Canopy structure and light interception partitioning among shoots estimated from virtual trees: comparison between apple cultivars grown on different interstocks on the Chinese Loess Plateau

Dwarf interstock produced smaller tree size and a more uniform leaf area spatial distribution of vegetative short shoot. These improved light interception and increased light partitioning to fruiting shoot. The agronomic efficiency of dwarf interstocks is controversial in China, where almost 90 % of apple orchards, including high-density orchards, currently use vigorous rootstock. We quantified the influence of dwarf interstock on canopy structure and light interception in two apple cultivars commonly grown on the Chinese Loess Plateau. 'Fuji' and 'Gala' apple trees were grafted onto two rootstock/interstock combinations: M. micromalus/M. domestica cv. 'Qinguan', a vigorous interstock and M. micromalus/M26, a dwarf interstock. Nineteen trees, grown with the spindle training system, were digitized and allometric relationships were determined for all shoot types before harvests in 2011 and 2012. Virtual three-dimensional canopies were reconstructed and light interception was evaluated. The spatial distribution of leaf area density of vegetative short shoot was more uniform on dwarf interstock compared to the vigorous interstock. These improvements led to higher light interception efficiency in dwarf interstock trees. There were fewer poorly illuminated within-tree zones and shoots on dwarf interstock than on vigorous interstock. The dwarf interstock trees showed a 25 % silhouette to total leaf area (STAR) increase for the whole tree and 21 and 17 % STAR increases for fruiting shoots and vegetative short shoots, respectively. 'Fuji' foliage was more clumped than 'Gala', leading to lower light interception. The results indicate that dwarf interstocks can effectively improve light interception efficiency.