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Jim Syvertsen, J. Lloyd, and G. D. Farquhar

Four to six-yr-old `Red Ruby' grapefruit trees on either `Volkamer' lemon (VL) or sour orange (SO) rootstocks were fertilized with 3 rates of nitrogen (N) over a 3 year period. We studied the effects of leaf N concentration on stomatal conductance (gs), net assimilation (A) of CO2 (Li-Cor portable gas exchange system), carbon isotope discrimination (δ 13C) of tree tissues, root growth, canopy development and fruit yield. Using springtime measurements of net gas exchange during the fifth year, gs, A and leaf tissue δ 13C were positively correlated with leaf N. The faster growing trees on VL had larger canopy volumes and fruit yields but lower leaf N, A and δ 13C than those on SO. Thus δ 13C was positively correlated with A but negatively related to tree size and yield. By the sixth year, δ 13C was still related to N but tree growth had apparently obscured any rootstock effects on leaf N, water use efficiency, A and δ 13C. Leaf and trunk bark tissue δ 13C did not differ but root bark had lowest δ 13C regardless of rootstock species.

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Xinwang Wang, Deborah Dean, Phillip Wadl, Denita Hadziabdic, Brian Scheffler, Timothy Rinehart, Raul Cabrera, and Robert Trigiano

Lagerstroemia L. (crape myrtle) is an economically important woody plant genus with several deciduous flowering ornamental species. A wide range of flower colors, long flowering periods, growth habits ranging from miniature to tree sizes, and exfoliating bark characteristics provide horticulturists and nursery growers with a great deal of interest in the breeding and genetics of this genus. We report microsatellite marker development from a GT-enriched genomic library of the interspecific hybrid ‘Natchez’ (L. indica L. × L. fauriei Koehne). Twelve of 43 novel microsatellite loci were characterized on a collection of 33 Lagerstroemia cultivars and accessions. Four to eight alleles per locus (mean = 5.6 alleles) were detected. Allelic richness ranged from 3.9 to 7.2 with a mean of 5.3. The level of polymorphism detected (average gene diversity of 0.68) indicates moderately high genetic diversity within the selections of crape myrtle cultivars and accessions. The examined markers also exhibited high cross-species transferability to L. fauriei, L. limii Merr., and L. subcostata Koehne.

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Jeffrey F. Derr

The tolerance of newly planted apple (Malus domestica Borkh.) and peach [Prunus persica (L.) Batsch] trees to the postemergence herbicide triclopyr was evaluated infield trials. Apple and peach trees were not injured by triclopyr applied at rates ranging from 0.28 to 1.12 kg acid equivalent (a.e.)/ha as a directed spray to soil. No injury was observed following direct application of 10 ml of a triclopyr solution at 2 g a.e./liter to the lower bark of either tree species. Applications of that solution to an individual branch injured or killed the treated apple or peach branch but did not affect the rest of the tree. No reduction in tree growth or injury was noted 1 year after triclopyr application. Applications of 10 ml of a glyphosate solution at 15 g a.i./liter to an apple branch caused severe injury and a growth reduction by 1 year after application, and killed all treated peach trees when applied to one branch. No triclopyr or 2,4-D treatment had affected apple or peach trunk diameter, number of branches, or tree size 1 year after application. Chemical names used: N-(phosphonomethyl)glycine (glyphosate); [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid (triclopyr); (2,4-dichlorophenoxy)acetic acid (2,4-D).

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R.E. Byers, D.H. Carbaugh, and L.D. Combs

`Fuji'/MM.111, `Pink Lady'/M.7A, and `Summerfield'/M.7A apple trees were planted in several types of individual root restrictive bags in the field in 1995. Bags were made of Knit and Woven fabrics, Galvanize hardware cloth (6.4 cm) with various holes sizes and of different bag volumes. The bags confined the development of large roots to within the bag. Roots that penetrated the bag resulted in root branching and large root inhibition. As the roots enlarged, roots penetrating the bags were restricted in diameter by the fabric hole size. Roots enlarged to some degree on both sides of the fabric holes but were not killed by girdling within the first few years. Root restriction bags decreased trunk caliper, shoot growth, pruning weights, number of cuts per tree, increased flowering, fruit numbers, and weight per tree. Fruit firmness, soluble solids and color was increased and starch was lower than the nonbagged controls. In cage and tank trials pine and/or meadow voles easily penetrated all of the fabric and polypropylene bags within 24 h, except for the galvanized hardware cloth (6.4 cm). Susceptibility of each material to vole damage was tested by placement of an apple inside a small bag of each. Root restriction bags seemed to be a viable alternative to dwarfing rootstocks for control of tree size, early flowering, and early fruiting.

