out in soil naturally infested by both soilborne pathogen s on commercial strawberry farms located in various regions of Germany. Dip ping plants in a suspension of S. plymuthica prior to planting reduced Vert icillium wilt compared with the nontreated control by 0 to 37.7%, with an a verage of 24.2%, whereas the increase of yield ranged from 156 to 394%, wit h an average of 296%. Bacterial treatment reduced Phytophthora root rot by 1.3 to 17.9%, with an average of 9.6%, and increased strawberry yield by 60 % compared with the nontreated control. Under field conditions, strain HRO- C48 survived at approximately log(10) 3 to 7 CFU/g of root in the strawberr y rhizosphere at 14 months after root application. Although results of the field trials were influenced by pathogen inoculum density, cropping history of the field site, and weather conditions, S. plymuthica HRO-C48 successfu lly controlled wilt and root rot of strawberry.