In 1987, `Starkspur Supreme Delicious' and `Melrose' were planted on eight apomitic apple selections made in Germany by Dr. Hanna Schmidt for use as rootstocks and compared to trees on M.7. Selection 2, was the most precocious, followed by trees on M.7, with selections 1 and 7 being less precocious than M.7. Selections 2 and 8 were 25% larger than M.7, while 1, 3, 4, and 7 were similar in size and 5 was 15% smaller than trees on M.7. Selections 2 and 8 had the highest cumulative yields/tree, followed by trees on M.7, with all other selections having lower yields. Internal bark necrosis (IBN) developed on the `Delicious' trees, with the most-severe symptoms on selections 1, 3, 4, 5, 6, and 7, with less-severe symptoms on 8 and very little present on trees on M.7. IBN was correlated with leaf Mn levels. In 1995, the highest density of flowering spurs occurred on M.7 and selections 3 and 7, with lower densities in selections 2 and 5. Selection 2 had the highest density of non-fl owering spurs, followed by selection 5, with all others having lower densities similar to trees on M.7.
`Melrose'/M.26 apple (Malus domestics Borkh.) trees were mechanically root-pruned annually for 9 years at bloom to a 25-cm depth at 80 cm from the trunk on two sides. An evaluation of the number of roots of four size categories on the exposed wall of a 1.2 x 2-m trench located 1 m from the trunk indicated that root pruning caused a reduction in all root size categories. Roots < 1 mm in diameter were reduced 20% by root pruning, while the reduction in larger roots was nearly double this amount. The effect of root pruning on root distribution was greatest in the top 30 cm of soil, parallel to the location of the root-pruning cut. Roots below 30 cm were unaffected. The number of roots in all size categories in samples taken parallel and perpendicular to the row decreased linearly with soil depth.
The apple (Malus ×domestica Borkh.) cultivars Starkspur Supreme Delicious and Melrose were planted in 1987 on eight apomictic apple rootstock selections made in Germany by Dr. Hanna Schmidt and on M.7. Selections 2 [M. hupehensis (Pamp.) Rehd. parentage] and 8 [M. sieboldii (Regel) Rehd. parentage] were similar to M.7 in precocity, cumulative yield per tree, and yield efficiency, while the other selections with M. sargenti Rehd. in their parentage were slower to flower and had lower yields and yield efficiencies. Selections 2 and 8 tended to result in larger trees than M.7, while the selections with M. sargenti parentage were generally similar to M.7 in size. Except for trees on M.7 and selection 2, `Starkspur Supreme Delicious' developed more severe symptoms of internal bark necrosis (IBN) than did `Melrose', which normally does not show IBN. However, `Melrose' showed IBN symptoms on selections with M. sargenti parentage. IBN symptoms were positively correlated with leaf Mn concentrations. Influence of rootstocks on other nutrient elements, although significant, were small compared to the effect on Mn. A significant interaction occurred between cultivar and rootstock in their effects upon branch morphology, mostly because fewer flowering spurs and more vegetative spurs were observed on `Melrose' than on `Starkspur Supreme Delicious' when grafted on Selection 2. These apomictic selections offered no advantage over M.7 as rootstocks for apples.
Container-grown apple trees on a range of rootstocks were exposed to different levels of soil compaction created by changing soil bulk density. In 1998, with soil bulk densities of 1.0, 1.2, and 1.4, there was no interaction of rootstock and soil compaction for shoot growth of `Melrose' trees on 7 rootstocks. However, in 1999, with soil bulk densities of 1.0 and 1.5, a significant interaction on shoot growth did occur with six rootstocks. Shoot length of trees on M.9, M.7, and G.30 were less influenced than G.16, M.26 and MM.106. A bulk density of 1. 5 caused a decrease in dry weight of shoots, leaves, and roots of trees on all rootstocks. Compacted soil resulted in a decrease in leaf concentration of K and B and an increase in Mg and Mn.
In 1987, `Smoothee Golden Delicious' (`Smoothee') and `Lawspur Rome Beauty' (`Lawspur') apple (Malus domestica Borkh,) trees were planted and trained as central leaders or palmette leaders on M.7 and Mark rootstocks or were planted as slender spindles on Mark rootstocks. `Smoothee' trees were larger and had consistently greater yields and production per unit trunk cross-sectional area (TCA) than `Lawspur' trees. Slender spindle trees had lower early yields per tree and TCA but had greater cumulative yields per hectare than trees in the other training systems. In the fifth and sixth growing seasons, `Smoothee' trained as palmette leaders tended to have higher yields per hectare then central leader trees. Training system had little influence on `Lawspur' tree yields. Limb bending in 1989 increased flower density in 1989 and 1990. Cumulative yield per hectare increased 11% as a result of limb bending of trees on Mark rootstock, but bending had no influence on trees on M.7 rootstock. `Smoothee' on Mark had higher cumulative yields per hectare with the palmette leader and central leader than either `Smoothee' on M.7 in either training system or any combination with `Lawspur'.
