Abstract
The slender spindle bush type system is commonly used for compact-sized trees, especially grafted on dwarfing rootstocks. It is difficult to apply this system to trees grafted on vigorous rootstocks by winter pruning. Such practices only cause the trees to repeat imbalanced vegetative-oriented growth every year. Therefore, in the current work summer pruning was applied to slender spindle bush type of early maturing peach trees grafted on vigorous rootstocks. Three trials were conducted: summer shoot thinning, shoot heading back trials in the field and a shoot heading back and shading trial in the pot experiment. Summer shoot thinning reduced tree growth and recovered proper balance between vegetative and reproductive growth. The following season such shoot thinning enhanced bud burst and initial growth of new shoots but the final tree growth was less in the summer-pruned trees compared with winter-pruned trees. The fruit matured earlier and soluble solids content was greater and titratable acidity was lower in the summer-pruned trees. The summer shoot heading back trial revealed that it regenerates shoots, although they bear fewer flower buds compared with winter-pruned trees. Such heading back is effective to keep alive shoots and buds near the trunk in slender spindle bush type systems. Summer shoot heading back and shading experiments in the pot showed that shading reduced the number of regenerated shoots and flower bud formation and delayed flower blooming in the following year. Thus summer shoot thinning and heading back are applicable to early maturing peach cultivars grafted on vigorous rootstocks to maintain the slender spindle bush type because thinning favors reducing tree vigor and light penetration near the trunk, and heading back keeps alive shoots and buds near the trunk which otherwise weaken or die back due to apical dominance and/or shading.
