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Richard E.C. Layne and Perry Y. Jui

Ten genetically diverse peach [Prunus persica (L.) Batsch] seedling rootstocks were studied for 10 years on Fox sand using `Redhaven' as the scion. The purpose of the experiment was to assess the performance of three Harrow Research Station (Ont.) hybrid selections (H7338013, H7338016, and H7338019) and two northern China introductions (`Chui Lum Tao' and `Tzim Pee Tao') against five commercial standards, two of which were selected in Canada (`Harrow Blood' and `Siberian C') and three in the United States (`Bailey', `Halford', and `Lovell'). Rootstock performance was assessed indirectly by measuring or subjectively rating various aspects of scion performance including annual trunk cross-sectional area (TCA); final tree height, spread, and TCA; bloom and fruit set intensity; yield and yield efficiency; canker (Leucostoma spp.) severity; defoliation rate; winter injury; cold hardiness of flower buds and shoot xylem; and tree survival. Rootstock effects on the above measurements and ratings were significant in some years and not in others. Year effects were always large and significant, while rootstock × year interactions were usually small and not significant. In the combined analyses over years, the largest rootstock effects were obtained for bloom, fruit set, and defoliation ratings and for TCA measurements. Three cumulative responses, including marketable yields, yield efficiency, and tree survival, were used for comparing the five experimental rootstocks with the five commercial standards and also for ranking the 10 rootstocks with respect to each other to assess their potential commercial value as peach rootstocks. `Chui Lum Tao', H7338013, and `Bailey' had the most commercial potential for southern Ontario because they typically promoted above average cumulative yield, yield efficiency, and tree survival. `Tzim Pee Tao', `Siberian C', and `Harrow Blood' were less valuable, with low cumulative marketable yields. `Halford' and `Lovell' were the least valuable, with the lowest tree survival (17%). Performance of H7338013 exceeded that of both parents (`Bailey' and `Siberian C'), H7338019 exceeded `Siberian C' but not `Bailey', while performance of H7338016 was inferior to both parents. Wider testing of the experimental rootstocks on different soil types and climatic zones is needed.

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C. A. Mullins and R. A. Straw

Nine size controlling apple rootstock were evaluated in trials initiated at the Plateau Experiment Station, Crossville, TN in 1981 using `Starkspur Supreme Delicious' as the scion cultivar. Tree survival was poor with M.9 EMLA, Ottawa 3, M.27 EMLA, and Mark rootstock. Trees on M.27 EMLA and Mark were extremely low in vigor and yields. Root suckering was severe with MAC 24 and M.7 EMLA. Trees on M.26 EMLA were the most productive over six fruiting years. Fruit from trees on Ottawa 3 tended to be firmer and have more red color than fruit from trees on the other rootstock when harvested on the same date. Fruit size did not vary due to rootstock over the six fruiting years.

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G.E. Boyhan, J.D. Norton, and J.A. Pitts

The dwarfing characteristics of St. Julien and Pixy rootstocks, measured by shoot growth, were evident with `AU-Amber' and `AU-Producer' plum (Prunus salicina Lindl.) scions. Dwarfing did not occur with `AU-Rubrum'. Trunk cross-sectional area (TCA) was reduced with `AU-Amber', `AU-Producer', and `AU-Rubrum' scions on St. Julien and Pixy rootstocks. After 3 years, tree survival was 94% for Lovell; 89%, Halford; 57%, Nemaguard; 75%, Nemared; 83%, St. Julien; and 47%, Pixy. Tree survivability was significantly lower on Nemaguard and Pixy rootstocks than on Lovell and Halford. Multiple regression of total shoot growth, TCA, and survivability against foliar nutrient content resulted in the following significant equations: 0.460Mg - 0.210Mn, 0.236B - 0.487Mn, and 0.359N + 0.398Ca - 0.267P - 0.360Fe for each, respectively. Growth, survivability, and foliar nutrient content are significantly affected by rootstock in plum production.

