Root system architecture in reciprocal grafts of apple rootstock-scion combinations

Many studies have demonstrated the effects of rootstocks on the growth and architecture of scions, but there has been comparatively little study of the physiological effects of scions on the performance of rootstocks. Three commercially available apple rootstocks conferring differing levels of vigour, M.27 (highly dwarfing), M.9 (dwarfing) and M.116 (semi-invigorating) were used as both rootstock and scion in reciprocally grafted combinations to determine the effect of the scion upon the rootstock and root system architecture (RSA). The trees were grown in thin rhizotrons (100 cm height, 30 cm width and 3 cm depth) containing loam and placed in a heated glasshouse with supplementary lighting and fertigation. The root systems were photographed with a DSLR camera at monthly intervals for a period of five months, and the images analysed using SmartRoot and MATLAB software to determine total root length and root diameter frequency. The height and stem diameter of the scions were also measured. Differences in total root length and root distribution were apparent after five months. M.27 had a shallow and fibrous root system whereas M.116 had a deep and coarse root system with more lateral roots appearing deeper in the soil. Our results show that the scion can have a significant effect that manifests as changes to the RSA, however, the extent of these changes are dependent upon the rootstock-scion combination.