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María José Arismendi, Patricio Hinrichsen, Ruben Almada, Paula Pimentel, Manuel Pinto and Boris Sagredo

, 2006 ). Stone fruit production occupies ≈43,000 ha ( Instituto Nacional de Estadística, 2007 ) distributed in different regions of the country, which provides adequate climatic conditions with cold-hours and degree-days that allow early and late

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David H. Byrne

Despite the hundreds of existing stone fruit (Prunus spp.) cultivars used for fresh market, there is a continuing need to develop new stone fruit cultivars as the requirements of the industry change. Over the last 20 years there has been a shift toward private breeding as the public sector decreases its support of these long-range programs. As a result there are fewer public breeding programs and many of those still operating protect their releases and partially fund their programs with royalty payments. Other trends that are shaping the development of new stone fruit cultivars are a need for smaller or more easily managed tree architecture, a trend toward the use of fewer agricultural chemicals, the expansion of production zones into the milder winter zones to allow year-round availability of stone fruit, a general diversification of fruit types being marketed, the increased awareness of the health benefits of fruit consumption, the need for better and more consistent quality, and given the global marketing of these fruit the increased need for enhanced postharvest qualities. The breeding programs of the world are responding to these trends and working toward developing the cultivars for the world markets of the future.

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Carlos H. Crisosto, David Slaughter, R. Scott Johnson, Luis Cid and David Garner

Maximum maturity indices for different packinghouse conditions based on cultivar critical bruising thresholds and bruising potentials were developed for stone fruit cultivars. The critical bruising thresholds, based on fruit firmness, and the bruising probabilities varied among stone fruit cultivars. In general, plums tolerated more physical abuse than yellow-fl esh peach, nectarine, and white-flesh peach cultivars. Impact location on the fruit was an important factor in the determination of critical bruising thresholds. Potential sources of bruising damage during fruit packing were located using an accelerometer (IS-100). A survey of different packinghouses revealed that bruising potentials varied from 21 to 206 G. Bruising potential was reduced by adding padding material to the packinglines, minimizing height differences at transfer points, synchronizing timing between components, and reducing the operating speed. Bruising probabilities for the most-susceptible California-grown cultivars at different velocities and Gs have been developed. Development of a practical sampling protocol to determine fruit firmness during maturation was studied.

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Stephen Southwick*

Quality of stone fruit is defined by fruit size, color, firmness, flavor, shape, general appearance, adhesion and size of the stone and fruit surface characteristics (e.g. fuzz, abrasions, pest damage). Cultural practices, such as pruning, nutrition, irrigation, growth regulator usage and pesticide applications can influence these quality characteristics to a greater or lesser extent. Adequate potassium nutrition can improve soluble solids and fruit size in plums. Excess nitrogen fertilization can soften peaches. Well-timed calcium sprays are thought to improve the firmness of sweet cherries, as are applications of gibberellin. Ethylene synthesis inhibitor usage can alter the timing of ripening, reduce early fruit drop and improve storage. Irrigation scheduling is a tool that can be used to regulate final fruit size and firmness, as well as time of maturation. Selective pruning is used to structure a tree's architecture for improved light penetration to improve fruit size and color. These and other production practices will be discussed in relation to how they affect fruit quality in stone fruit.

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A. Erez, Z. Yablowitz and R. Korcinski

Fresh fruits of stone fruit species are either lacking or in short supply in the months of March and April on the world market. This results from the absence of late-maturing cultivars in most of these species and from their poor storage capabilities. In March–April, supply from the Southern Hemisphere is dwindling or finished, while supply from the Northern Hemisphere has not started yet. A horticultural system was developed in Israel to get early fruit ripening of stonefruit species. The system developed is based on early completion of dormancy requirements followed by greenhouse tree growing. The system uses the following elements: 1) Improve chilling accumulation in winter by using evaporative cooling, to prevent chilling negation by high day temperatures. 2) Monitor salt accumulation level to prevent damage to branches and buds. 3) Monitor bud temperature and evaluate dormancy development according to the dynamic model. 4) Use dormancy breaking chemicals to compensate for part of the chilling not applied. 5) Cover of the trees with polyethylene having the appropriate characteristics of light filtering. 6) Keep the temperature in the greenhouse lower than the maximal temperature allowed, at every specific stage of development by ventilation. By using this system, fruit ripening was advanced by 4 to 6 weeks in peaches and nectarines (harvested from late March) and by 4 weeks in sweet cherries (harvested from April 11). Yields of 20 to 30 tons/ha were obtained in both species with high fruit quality.