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George M. Greene II and Alvan G. Gaus

The influence of rootstocks on the growth and productivity of `Starkspur Supreme Pagnelli Delicious' was determined in an NC-140 experiment started in 1984. The planting was supplemental to the main experiment and it contained Ottawa (Ott) 3, M.20, and Arnold Lynd (AL) 800, but did not contain Budagovsky (Bud) 490, Bud 9, Antonovka 313, or C6. Trees that apparently would not stand were given support. Data on tree size and yield were collected every year. As expected, many characteristics were strongly influenced by rootstock. Yield efficiency calculated as the total fruit weight per square cm of trunk cross-sectional area was used as a measure of production efficiency. In 1989, efficient producers of fruit (all in decreasing order) were Poland (P) 2, EMLA.26, P 16, and Michigan Apple Clone (MAC) 39. Intermediate in productivity were M.20, Cornell-Geneva (CG) 10, Pl, and AL 800. A lower efficiency group of rootstocks were EMLA.7, Ott 3, MAC 1, Seedling, M.4, P 18, and CG 24. `Golden Delicious' and `McIntosh' on EMLA.26, used as pollinizers, were ranked second and third in yield efficiency.

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Victor Medina-Urrutia, Karla Fabiola, Lopez Madera, Patricia Serrano, G. Ananthakrishnan, Jude W. Grosser, and Wenwu Guo

No presently available rootstock combines all the available rootstock attributes necessary for efficient long-term citriculture (production and harvesting) of Mexican limes and other commercially important scions. In the present study, somatic hybridization techniques were used to combine the widely adapted Amblycarpa mandarin (also known as Nasnaran mandarin) with six different trifoliate/trifoliate hybrid selections: Benton, Carrizo, and C-35 citranges; Flying Dragon and Rubidoux trifoliate oranges; and a somatic hybrid of sour orange + Flying Dragon. The ultimate goal of this research is to generate polyploid somatic hybrids that express the complementary horticultural and disease resistance attributes of the corresponding parents, and have direct potential as improved tree-size controlling rootstocks. Somatic hybrids from all six parental combinations were confirmed by a combination of leaf morphology, flow cytometry, and randomly amplified polymorphic DNA (RAPD) (for nuclear hybridity) and cleaved amplified polymorphic sequence (CAPS) analyses (for mtDNA and cpDNA). This is the first report of citrus somatic hybridization using Amblycarpa mandarin. Unexpected hexaploid somatic hybrid plants were recovered from the fusion of Amblycarpa mandarin + C-35 citrange. Hexaploid hybrids should be very dwarfing and may have potential for producing potted ornamental citrus. Resulting somatic hybrid plants from all six combinations have been propagated by tissue culture and/or rooted cuttings and are being prepared for commercial field evaluation for their potential as improved rootstocks for Mexican lime and other important scions.

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Cheryl R. Hampson, Harvey A. Quamme, Frank Kappel, and Robert T. Brownlee

The effect of increasing planting density at constant rectangularity on the vegetative growth and light interception of apple [Malus ×sylvestris (L) var. domestica (Borkh.) Mansf.] trees in three training systems (slender spindle, tall spindle, and Geneva Y trellis) was assessed for 10 years. Five tree densities (from 1125 to 3226 trees/ha) and two cultivars (Royal Gala and Summerland McIntosh) were tested in a fully guarded split-split plot design. Planting density was the most influential factor. As tree density increased, tree size decreased, and leaf area index and light interception increased. A planting density between 1800 and 2200 trees/ha (depending on training system) was needed to achieve at least 50% light interception under the conditions of this trial. Training system altered tree height and canopy diameter, but not total scion weight. Training system began to influence light interception in the sixth leaf, when the Y trellis system intercepted more light than either spindle form. Trees trained to the Y trellis tended to have more spurs and a lower proportion of total leaf area in shoot leaves than the other two systems. The slender and tall spindles were similar in most aspects of performance. Tall spindles did not intercept more light than slender spindles. `Royal Gala' and `Summerland McIntosh' trees intercepted about the same amount of light. `Royal Gala' had greater spur leaf area per tree than `Summerland McIntosh', but the cultivars were similar in shoot leaf area per tree and spur density.

