Nursery tree design modifies annual dry matter production of newly grafted ‘Royal Gala’ apple trees

Abstract

Total annual dry matter production of apple trees is correlated with the total amount of solar radiation intercepted by their leaf canopy. This fundamental principle has application in maximising the seasonal growth, size and quality of newly propagated apple trees. In this study, we grafted ‘Royal Gala’ scions (Malus×domestica Borkh.) onto one-year-old rootstock stools of ‘Malling 9’ (‘M9’) in winter, and grew trees in the subsequent spring with either one (monoaxis) or two (biaxis) primary axes per tree, to compare how each nursery tree design modified leaf area development, dry matter production and floral precocity. From 20 days after spring budbreak onward, biaxis trees had produced significantly more dry weight of leaf, scion and whole tree. For the first 120 days of growth, the period where no sylleptic shoots were present for either treatment, the total leaf area and dry weight of biaxis trees were greater than those of monoaxis trees, and trees that had a greater total leaf area also had a greater total tree dry weight. By growth cessation in late autumn, the final dry weight of tree was 35% higher for biaxis than for monoaxis trees, with biaxis trees showing greater dry weight gain in both the root system and scion. In the following spring, biaxis trees had a higher percentage of buds (15%) that were floral than monoaxis trees. We conclude that early-season leaf area development, which is necessary for light interception and photosynthesis, is an important factor limiting dry matter accumulation of newly grafted apple trees. The greater final biomass present in both root and scion of one-year-old biaxis nursery trees may contribute to accelerated canopy development of the planted orchard, while their greater flowering intensity indicates high potential for early cropping.