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George Yelenosky

Potted greenhouse-grown, l-year-old `Hamlin' orange [Citrus sinensis (L.) Osbeck] trees on 1.5-year-old rough lemon (C. jambhiri Lush.) rootstock were temperature-conditioned for 6 consecutive weeks in a controlled-environment room to test cold-hardening ability. Holding at 15.6 ± 0.6C during 12-hr days [425 μmol·s-1·m-2 photosynthetic photon flux (PPF) at top of trees] and 4.4C during nights resulted in 100% tree survival and no leaf loss “after 4 hr of – 6.7C in a dark freeze test room. Unhardened greenhouse trees were killed to rootstock. Solute efflux (dS·m-1) from unhardened frozen leaves was > 20-fold that from frozen leaves on hardened trees and nonfrozen leaves on unhardened trees. Oxygen uptake was not significantly impaired in frozen hardened leaves. No 02 uptake was evident for frozen unhardened leaves.

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Kim D. Bowman

Bending was compared to cutting off for effectiveness in forcing growth of sweet orange and mandarin scions budded on `Carrizo' citrange, `Swingle' citrumelo, and 17 new hybrid citrumelo rootstocks. For both scion types, more than twice as many plants from the bending treatment than the cut treatment had growing scion buds at 12 weeks. This advantage of the bending treatment was similar for most scion/rootstock combinations except with sweet orange scion on `Carrizo', which produced outstanding bud growth from both forcing methods. Length of growing shoots at 12 weeks was >14 times longer from the bending than the cut treatment for both scions and with all rootstocks. Tree survival and yield of usable trees at 35 weeks old were also significantly better for the bending treatment than for the cut treatment. There was an overwhelming advantage to using the bending treatment instead of cutting off in forcing scion bud growth for propagating citrus trees on citrumelo rootstocks.

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Bruce W. Wood

Pecan [Carya illinoinensis (Wangenh.) K. Koch] nursery transplants performed best on establishment in nonirrigated orchards when using large trees planted early in the dormant season. After 6 years, growth and survival of bare-root transplants were equal to that of containerized transplants when established during the dormant season. Reducing transplant trunk height by ≤75% at planting did not affect subsequent tree survival, although rate of height growth and tree vigor increased such that there was no difference between pruned and nonpruned trees after 3 years, except that pruned trees appeared to possess greater vigor. There also were no differences in growth or survival between augured and subsoil + augured planting sites within 6 years of transplanting, and there were no differences between root pruned (severe tap or lateral root pruning) and nonpruned trees.

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Mark W. Jarecki, David J. Williams, and Gary J. Kling

Growers, nurseries, landscape contractors and installers, and those responsible for maintenance have observed a trend that trees are too deep within the root ball. This study addresses the relationship between planting depth and its effect on tree survival, root growth, root architecture, and caliper growth. The experiment was initiated to determine the effect of planting depth on nursery-grown trees. Three-year-old, 2.1–2.7 m, bare-root liners of Acer platanoides `Emerald Lustre', Fraxinus americana `Autumn Purple', Fraxinus pennsylvanica `Patmore', and Gleditsia triacanthos f. inermis `Shade Master' were planted in April 2004 in a completely randomized design with 20 replications per treatment per species. The trees were selected so that the distance between the graft union and the trunk flare was consistent. Trees were planted with the graft union 15.2 cm below the soil surface, or with the base of the graft union at the finished grade or with the trunk flare at the finished grade. The trees were grown in a nursery field setting with minimal supplemental watering. There were no differences in stem caliper growth at the end of two seasons in any of the four species. Root dry mass, stem elongation, and rooting structure were determined on a representative sample of trees while others were planted into the landscape for a long-term study of the effects of the original planting depth on landscape performance.