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Esmaeil Fallahi, Michael Colt, S. Krishna Mohan and John Fellman

Influence of prebloom and full bloom applications of hydrogen cyanamide on `Simka' and `Friar' plums in Southwest Idaho and `Florda Prince' peach in Southwest Arizona was studied. Prebloom application of 0.5% hydrogen cyanamide caused severe toxicity to the fruit buds in `Friar' lure, while 2% hydrogen cyanamide did not cause toxicity in `Simka' plum. `Simka' fruit was effectively thinned with 1-2% prebloom application. At full bloom, 1.5% hydrogen cyanamide caused severe flower and leaf burning in both `Friar' and `Simka' plums, while concentrations between 0.1% and 1% thinned flowers (fruits) in both of the plum cultivars. Influence of hydrogen cyanamide on final fruit set, fruit size and maturity are also studied. Prebloom or full bloom applications of 2% or 3% hydrogen cyanamide eliminated 95 to 100% of the blooms, while application of this chemical at 1% sufficiently thinned the fruit. Number of commercially packed large peaches in trees receiving 1% hydrogen cyanamide was the same as that in trees thinned by hand, suggesting hydrogen cyanamide as a potential chemical for stone fruit thinning.

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Michael J. Willett, Preston K. Andrews and Edward L. Proebsting Jr.

There has been an explosion of interest in the development of computer-based Decision Support Systems (DSS) in agriculture. Humans factor, which is the design and evaluation of a system to optimize human and total system performance, offer tools to improve the usefulness of DSS. Task analysis, a formal human factors approach to study human-machine interaction, identifies all of the physical and psychological tasks which must be completed by either the human or the machine in order to meet the various system performance requirements and constraints. Our study focuses on the tasks associated with mid-winter stone fruit freeze protection. Using this technique we have identified work load and output requirements of current critical temperature estimation procedures, additional information needed to improve critical temperature estimates and training needs of fruit industry personnel making critical temperature determinations. This information will be used to produce a requirements specification for a freeze protection DSS.

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Stephen M. Southwick and Kitren Glozer

Many commercially grown stone fruit including apricots (Prunus armeniaca L.), peaches and nectarines [P. persica (L.) Batsch], plums (P. salicina Lindl., P. domestica L.), prunes (P. domestica L.), and pluots (P. salicina × P. armeniaca) have a tendency to produce high numbers of flowers. These flowers often set and produce more fruit than trees can adequately size to meet market standards. When excessive fruit set occurs, removal of fruit by hand thinning is necessary in most Prunus L. species to ensure that remaining fruit attain marketable size and reduce biennial bearing. Over the years there have been numerous attempts to find chemical or physical techniques that would help to reduce the costs associated with and improve efficiencies of hand thinning, however, alternate strategies to hand thinning have not been widely adopted for stone fruit production. In the past 10 years, several chemical treatments have shown promise for reducing hand thinning needs in stone fruit. Management of flowering by chemically reducing the number of flowers has been particularly promising on stone fruit in the Sacramento and San Joaquin Valleys of California. Gibberellins (GAs) applied during May through July, have reduced flowering in the following season in many stone fruit cultivars without affecting percentage of flowers producing fruit. As a result, fruit numbers are reduced, the need for hand thinning is reduced and in some cases eliminated, and better quality fruit are produced. There are risks associated with reducing flower number before climatic conditions during bloom or final fruit set are known. However, given the changes in labor costs and market demands, the benefits may outweigh the risks. This paper reviews relevant literature on thinning of stone fruit by gibberellins, and summarizes research reports of fruit thinning with GAs conducted between 1987 and the present in California. The term thin or chemically thin with regard to the action of GA on floral buds is used in this paper, consistent with the literature, although the authors recognize that the action of GA is primarily to inhibit the initiation of floral apices, rather than reduce the number of preformed flowers. At relatively high concentrations, GA may also kill floral buds. Chemical names used: gibberellic acid, potassium gibberellate.

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Stephen M. Southwick

Commercially grown apricots (Prunus armeniaca), peaches (Prunus persica), nectarines (Prunus persica), plums (Prunus salicina and Prunus domestica), and pluots (Prunus salicina × Prunus armeniaca) have a tendency to produce high numbers of flowers. These flowers often set and produce more fruit than trees can adequately size to meet market standards. When excessive fruit set occurs, removal of fruit by hand-thinning is common to ensure that fruit size meets market standards. Over the years there have been numerous attempts to find chemical or physical techniques that would help to reduce costs associated with and improve efficiencies of hand-thinning; however, using alternate strategies to hand-thinning have not been widely adopted in stone fruit production. In the past 10 years, through the continuing efforts of scientists throughout the world in public and private institutions and business, it appears that there are chemical sprays capable of reducing the need for hand-thinning in stone fruit. Management of flowering by reducing the number of flowers on apricot, peach, nectarine, plum, and prune has shown promise under climatic conditions such as those found in the San Joaquin Valley of California. By applying gibberellins during May through July, flowers in many stone fruit cultivars can be reduced in the following season. The reduction in flower number does not generally lead to an increase in fruit set. As a result, fruit numbers are reduced, the need for hand thinning can be reduced, and in some cases eliminated. There are risks associated with reducing flower number before climatic conditions during bloom or final fruit set are known. However, given the changes in labor costs and market demands, especially in the developed world, the benefits may outweigh the risks. The application and implications of these summer gibberellin applications toward reducing flower numbers will be discussed as it relates to commercial stone fruit growing.

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Shengrui Yao

's Day and an even more severe one in early February. Crops across the state suffered various kinds of winter damage depending on their hardiness and location. For fruit crops, stone fruit suffered more damage than pome fruit. The last disastrous freeze