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Paul J.R. Cronjé, Gerard Jacobs and Nigel C. Cook

Two-year-old apple branches, ≈50 cm long, were selected from a commercial `Royal Gala' orchard in the Ceres (Koue Bokkeveld) region of the Western Cape, South Africa [33 °S, 945 m, 1500 Utah model chilling units (CU)]. In 2000, the branches received either cold storage at 5 to 7 °C or natural chilling in the field. In 2001, the trial was repeated, but only with field chilling. The branches received five dormant pruning treatments: control (not pruned); pruning back to the fourth lateral shoot (heading) before or after chilling; and removal of the second and third lateral shoots (thinning) before or after chilling. After pruning and chilling, the branches were removed from the orchard or cold room every 2 weeks and forced in a growth chamber at 25 °C. The rate of budburst (1/days to budburst) was determined for the terminal buds of the lateral shoots. Lateral shoots on the 2-year-old branches were categorized according to position: the most distal extension shoot, and all other laterals grouped. Removing distal tissue by pruning (heading more than thinning) enhanced the effect of chilling on the terminal buds on the lateral shoots and promoted budburst. Pruning was more effective before than after chilling. Pruning enhanced the growth potential of the terminal buds on proximal shoots on 2-year-old branches.

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Charlotte M. Guimond, Gregory A. Lang and Preston K. Andrews

To examine the effect of timing and severity of summer pruning on flower bud initiation and vegetative growth, 4-year-old `Bing' cherry trees (Prunus avium L.) were pruned at 31, 34, 37, 38, or 45 days after full bloom (DAFB) with heading cuts 20 cm from the base of current-season lateral shoot growth, or at 38 DAFB by heading current-season lateral shoot growth at 15, 20, 25, or 30 cm from the base of the shoot. The influence of heading cut position between nodes also was examined by cutting at a point (≈20 cm from the shoot base) just above or below a node, or in the middle of an internode. Summer pruning influenced the number of both flower buds and lateral shoots subsequently formed on the shoots. All of the timings and pruning lengths significantly increased the number of both flower buds and lateral shoots, but differences between pruning times were not significant. There was significantly less regrowth when shoots were pruned just below a node or in the center of an internode, rather than just above a node, suggesting that the length of the remaining stub may inhibit regrowth somewhat. The coefficient of determination (r 2) between flower bud number and regrowth ranged from -0.34 to -0.45. In young high-density sweet cherry plantings, summer pruning may be useful for increasing flower bud formation on current-season shoots. The time of pruning, length of the shoots after pruning, and location of the pruning cut can influence subsequent flower bud formation and vegetative regrowth.

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Shiow Y. Wang and Miklos Faust

The activity of ascorbic acid oxidase (AAO) was studied in apple (Malus domestica Borkh.) buds during dormancy and thidiazuron-induced budbreak. In dormant buds, activity of AAO was low compared with buds that were treated with thidiazuron and had resumed growth. An increase in AAO activity began at the time of metabolic transition from dormancy to budbreak. The highest level of activity was reached 10 days after thidiazuron induction during the expansion growth phase. In vitro AAO activity of apple bud extract was increased by addition of Cu (CuSO) and inhibited by Cu-chelating agents, diethyldithiocarbamate (DDC), sodium azide (NaN), and 8-hydroxyquinoiine (8-OH-Q). In vivo treatment of apple buds with Cu-chelating agents inhibited AAO activity and bud growth but not budbreak. Chemical name used: N- phenyl -N' -1,2,3-thidiazol-5-ylurea (thidiazuron).

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Jorge H. Siller-Cepeda, Leslie H. Fuchigami and Tony H.H. Chen

The effects of hydrogen cyanamide (H2CN2) on budbreak and phytotoxicity of l-year-old potted peach trees [Prunus persica (L.) Batsch. cv. Redhaven] over a wide range of concentrations at several stages of dormancy were studied. Endodormancy (180° GS; degree growth stage) began on 1 Oct. Maximum intensity of endodormancy (270° GS) was reached after the plants were exposed to 320 chill units on 1 Nov., and 50% of the buds were broken at 860 chill units on 1 Dec. Five concentrations of H2C N2 (0, 0.125, 0.25, 0.5, and 1.0 m) were applied on 1 and 15 Oct., 1 and 15 Nov., and 1 and 15 Dec. 1990. All concentrations promoted budbreak; however, percent budbreak and phytotoxicity depended on concentration and timing of application. The most effective concentration (greatest budbreak and lowest phytotoxicity) was 0.125 m H2CN2 on all treatment dates. Phytotoxicity was evident at all application dates but was greatest at the highest concentrations. Plants were most resistant to H2CN2 at maximum intensity of endodormancy. Hydrogen cyanamide-induced budbreak was highest during the later stages of endodormancy (295 to 315° GS). Treatments applied during the ecodormancy stage (340° GS) inhibited and delayed budbreak and damaged buds and stems. Chemical name used: hydrogen cyanamide (H2CN2, Dormex).

