Rootstock effects on the flowering of 'Delicious' apple. II. Nutritional effects with specific reference to phosphorus

In each of 3 years, vegetative spurs were sampled from 1-year-old wood of 'Starkspur Supreme Delicious' apple trees (Malus domestica Borkh.) growing on B.9, M.26 EMLA, M.7 EMLA, P.18, and seedling rootstocks. Mineral concentrations of spur leaves and bud apical meristems were determined, and related to spur bud development. The spur leaf P concentration decreased during the growing season each year, but was unaffected by rootstock. Spur leaves of trees on B.9 rootstock had 30% higher Ca concentrations than trees on M.26 EMLA or seedling rootstocks. In each year, trees growing on M.26 EMLA rootstocks had the highest leaf Mg concentrations. Mineral concentrations were generally unrelated to spur leaf number, leaf area, leaf dry weight, or specific leaf weight. Phosphorus concentrations in spur bud apical meristems declined during two of the three growing seasons of the study and were unaffected by rootstock. Bud P concentration was weakly negatively related to bud diameter and bud appendage number in one year of the study. More vigorous spurs (as indicated by higher spur leaf number, leaf area, and leaf dry weight) had higher bud K levels during each year. No relationships between bud development and either spur leaf mineral concentration or bud apical meristem mineral levels were evident, suggesting that a direct role of mineral nutrition influenced by rootstock at the site of flower formation was unlikely