Pre-colonisation of strawberry runners and tray plants with arbuscular mycorrhizal fungi to manage Verticillium wilt

Strawberry wilt, caused by Verticillium dahliae Kleb., can reduce yield by up to 75%. For c. 40 years, soil was routinely fumigated with methyl bromide until it was banned by the 1994 Montreal Protocol which became effective in the UK in 2006. Another fumigant, chloropicrin, is to be withdrawn from Europe in 2013. Extensive effort has gone into finding alternatives. Among these, incorporation of green manures that release volatile fungitoxic compounds, so-called biofumigation, shows promise as a component of a disease management strategy.
In a recent Hort-LINK project, a group of scientists led by EMR demonstrated that lavender waste can effectively reduce Verticillium wilt severity on strawberry and identified three key terpenoids responsible for the observed suppressive effect. In a follow-on TSB project, EMR is leading a consortium to investigate whether pelletised lavender waste and microencapsulated terpenoids can effectively control strawberry wilt. Results so far, however, indicate limited efficacy of these products. Thus, other measures in addition to the biofumigation-based approach are needed.
Arbuscular mycorrhizal fungi (AMF) are ubiquitous in terrestrial ecosystems where they are major components of the soil microbial biomass. Mycorrhizal associations are multi-functional, assisting the plants in nutrient acquisition, water uptake, and protecting roots from pathogens. AMF have been shown to increase plant tolerance to V. dahliae on several crops, including pepper, strawberry and cotton. However, the beneficial effects offered by AMF can vary considerably.
A recent publication showed that one particular AMF strain significantly reduced strawberry wilt when plants were inoculated at planting. The extent of AMF root colonisation and their beneficial effects to plants are however also dependent on particular AMF strains and strawberry cultivars. Ensuring sufficient colonisation of strawberry planting materials (runners or tray plants) before trans-planting may further increase the benefit of AMF-symbiosis through physical exclusion of potential colonisation sites for soil pathogens.