Risto Tahvonen

Biological control of strawberry crown rot is substrate dependent phenomenon

BACKGROUND: Phytophthora cactorum crown rot is currently limiting strawberry cultivation worldwide. Arbuscular mycorrhizal fungi (AMF) and bacterial endophytes have shown promising results as biological control against the disease. Growing medium can also influence biological control and e.g., composts have been shown to suppress soil borne pathogens. OBJECTIVE: The aim of the study was to investigate the effect of AMF, endophytic bacteria and different growing media against strawberry crown rot. METHODS: Three pot experiments were conducted in greenhouse conditions. Each experiment tested different biological control methods with micropropagated strawberry ‘Jonsok’ inoculated or not with the fungus. The first experiment evaluated AMF strains on different growing media, the second experiment tested combinations of AMF and other biocontrol microbes. The third experiment tested the impacts of AMF, Pseudomonas fluorescens and compost. RESULTS:Biological control methods and disease inoculation had very different impacts on strawberries planted in different growing media. On suitable growing media, AMF increased growth and lowered disease symptoms, but P. fluorescens was not effective. The growing medium containing manure/wood fiber compost was the most disease suppressive. CONCLUSIONS: Biological control of strawberry crown rot with AMF is substrate dependent. Composts can be used to somewhat suppress crown rot.

The phytotoxicity of disinfectants and their effect at different temperatures

When disinfecting plastic growth containers, only sodium hypochloride (NaCIO) caused damage both to cucumber and lettuce seedlings grown on peat if the containers had not been washed with water after disinfection. Also the seedlings grown on rockwool cubes were susceptible to Menno-Ter-forte when the growthcontainers were not properly rinsed after disinfection. All tested disinfectants caused damage to cucumber, lettuce and cauliflower seedlings when mixed in the peat substrate. The efficiency of disinfectants was higher at +2O°C than at +5°C, especially against Fusarium culmorum, F. oxysporum and Rhizoctonia solani. A decrease in temperature affected least the efficacy of NaOCl and Menno-Ter-forte and most that of Virkon S.