Arbuscular mycorrhizal fungi pre-colonisation for improving the growth and health of strawberry (Fragaria x ananassa)

Pre-colonisation of plants with arbuscular mycorrhizal fungi (AMF) before trans-planting has been proposed as a method for protecting crops against biotic and abiotic stresses and/or increasing plant productivity. Strawberry (Fragaria x ananassa) production systems make AMF pre-inoculation at the weaning stage relatively straightforward for in vitro and runner-derived plantlets. Strawberry plugs were pre-inoculated with different AMF species to study (1) whether AMF could pre-colonise different strawberry cultivars under high moisture and soil-less substrate during the weaning process, (2) whether AMF could survive the required artificial freezing cold storage of strawberry plugs for several months, and (3) whether AMF could enhance plant tolerance against Verticillium dahliae, Phytophthora fragariae and P. cactorum. In addition, (4) AMF was inoculated at planting to study whether AMF could increase strawberry growth and yield when cultivated in coir, and (5) a simple in vitro autotrophic system was also designed to investigate strawberry-AMF-pathogen interactions under controlled conditions. The study demonstrated that the soil-less substrates tested and high moisture conditions during tipping did not prevent different AMF from colonising roots of strawberry plugs. Pre-inoculated AMF species could also survive cold storage at -2°C with strawberry plugs for several months. However, AMF pre-colonisation and/or AMF inoculation at planting did not increase plant tolerance against root pathogens. It was demonstrated that AMF inoculation in coir did not significantly increase plant growth and yield. Finally, micropropagated strawberry were successfully infected by P. fragariae in vitro with the corresponding disease symptoms, while V. dahlia and AMF could germinate but did not colonise the strawberry roots in the autotrophic culture system. This is, to the best of our knowledge, the first research focusing on the AMF-strawberry interaction as a model system to study the possibility to pre-colonise strawberry plug materials to increase plant productivity and tolerance against major strawberry root diseases.