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  • Author or Editor: Amnon Erez x
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The shortcomings of conventional peach orchards make it increasingly difficult for growers to cope with production problems under the prevailing economic conditions. The large tree requires a relatively high labor input due to the location of a large portion of its fruit in the upper part and the reduced fruitfulness of the lower part.

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Most of the works evaluating dormancy completion relies on measuring the level of budbreaking or the time needed for buds to break in forcing conditions. In all cases, the evaluation of budbreak is limited to the initial stages of bud opening in both vegetative and floral buds. Very rarely the response of the new growth is determined. It is accepted that dormancy completion of the bud is of a qualitative nature of yes or no. This reasoning led to using excised branches that can not support normally a growing bud but may support the evaluation of the emerging buds. In practice, the effect of breaking bud dormancy is far reaching and has an impact on the development after budbreaking. Growth vigor is a characteristic tied to the rate of dormancy completion in a quantitative manner. After exposure to sufficient chilling growth is rapid and vigorous. When buds are exposed to warm winters, growth is sluggish and poor. Under certain conditions, budbreak may be high, but all vegetative buds will form rosettes. Likewise with floral buds, they may break satisfactorily but will not set normal fruit especially in stone fruit species. In a recent study of bud dormancy inheritance in apricots, budbreak showed a clear dominance of the low chilling characteristic; level of vegetative vigor showed a similar effect to the high and low chilling parents. Thus, two characteristics of dormancy completion should be considered. The first is the level of budbreak and the other is the vigor of the growing vegetative buds and the functionality of the flower buds, as both are affected by the conditions that induce dormancy completion.

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Interest in artificial control of budbreak of deciduous fruit trees species is closely connected with commercial attempts to grow these species in warm locations, where the chilling requirements are not fulfilled naturally. This interest developed following attempts to grow such species in warm countries that did not want to or could not import these fruits from cooler regions. In subtropical regions like the Cape zone in South Africa, eastern Australia, and Israel, the problem was more acute in the 1950s and 1960s. Adoption of low-chilling cultivars, or a shift of production to cooler, better-adapted areas, improved tree performance considerably. Nevertheless, sporadic problems after exceptionally warm winters still pose a commercial problem. In other areas, such as southeastern United States, the risk of spring frost is such that low-chilling cultivars with their early budbreak cannot be grown in northern locations, and, in such regions, chemical treatments are needed occasionally.

Open Access
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Promotion of leaf bud break in ‘Golden Delicious’ apple by a mineral oil and dinitro-o-cresol (DNOC) combination spray depended on day-time temperature. Higher temperatures during the first 2 weeks after spraying increased the level of bud break. The highest temperature tested, 30°C, most effectively promoted lateral bud break.

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Rapid propagation of the apple rootstocks Mailing Merton (MM) 104, MM 106 and MM 109 (Malus sp.) achieved was by shoot tip proliferation using a Murashige and Skoog basal medium with 1 mg/liter 6-benzylamino purine (BA) and 1 mg/liter indolebutyric acid (IBA). Improved proliferation was achieved by using a liquid medium. Two media were selected for rooting: the first contained IBA for root initiation and the second was without IBA but plus 0.25% activated charcoal for improved root development. Plantiets were successfully transferred to soil.

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Five-day-old etiolated cucumber (Cucumis sativus L. cv. Marketmore) seedlings held at 2C for 72 hours develop chilling injury resulting in desiccation and collapse of the hypocotyl tissues and eventual plant death. Hypoxia-induced accumulation of ethanol and acetaldehyde led to tolerance to subsequent chilling as evidenced by continued hypocotyl growth and freedom from injury. Arrest of volatile accumulation by applied bisulfite negated the development of hypoxia-induced chilling tolerance in seedlings. In seedlings held in normoxia, cold tolerance was induced by applied ethanol vapors, whereas acetaldehyde had a marginal effect, suggesting that hypoxia-induced cold tolerance may arise from the accumulation and activity of ethanol. Cold tolerance was induced by exposure to gaseous n-propanol and n-butanol vapors and other volatile anesthetics, including chloroform and halothane, indicating that ethanol activity may stem in part from an anesthetic effect that causes disorder of membrane lipids. However, development of cold tolerance in ethanol-enriched tissues was time-dependent, suggesting an association with biosynthetic event(s). Ethanol did not change the fatty acid composition in cucumber hypocotyl membranes.

Free access

Processed-kaolin particle films (PKPFs) are used commercially in large quantities on horticultural crops to repel insects, and reduce heat stress and solar injury of fruit. Our studies determined the effect of two processed-mineral particle film materials (kaolin and calcium carbonate), on whole plant carbon assimilation, water use efficiency, yield, mean fruit weight and quality in `Empire' apple [(Malus ×sylvestris (L.) Mill var. domestica (Borkh Mansf.))] over a four-year period. The application of a PKPF reduced canopy temperature, and probably reduced environmental stress, resulting in increased mean fruit weight and red color in two of the four years of the study. Whole canopy carbon assimilation studies indicated increased carbon assimilation only under conditions of high air temperature. The PKPF sprayed leaves also had reduced water use efficiency; likely due to increased stomatal conductance associated with reduced leaf temperature. Calcium carbonate had none of the positive effects of PKPF and reflected more photosynthetically active radiation (PAR) than the PKPF.

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The relative contribution of various temperatures to dormancy completion of lateral vegetative apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] buds was studied quantitatively on whole container-grown trees. Trees were exposed continuously to 10 different temperatures and also to daily alternating temperatures in a 24-hour cycle. In addition, fully chilled vertically and horizontally positioned shoots were compared under forcing conditions. No budbreak occurred in shoots chilled above 12.5 °C. There was a steep increase in budbreak as the chilling temperature fell from 12.5 to 7.5 °C. There was little difference in the level of budbreak on shoots chilled between 7.5 and 0 °C. The relative contribution of temperature to chilling accumulation in apple found in our study differs from what has been proposed for stone fruit and for apple in previous studies, especially at temperatures <6 °C. The length of exposure to forcing conditions required to initiate budbreak diminished as the chilling temperature was reduced. No additional bud-break was apparent on shoots chilled longer than 2100 chilling hours. The chilling requirement found here for lateral vegetative buds is much higher than that needed for terminal vegetative and flower buds. Trees that were exposed to daily alternating temperatures had lower levels of budbreak when the high temperature in the diurnal cycle was greater than 14 °C. Practically no budbreak was apparent on trees that were exposed to diurnal cycles with a high temperature of 20 °C for 8 hours. Budbreak on horizontally positioned trees was more than twice that on the vertically positioned trees, emphasizing the magnitude of the apical dominance effect and its strong masking of the chilling effect on lateral buds in vertically grown apple trees. Based on the data collected here we propose a new response curve for vegetative budbreak in `Golden Delicious·apple, within a temperature range between 0 to 15 °C.

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Particle film technology is a new tool for tree fruit production systems. Trials were performed in Santiago, Chile, and Washington and West Virginia to evaluate the effect of particle film treatments on apple [Malus sylvestris (L.) Mill var domestica (Borkh.) Mansf.] fruit temperature and the incidence of solar injury. Fruit surface temperature was reduced by the application of reflective particles and the amount of temperature reduction was proportional to the amount of particle residue on the fruit surface. Effective solar injury suppression was achieved with spray applications of 45 to 56 kg·ha-1 of a reflective, processed-kaolin particle film material in concentrations ranging from 3% to 12% in some of the locations. The timing of application to suppress solar injury was not clearly defined. The processed-kaolin particle film material was highly reflective to the ultraviolet wavelengths and this characteristic may be important in reducing solar injury to both fruit and leaves.

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