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Cameron P. Peace, Carlos H. Crisosto, Fredrick A. Bliss, and Thomas M. Gradziel

Candidate gene (CG) analysis can be an efficient approach for identifying genes controlling important traits in fruit production. Three chronological steps have been described for determining candidate genes for a trait—proposing, screening, and validating—and we have applied these to the problem of internal breakdown of peach and nectarine. Internal breakdown (IB), also known as chilling injury, is the collective term for various disorders that occur during prolonged cold storage and/or after subsequent ripening of stone fruit. Symptoms include mealiness, browning, and bleeding. Candidate genes for IB symptoms were proposed based on knowledge of the biochemical or physiological pathways leading to phenotypic expression of the traits. Gene sequences for proposed CGs were obtained primarily from the Genome Database for Rosaceae. Screening the CGs involved identifying polymorphism within a progeny population, relying mainly on simple PCR tests. Several polymorphic CGs were located on a peach linkage map and compared with phenotypic variation for IB susceptibility. A major QTL for mealiness coincided with the Freestone-Melting flesh locus, which itself is likely to be controlled by a CG encoding endopolygalacturonase, an enzyme involved in pectin degradation. Further gene sequences positioned on the consensus linkage map of Prunus by other researchers were co-located with QTLs for IB traits. Validation of the role of identified CGs will require detailed physiological or transgenic studies.

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Hendrik van Gorsel and Adel A. Kader

Internal breakdown (IB) is the limiting factor in the storage and postharvest handling of stone fruits. The symptoms of IB appear when fruits are kept for prolonged periods at temperatures below 10C and include leatheriness, mealiness, browning and bleeding of the flesh, and failure to ripen normally. We investigated the changes in phenolic compounds associated with IB of stone fruits. Twenty-eight phenolic compounds were separated by HPLC. Ten of these components were significantly affected by chilling temperatures. The concentration of six phenols changed in response to ripening after chilling temperatures, parallel to the appearance of IB symptoms. Most phenols showed a concentration gradient from the inside to the outside of the fruit, Comparison between peach cultivars showed characteristic differences in phenol metabolism during ripening. In both cultivars the most predominant phenol, chlorogenic acid, showed little change in concentration during storage. The structure of key phenolic compounds will be determined in order to elucidate the biochemical relationship between the phenols and the related enzymes. In this respect, a method was developed to detect phenylalanine ammonia-lyase (PAL) activity in peach fruit.

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Carlos H. Crisosto, R. Scott Johnson, Gayle M. Crisosto, John Labavich, and David Garner

During the past two seasons, the relationship between fruit ripening “ON” or “OFF” the tree and internal breakdown incidence was studied with `Elegant Lady' and `O'Henry' peach cultivars. Internal breakdown (IB) visual symptom development was delayed in fruit harvested at different physiological maturities and exposed to different “OFF” the tree pre-ripening treatments. As a follow up, different pre-ripening treatments (controlled delayed cooling) were tested for several peach, nectarine, and plum cultivars susceptible to IB. This pre-ripening treatment delayed flesh browning, mealiness, and off-fl avor development after a simulated shipment and retailer handling period for `Flavorcrest', `Elegant Lady', `O'Henry', `Parade', `Fairtime', `Carnival', `Prima Gattie', `Last Chance', `Autumn Gem', `Autumn Lady', and `Autumn Rose' peaches; `Summer Grand' and `September Red' nectarines; and `Fortune' plum. However, decay development may be a problem. Delayed cooling at 20°C must be carried out with fruit protected with fungicide and wax for the shortest possible, but still effective, length of time to limit IB. The temperature and the length of this pre-ripening treatment, and the presence or absence of ethylene during the delayed cooling is cultivar dependent. Thus, specific pre-ripening conditions must be developed for each cultivar.

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George D. Nanos and F. Gordon Mitchell

Storage at 0C of `O'Henry' and `Fairtime' peaches and `Red Jim' and `September Grand' nectarines (Prunus persica L. Batsch) resulted in significantly longer postharvest life than did storage at 5C, due to differences in the development of internal breakdown (IB) symptoms. Conditioning at 20C for 2 days before storage at 0 or 5C generally prolonged the storage life of fruit of these cultivars. The use of elevated CO2 during conditioning helped maintain fruit firmness. Addition of 5% CO2 to air gave the best results in maintaining fruit firmness and freedom from IB symptoms for up to 6 weeks. Reducing the O2 content kept flesh firmness high after storage but did not delay the appearance of IB. Conditioning at 30C using various atmospheres was less effective than conditioning at 20C.

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Maude Lachapelle, Gaétan Bourgeois, Jennifer R. DeEll, Katrine A. Stewart, and Philippe Séguin

evaluated only for incidence of soggy breakdown. Internal ethylene concentration was evaluated by extracting a 3-mL gas sample from the core of each apple using a syringe and then injecting the sample into a Varian CP-3380 Gas Chromatograph (Varian Canada

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Jinwook Lee, James P. Mattheis, and David R. Rudell

evaluate the incidence and severity of internal flesh breakdown ( Fig. 1 ). Disorder incidence is expressed as percent fruit affected (n = 18). For fruit with disorders, symptom severity was scored as 1 = 1% to 10%, 2 = 11% to 25%, 3 = 26% to 50%, 4 = 51

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Jinwook Lee, James P. Mattheis, and David R. Rudell

). ‘Royal Gala’ apples are also susceptible to the development of flesh breakdown during and after cold storage ( Lee et al., 2013 ). However, flesh breakdown development can be delayed following fruit exposure to 1-MCP ( Lee et al., 2013 ). Nonetheless, 1

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Christopher B. Watkins and Jacqueline F. Nock

susceptibility of fruit is common for many disorders, e.g., bitter pit ( Ferguson and Watkins, 1989 ), senescent breakdown ( Marmo et al., 1985 ), and external and internal CO 2 injury ( Watkins et al., 1997 ; Watkins and Liu, 2010 ). Although at least one

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Jinwook Lee, James P. Mattheis, and David R. Rudell

then fruit were horizontally sliced into five or six sections. Incidence and severity of flesh breakdown were assessed. Disorder incidence was expressed as percent fruit affected ( n = 18). The severity of external and internal physiological disorders

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Max G. Villalobos-Acuña, William V. Biasi, Sylvia Flores, Elizabeth J. Mitcham, Rachel B. Elkins, and Neil H. Willits

be stored for 2 to 3 months in air under ideal conditions at –1 to 0 °C. The postharvest life of ‘Bartlett’ pears generally is limited by the appearance of scald (storage or senescent scald) and internal breakdown, physiological disorders