Eric Young

Chilling unit accumulation and forcing effects on carbohydrates of young apple rootstocks

Sucrose, glucose, hexose (glucose + fructose), and sorbitol were measured enzymatically in root and shoot tissues of young apple (Malus x domestica Borkh.) MM. Ill rootstocks during rest (0 to 2400 chilling units (CU) and 0 to 36 days of forcing (DF). Changes in starch and sorbitol concentrations during chilling and forcing were variable. Starch generally decreased with increasing chilling and forcing. Sorbitol showed little change with forcing. Sorbitol concentration generally declined until chilling was adequate for 50 to 90% budbreak (1200-1600 CU), then increased. The magnitude of changes was greater overall for starch in roots and for sorbitol in shoots. Sucrose and hexose concentrations in shoots and roots increased from 0 to 12 DF, remained relatively stable from 12 to 24 DF, and declined from 24 to 36 DF. Sucrose increased from 0 through 800 CU, decreased between 800 and 1200 CU (chilling requirement for 50% budbreak), and remained relatively stable from 1200 through 2400 CU. During rest, hexose d...

Growth dynamics of young apple trees as influenced by scion and rootstock vigour

Growth of young potted apple trees composed of ‘Classic Delicious’ (nonspur) or ‘Red- chief Delicious’ (spur-type) scions grafted onto O.P. Malus domestica L. (seedling) or Mailing 26 (M.26) rootstocks was observed during three growing seasons. Across rootstocks, spur-type ‘Delicious’ characteristics include lower whole-tree and shoot-wood dry weights, resulting in higher root/shoot ratios. Across scions, rootstock had little effect on dry weight of tree parts above the graft union, whole-tree dry weight or spur density. Trees on M.26 dwarfing rootstock had higher root shank and lower fibrous-root dry weights on all three sampling dates. Although few scion by rootstock interactions were detected, the spur-type scion on M.26 had the most spurs and flowers per metre of scion by the third growing season.

Influence of chilling at 5°C, IB A, suckering and top growth on root regeneration in seedlings of Malus spp.

SummaryFour experiments were conducted to separate the enhancement of root growth by chilling at 5°C from the promoting effects of the growth of new shoots and suckers (adventitious shoots from roots) during forcing in apple. Various combinations of low temperatures (5°C), detaching plants at the soil surface, girdling, and/or IBA were used to suppress new shoot and sucker growth during forcing after subjecting Malus seedlings to increasing levels of chilling. Following increasing duration of chilling at 5°C (CH), forcing intact Malus domestica Borkh. seedlings at a 20°C soil and air temperature caused initial bud- break, shoot extension, and root growth to occur earlier, faster, and to reach a greater final magnitude. Detaching M. domestica seedlings at the soil surface prior to chilling was ineffective as a means of separating root and top growth responses to chilling as it stimulated production of suckers and/or watersprouts near the soil surface. Root numbers and fresh weights in M. domestica, Malus a...