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Richard S. Buker*, Jackie K. Burns, and Fritz M. Roka

Continuous canopy shakers (CCS) were developed in the late 90's and have been used to commercially harvest citrus in Florida. A viable mechanical harvester in Florida must be able to selectively remove mature `Valencia' fruit. A study was conducted to evaluate the effect of operating conditions on mature and immature fruit removal during the 2003 harvest season. The study was conducted in the southern flat woods and northern ridge areas. The study treatments were completely random and replicated four times. The CCS treatments were 145, 215, 230, and 245 cycles per minute (cpm) and a hand picked control. The harvest occurred on 17 and 19 June at the southern and northern sites, respectively. Mature fruit removal linearly increased from 95.7% to 97.9% between 145 and 245 cpm, respectively. Varying the operating ranges significantly influenced mature fruit removal in the southern flat woods site. The trees at the southern site were taller (>4m), and had a larger crop load. At the northern ridge site where trees were smaller, varying the CCS operating ranges did not significantly influence mature fruit removal. Immature fruit removal was influenced by the operating ranges. Immature fruit removal was increased at least 22% over hand picked controls. The results were interpreted to indicate the frequency of CCS is dependent on tree size. The initial selectivity of the CCS was not equal to hand picking.

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Wesley R. Autio, Duane W. Greene, and William J. Lord

`Summerland Red McIntosh' apple trees (Malus domestica Borkh.) on M.9/A.2, O.3, M.7 EMLA, M.26 EMLA, M.7A, OAR1, and Mark were evaluated over 10 years. Trees on M.7 EMLA and OAR1 were the largest, and trees on Mark were the smallest. Trees on M.7 EMLA produced the highest yields per tree, and those on OAR1 and Mark produced the lowest. The most yield-efficient trees were on O.3 and Mark. The least efficient trees were on OAR1. Fruit from trees on O.3, M.26 EMLA, or M.9/A.2 generally were the largest, and fruit from trees on OAR1 generally were the smallest. Red pigment development was inversely proportional to canopy size, with Mark resulting generally in the most red pigmentation and M.7 EMLA and M.7A generally resulting in the least. Methods of presenting productivity were compared. Presentation of yield per land area occupied or projected yield per planted area were biased in experiments where only some trees naturally would exceed the allotted space and, therefore, were containment pruned and where tree-to-tree competition was directly proportional to tree size. Yield efficiency was a less biased estimate. Further, in single-row planting systems with trees spaced at optimal densities, small trees must be more efficient than large trees to obtain similar yields.

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H. Khemira, L.E. Schrader, F.J. Peryea, R. Kammereck, and R. Burrows

One-year-old `Fuji' apple trees on six rootstocks (Mark, M.9, M.26, M.7A, MM.106, and MM.111) were compared for N and water uptake and utilization. The trees were potted in sand and subjected to a 75-day N-deprivation period (supplied with modified Hoagland's solution lacking N) to deplete their N reserves. Thereafter, they were supplied with a complete modified Hoagland's solution. Uptake of water and N differed by rootstock. Water and N uptake were positively related to tree dry weight (r = +0.97, P = 0.001). Trees that had the highest N concentrations at planting were the last to set bud during the N-deprivation-phase. Tree size after one growing season depended largely on rootstock girth and whole-tree-Nconcentration at planting (r 2 = 0.80, P = 0.0001) regardless of rootstock. Water and N uptake efficiency (liter of water or mg N absorbed per g root dry weight, respectively) differed among the rootstocks, being highest for trees on MM.111 and lowest for trees on M.7A rootstock. Nitrogen and water utilization efficiency (g dry weight gained per mg N or per liter of water absorbed, respectively) were not influenced by the rootstock.