The problem of controlling tree growth, although existing throughout the history of fruit growing, has become more acute as economic conditions and population spread force growers to become more efficient and produce more fruit on each hectare of orchard land. In 1984, a workshop (9) was organized to address this issue and the High Density Plantings Working Group has organized three successful symposia (29, 30, 31) that have reported many studies on methods to increase efficiency.
Root-pruning young greenhouse-grown MM.111 apple trees decreased leaves per tree, total leaf area, and dry weight of leaves, shoots, and roots. Root pruning had no influence on the carbohydrate fractions in the leaves or shoots, but caused an increase in soluble and insoluble fractions in the roots. No interaction occurred between root pruning and number of trees in the container. As number of trees per container increased, leaf, shoot, and total dry weight per plant decreased. Root pruning decreased shoot growth for 3 weeks after root pruning, with a return to the unpruned shoot growth rate in the 4th week. Photosynthesis and transpiration were reduced by root pruning, but not affected by tree density.
In 1981, four apple cultivars were established as a low trellis hedgerow on M.9 or free-standing central leaders on M.7 at the recommended or half the recommended spacing with the close planted trees either root pruned annually at bloom or hedged in August. Planting at half the spacing and annual summer hedging 2 sides decreased TCA 25% and canopy volume 51% with no effect on shoot growth, while annual root pruning decreased TCA 34%, canopy volume 50% and shoot length 25%. Planting at half spacing and either hedging or root pruning reduced yields per tree. Efficiency as measured by yield TCA was decreased by hedging and as measured by yield/m3 canopy volume was increased by both treatments with hedging having the greatest effect. The cumulative yield/ha was increased by both hedging and root pruning with no difference between them. Fruit size was decreased by close planting and root pruning caused a greater decrease than hedging. Close planting increased the number of spurs and shoots and LAI per unit volume of canopy with no difference between hedging or root pruning. `Empire' outproduced `Smoothee' and `Delicious' on the trellis and `Lawspur' had higher yields than any other cultivar in the central leader.
The canopy development and yield efficiency of ‘Golden Delicious’ apple trees (Malus domestica Borkh.) were measured during the sixth growing season for slender spindle (2151 trees/ha), trellis (1121 trees/ha), interstem hedgerow (795 trees/ha), and pyramid hedgerow (425 tree/ha) management systems. Pyramid hedgerow trees had the greatest trunk circumference, height, spread, and canopy volume/tree, but had a lower canopy volume/ha than the slender spindle or trellis. About 20% of the canopy of all 4 systems was present at bloom in May, 90% in June, and the maximum in July. Spur leaves followed the development pattern of the whole canopy but shoot leaf area did not reach its maximum until August. Interstem hedgerow trees had the most open canopy with the lowest amount of leaf area/unit of canopy height and the greatest amount of light penetration in the canopy. The pyramid hedgerow had a higher LAI than other systems and the increase in light in the upper third of the tree was not as great as the other systems. Trellis trees had the greatest number of fruit/100 cm2 area of both spur and shoot leaves and also the highest yield/unit trunk cross section of the 4 systems. The upper third of the canopy of all systems had the largest number of flowers and fruit, greatest amount of fruit/100 cm2 of leaf area and more light than the mid- and lower-thirds. Cumulative yield/ha and canopy volume/ha were closely related to number of trees/ha but the trellis and interstem system had a greater density of fruit/m2 of canopy than the slender spindle or pyramid hedgerow systems.
`Jonathan'/M.26 apple (Malus domestics Borkh.) trees were root-pruned annually on two sides, 60 cm from the trunk, to a depth of 40 cm for 6 years while dormant, at bloom, or in mid-June. Root pruning reduced terminal shoot growth by ≈30% in 1985-89 with no influence in 1990. Cumulative yield was reduced by root pruning at bloom (14%) or mid-June (20%), and cumulative yield efficiency [kg·cm-2 trunk cross-sectional area) was reduced by root pruning with no difference among pruning times except in 1 year, where abundant moisture throughout the season appeared to negate the effect. The intensity of biennial bearing was reduced by root pruning with no relationships to time of pruning. Root pruning resulted in a decrease in large fruit and an increase in small fruit in 3 of the 6 years. A covariant analysis with yield showed that root pruning reduced average fruit size. Root-pruned trees produced firmer fruit with an increased soluble solids concentration and had less preharvest drop than nonpruned trees. Under severe drought conditions in 1988, root pruning reduced net photosynthesis and transpiration; supplemental water (57 liters·week-1) increased transpiration and fruit size at harvest.