Importance of phosphorus supply through endophytic Metarhizium brunneum for root:shoot allocation and root architecture in potato plants

Background and aims Recent studies indicate the potential of endophytic entomopathogenic fungi to promote plant growth but little is known about the responses of root architecture to fungal endophytism. This study investigates potential adaptations of root architecture upon Metarhizium brunneum endophytism linked to improved plant growth and nutrition. Methods Plants (Solanum tuberosum L.) were grown in the presence of M. brunneum applied either as nonformulated mycelium or as mycelium containing beads. After 35 days, fungal growth, root endophytism, plant biomass and nutrition as well as root attributes were determined. Results In response to endophytism promoted by bead application, plant P contents and biomass were significantly increased, while N contents and shoot allocation were also significantly increased in plants from the beads without mycelium group. Bead application resulted in a shift from fine to medium-sized roots and in an increase in the number of root forks, while root diameter, surface area and the number of root tips and crossings were independent of either bead or M. brunneum treatment. Conclusions M. brunneum containing beads supported endophytism allowing for increases in plant P contents and biomass. However, root architecture was not strongly modulated by M. brunneum endophytism with N provision through bead application being more important than fungal P delivery.