Rootstock effects on growth, bud development and flowering of apple [microform]

In a greenhouse study, the apple (Malus domestica Borkh.) cultivars 'Gala' and 'Delicious' were grown on a range of rootstocks known to produce widely differing tree sizes. Vegetative growth was largely controlled by rootstock, whereas flowering 2 years after grafting was higher in 'Gala' than 'Delicious' with no rootstock effect. In a field study with 'Delicious' growing on 17 rootstocks, shoot length was strongly related to trunk cross-sectional area (TCSA) but the slope of the relationship decreased as trees aged. Spur density was negative!y and weakly related to shoot length. Flower density was negatively related to both TCSA and shoot length, but was unrelated to spur density. Flower density and the proportion of spurs which flowered were strongly related. Rootstocks influenced flowering mainly by affecting the proportion of spurs which formed flowers rather than by modifying spur density.

Precocity and cumulative yield efficiency were unrelated to spur density, but were strongly negatively related to TCSA. Productivity after 10 years could be predicted with a high degree of certainty by TCSA in the fourth year. In each year, apical doming occurred during August for trees on all rootstocks. Rootstock affected the proportion of buds which initiated flowers in one of three years, where B.9 and M.7 EMLA produced more flowers compared with trees on other rootstocks. The number of appendages in buds of 'Starkspur Supreme Delicious' prior to doming was 20, and was constant among rootstocks and years. From 70 days after full bloom, increases in bud appendage number were primarily due to bract production, while the number of bud scales, transition leaves and true leaves remained constant. The phosphorus concentration of spur leaves declined over the course of the growing season, but was unaffected by rootstock in each of three years.

Similarly, the relative phosphorus content of bud apical meristems measured by EDAX analysis tended to decline over the growing season and was unaffected by rootstock. The calcium concentration of spur leaves was highest in trees on B.9 rootstock and tended to be lowest in trees on M.26 EMLA and seedling rootstock.