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the light conditions after chilling ( Lasley et al., 1979 ; Rietze and Wiebe, 1989 ). Watermelon is susceptible to CI but is more resistant than cucumber ( Wehner and Mirdad, 1994 ). Low-temperature effects have been studied on germination, seedling

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December is 62 °F (16.7 °C) and of January is 59 °F (15 °C)]. The peach selections are adapted in areas where ‘EarliGrande’ ( Bowen, 1980 ) and ‘TropicBeauty’ can be grown commercially. These low-chill regions normally receive less than 200 chilling units

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The production of temperate zone fruit crops in subtropical environments has increased significantly in the last 30 years. Low-chill cultivars of apple, blueberries, plum, and peach have been developed by several breeding programs and are in

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°24′36″W). The chilling hours (hours below 7.2 °C) accumulated at the three sites during the winter of 2004 to 2005 were 402 (north-central Florida), 162 (central Florida) and 125 (southwest Florida). Four low-chill peach cultivars [Flordaglo (150 cu

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failure, blind nodes appear to be incited by high temperatures during bud development ( Boonprakob and Byrne, 1990 ). The objective of this study was to evaluate the performance of four low-chill peach cultivars at three locations in Florida with respect

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A computer program was developed to calculate the percent contribution of the founding parents for any given peach or nectarine (Prunus persica) cultivar. The founding parents used most frequently for three low-chill (0 to 500 chill units) peach and nectarine breeding programs (Florida and Pelotas and Campinas, Brazil) were determined. The Florida program used several low-chill honey type peaches (`Hawaiian', `Okinawa') as a source of low chilling and then did extensive crossing with higher quality cultivars developed mainly in the northeastern United States. About 50% of the background of the Brazilian peach releases consists of local selections that were originally brought by the Portuguese explorers. Although each of the Brazilian programs used local peach materials, the local peaches used by each program are different. In addition, the program at Pelotas used germplasm from the Georgia–Florida and New Jersey breeding programs and the Campinas program used `Jewel' (honey peach) and several Florida nectarines (`Sunlite', `Sunred') in their development work. The founding parents among these three programs, although there is some common parentage, are different, and the intercrossing of materials from the various programs would be a useful approach to create more diversity in this germplasm.

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Low chill `Flordaprince' peach trees were grown in subtropical Australia, either following paclobutrazol application to dwarf the trees, or extra nitrogen to invigorate them. Fruits were thinned uniformly. Paclobutrazol significantly reduced the competing spring shoot growth and gave earlier maturity of larger, better quality fruits. It reduced the spring, but increased the autumn root flush. Stage 2 of fruit growth was slightly longer in vigorous trees, resulting in delayed seed growth and greater dry mass of the embryos. Starch reserves were greatest in the roots, followed by the trunk, shoots and leaves. The reserves were lowest during the second half of fruit development, but rose again after the end of shoot extension growth. Leaf N, P, and K levels decreased through the season while Ca and Mg increased. There were significantly lower K and higher Ca and Mg levels in dwarfed trees.

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Abstract

Breeding low-chilling peach and nectarine cultivars began in Florida in 1953. Objectives were to produce low-chilling, early-ripening peach cultivars with fruit qualities equal to temperate-zone cultivars. Low chilling was essential for local adaptation (4). Early ripening was essential to allow production of the earliest-season peaches on the domestic market with little competition from other states and to allow harvest of the crop during the relatively dry period of late April and May. Feral selections descended from Spanish seed introductions through St. Augustine, Fla., seed importations from Okinawa, and ‘Hawaiian’, a South China clone, served as the main sources of low chilling (18). These sources were hybridized with high-chilling U.S. clones having commercial fruit qualities. Resultant seedlings were selected for best adaptation and improvement in fruit qualities above that of the low-chilling parents. Chilling requirements of progeny were near midparent values; chilling requirements of the F2 seedlings ranged from equal to the low parent to equal to the high parent (14), indicating that many genes are involved in chilling. Selections were intermated, and low-chilling progeny were hybridized with other high-chilling U.S. clones, resulting in more progenies for further selection. Commercial fruit size and satisfactory horticultural qualities were obtained after six generations of crosses and backcrosses. Clonal selections made during these six generations and in subsequent generations serve as the basis for most low-chilling cultivars currently grown in Florida, southern Texas, and southern California. Selections from this program are either grown commercially or being evaluated in many tropical and tropical highland areas of the world (11, 16, 19, 24).

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Almond production is restricted to areas with at least 300 chill units. Selection of plants with lower chilling requirements is a priority in our area. The progenies of two low chilling cvs. `Rané' and `Constantini' and one of medium chilling cv. `Cavaliera' were chosen for this study. The selected trees were open pollinated and 100 seeds of each variety were planted on individual pots after three week stratification. Three groups were formed according to the speed of germination and transplanted to the nursery. The date of blooming of each individual was recorded. A positive correlation was found between time of blooming of the progenitor and that of the progeny regardless of the origin. On the descendence of `Cavaliera', a positive correlation between speed of germination and bloom date was observed. However on `Constantini' and `Rané' progenies, the same correlation had no significance. `Cavaliera' produced a 45% of low chilling requirement descendants, `Rané' had 67% and `Constantini' had the higher ability to transmit the low chilling character with a 78% of the progeny with that trait.

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The severity of chilling injury in zucchini squash stored at 5C than transferred to 20C was reduced with the prestorage treatment of 42C hot water for 30 min. The chilling injury was further reduced when squash were preconditioned at 15C for 2 days after hot water treatment but before the 5C storage. Squash stored at 15C did not develop any symptoms of chilling injury. However, weight loss was most severe in squash stored at 15C. Squash kept at 5C had the least weight loss during the 2-week storage. Weight losses were comparable in squash treated or not treated with hot water. Analysis of polyamines in squash preconditioned with high and low temperatures is in progress. The effect of hot water treatment on the changes of putrescine, spermidine, and spermine and its implication in reducing chilling injury will be discussed.

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