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Gregory L. Reighard, David R. Ouellette, and Kathy H. Brock

A field planting of 18 selections and 10 named cultivars of pawpaw (Asimina triloba) was established in November 1996 near Clemson, S.C., as part of the Pawpaw Regional Variety Trial coordinated by Kentucky State University. Trees were planted at 2.0 × 5.5 m spacing with drip irrigation and straw mulch in a randomized complete block design consisting of 8 single-tree replications. Data collected through 2005 included tree survival, total tree yield, and yield and average weight of fruit weighing >150 g. Since the start of the trial, 3 selections, 1-7-1, 11-5 and 8-58 have been named and released as `Shenandoah', `Susquehanna' and `Rappahannock', respectively. The highest yielding cultivars were `Shenandoah', `Rappahannock', and `PA-Golden'. The cultivars with the largest percentage of large fruit were `Shenandoah' and `Susquehanna'. `Middletown', `Mitchell', `Rappahannock', `Taytwo', `Wells' and `Wilson' produced the largest percentage of small fruit (<150 g). After 9 years, 66% of the original trees (i.e., scions) were alive. `Rappahannock', `PA-Golden', `Sunflower' and `Wilson' had either one or zero trees die, whereas `Middleton' and `Wells' had only 2 trees alive. Among the selections, 2-54, 9-58, 11-13, 1-68, 3-11, and 8–20 had either 88% or 100% survival. The highest yielding selections were 10-35, 1-7-2, 1-68, and 2-10, and 1-7-2, 2-10, 4-2, and 5-5 produced the highest percent of large fruit. Fruit quality characters such as aroma, flavor, aftertaste and texture were not quantified or evaluated.

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Wayne J. Bourgeois and Alvin J. Adams

During the 1989 freeze, a scaffold branch irrigation freeze protection system was in operation on five-year old `Washington' navel and `Owari' satsuma trees and several younger trees of various navel orange varieties, a cold tolerant satsuma selection and other navel orange trees. Temperature dipped to a low of -11.1C, with 20 consecutive hours of -6.7C or below and 80 consecutive hours of 0C or lower. Post freeze evaluations and ratings show that an average tree survival rate of 94.6% was obtained. An average of 84.6% survival of scaffold branches and an average of 11% canopy survival was also achieved through the use of scaffold branch irrigation for freeze protection. Trunk injury ratings averaged 8.8 (scale 0-10; 0 – dead, 10 – no injury) and shoot regrowth after pruning dead wood averaged 8.0 (scale 0-10; 0 – no shoot regrowth, 10 – excellent shoot regrowth. The average percentage of the regrowth was slightly above 80% of the original tree volume prior to the freeze. Nonprotected trees sustained 100% kill and necessitated removal and reestablishment.

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Robert C. Ebel, Bryan Wilkins, David Himelrick, Tom Beckman, Andy Nyczepir, and Jim Pitts

Twelve peach rootstocks including `Lovell', `Nemaguard', `Flordaguard', `14DR51', five `Guardian' (BY520-9) selections, and three BY520-8 selections, were evaluated under field conditions to determine their effect on performance of `Cresthaven' peach. The trees were planted in 1994. Trunk cross-sectional area of BY520-8 selections SL1923 and SL4028 was 28% larger than the rest of the rootstocks, which were similar. There was no crop in 1996 due to late spring frost. Yield in 1997 and 1998 was higher for SL1923 because of higher cropload than the rest of the rootstocks, which were similar. Yield efficiency varied across years and rootstocks. Fruit weight varied among rootstocks but all were commercially acceptable. Harvest date was advanced by two days for some rootstocks compared to Lovell and none were delayed. Percent red blush, soluble solids and firmness varied among rootstocks, but none demonstrated superior quality in all of these parameters as compared to Lovell. Ring nematode population densities were above the threshhold considered to be critical for onset of PTSL for all rootstocks in 1997 and 1998. Tree survival was at or above 86% for all rootstocks and death was not correlated with ring nematode density No trees developed symptoms characteristic of Peach Tree Short Life disease complex. Guardian selections performed adequately compared to the commonly used commercial rootstocks in this study, however, the yield date are from 2 years only.