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Chenq-chu Nee

The purpose of this invention is to preserve the germplasm which are compatibly graftable for each other in the specific environment. The preserved [interstock] is protected by the rootstock which is used to the stresses from underground, and the “topstock” which is tolerant to the stresses from aboveground.

The compound plant (Top-interstock-rootstock) is different from the traditional combinations which the interstock impove the impatibility between scion and rootstock. The interstock in this design must be compatible with its top and rootstock parts and keep “paradormancy” in the germplasm repository.

Preservation of pear species & cultivars will be presented to describe the details of the techinque.

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Dehua Liu, Miklos Faust, Helen A. Norman, Merle Millard and Garry W. Stutte

Membrane lipids and cellular water states were studied in endodormant and paradormant apple buds. Paradormancy was overcome by thidiazuron while endodormant buds were forced to break after a certain period of chilling. Nuclear magnetic resonance imaging was used to determine water states in buds of different stages of dormancy. In endodormant buds, the changes in water states from a more tightly-bound to a more free form were correlated with changes in membrane fatty acid composition. The ratio of saturated/unsaturated fatty acids decreased with chilling, especially in C18:l/C18:3 molecular species of phosphatidylcholine and phosphatidylethanolamine. Bud lipase activity, which was assayed by in vitro hydrolysis of triglycerides, showed an abrupt increase after chilling treatments.

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Shiow Y. Wang, Miklos Faust and Michael J. Line

The effect of Indole-3-acetic acid (IAA) on apical dominance in apple (Malus domestica Borkh.) buds was examined by studying changes In proton density (free water) and membrane lipid composition in lateral buds. Decapitation induced budbreak and enhanced lateral bud growth. IAA replaced apical control of lateral bud paradormancy. Maximal inhibition was obtained when IAA was applied immediately after the apical bud was removed. Delaying this application weakens the effect of IAA. An increase in proton density in lateral buds was observable 2 days after decapitation, whereas the change in membrane lipid composition occurred 4 days later. Decapitating the terminal bud induced an increase in membrane galacto- and phospholipids. and the ratio of unsaturated to corresponding saturated fatty acids. Decapitation also induced a decrease in the ratio of free sterols to phospholipids in lateral buds. Application of IAA to the terminal end of decapitated shoots inhibited the increase of proton density and prevented changes in the membrane lipid composition of lateral buds.

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L.H. Fuchigami and M. Wisniewski

The purpose of this presentation is to discuss the value of identifying growth stages of bud dormancy numerically. The Degree Growth Stage Model (°GS Model) will be used to quantify the annual growth stages and the various developmental stages of endo-, eco-, and paradormancy. The model is divided into 360°GS's, illustrated either as a sine curve or a circle, that serve as a timeline for the cyclical passage of temperate woody plants, through five distinct point events (growth stages). The sine curve illustrates the relative degree of development of the segment events between the point events. This paper will focus on the °GS model as a relative method of quantifying the various segment events and improving our communication of the annual physiological processes of temperate woody plants. In addition, recent evidence on altering dormancy, and its impact on dormancy models, will be presented.

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Shiow Y. Wang and Miklos Faust

The ability of low and high temperatures to overcome endo- and paradormancy along with the possible mechanisms involved in these treatments for breaking apple (Malus domestica Borkh. `Anna') bud dormancy were studied. All these treatments induced budbreak in paradormant (in July) and endodormant (in October) buds. Cold and heat treatments increased ascorbic acid, the reduced the form of glutathione (GSH), total glutathione, total non-protein thiol and non-glutathione thiol, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased. The treatments also increased the ascorbic acid: dehydroascorbate and GSH: GSSG ratios and the activity of ascorbate-free radical reductase, ascorbate peroxidase, dehydroascorbate reductase, ascorbate oxidase, and glutathione reductase in the buds. These results indicate that budbreak induced by cold and heat treatments is associated with the removal of free radicals through activated peroxide-scavenging systems.

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James A. Schrader and William R. Graves

The genus Dirca L. (Thymelaeaceae) consists of three species of understory shrubs. Dirca palustris L. is sparsely distributed across eastern North America, D. occidentalis Gray is endemic near the San Francisco Bay, and D. mexicana Nesom & Mayfield is known only in one population in northeastern Mexico. Despite interest in the horticultural use of Dirca, plants seldom are marketed. Difficult propagation impedes production of Dirca. We sought to define protocols that promote uniform seed germination of all three Dirca spp. Endodormancy and paradormancy cause sporadic germination over several years under natural conditions, but endocarp removal, cold stratification, and treatment with GA3 increased germination percentage, speed, and uniformity. Dirca occidentalis was most responsive; up to 94% of seeds germinated after endocarp removal, 24 hours in GA3 at 50 mg·L–1, and stratification at 4 °C for 30 days. Treatments also were effective for D. palustris (up to 68% germination), but seeds of D. mexicana were unresponsive and germinated at 25% or less. Seed treatments should facilitate production of D. occidentalis and D. palustris, but further research is needed to define methods to propagate D. mexicana for horticultural use and for conserving this rare species in the wild.