Growth stimulation of apple trees in unsterilized soil under field conditions with VA mycorrhiza inoculation

Apple seedlings germinated and grown under greenhouse conditions were inoculated with endomycorrhizal roots originating from a nursery grown Fraxinus prior to outplanting into unsterilized field soil. Uninoculated seedlings, in soil either unamended or amended with 100 kg/ha P as superphosphate, were controls. Shoot length, leaf surface, root volume, stem diameter, and dry mass of inoculated plants were all significantly greater than both fertilized and unfertilized controls. No significant difference could be observed in foliar mineral content but the level of N, P, Ca, Cu, and possibly K were higher in the roots of inoculated plants than in controls. Although shoot length of the phosphorus fertilized plants exceeded that of the unfertilized controls (p < 0.05), all the other growth parameters remained unchanged by the addition of P. Intracortical vesicles were absent or very uncommon in the roots of both fertilized and unfertilized control plants whereas they were very abundant in the roots of inoculated plants.It is concluded that inoculation of seedlings previous to field planting in unsterilized phosphorus-poor soil can lead to a significant growth stimulation in spite of the presence of a natural endomycorrhizal flora.