Arbuscular mycorrhizal fungal-induced alteration to root architecture in strawberry and induced resistance to the root pathogen Phytophthora fragariae.
Strawberry cv. Elsanta, Cambridge Favourite and Rhapsody plants were soil inoculated with Glomus fasciculatum or G. etunicatum or not inoculated. 55-71% of roots of all inoculated plants were colonised after 98 days. Increases in both root and shoot dry weights were measured. Root architecture was also determined and increases in branching were evident in arbuscular mycorrhizal fungi (AMF) colonised root systems. The remaining plants were then inoculated with the root pathogen P. fragariae and allowed to grow for a further 58 days before harvest. In Cambridge Favourite and Elsanta, AMF reduced root necrosis by approximately 60 and 30% respectively. Only in the least susceptible cultivar, Rhapsody, was no reduction measured in AMF colonised plants. There were differences in the control conferred by the two AMF and this suggests there may be practical benefits of inoculation. Relationships between the presence of roots of different orders, on inoculation with the pathogen, and subsequent necrosis provided a mechanism for identifying root-architecture driven alteration to susceptibility. Root system necrosis was positively correlated with the proportion of the root system made up of higher order roots (3° to 4°) in non-colonised plants and negatively correlated in AMF colonised plants. It is concluded that root-architecture changes are not important per se but factors expressed concurrently may be.