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James J. Luby, Peter A. Alspach, Vincent G.M. Bus, and Nnadozie C. Oraguzie

Incidence and severity of fire blight [Erwinia amylovora (Burr.) Winslow, Broadhurst, Buchanan, Krumwiede, Rogers, and Smith] following field infection were recorded using families resulting primarily from open-pollination of Malus sylvestris (L.) Mill. var.domestica (Borkh.) Mansf. cultivars and a few other Malus Mill. sp. The families were structured as three sublines, planted in three successive years (1992 to 1994), of a diverse population of apple germplasm established at HortResearch, Hawkes Bay, New Zealand. The incidence of fire blight varied among the sublines with the oldest planting exhibiting more fire blight. Flowering trees were more likely to be infected than nonflowering trees, in terms of both incidence and severity. Furthermore, the level of fire blight was related to flowering date, with later flowering trees having higher levels. Thus, family means and narrow-sense heritability estimates were computed after first adjusting the fire blight score for flowering date by fitting a linear model. Provenance of origin of the maternal parent explained little variation except that M. sieversii Lebed. families were more resistant than M. sylvestris var. domestica families in one subline. Family means computed using all trees, and those from only flowering trees were highly correlated. Families from open-pollination of M. honanensis Rehder and M. xhartwiggii Koehne females were among the more susceptible. Those from several European M. sylvestris var. domestica cultivars as well as from M. baccata (L.) Borkh. and M. toringoides (Rehder) Hughes females were among the more resistant families. Narrow-sense heritability estimates ranged from 0.05 to 0.85 depending on the subline, with most estimates between 0.12 and 0.36. They were higher in the two older sublines that consisted primarily of open-pollinated families from M. sylvestris var. domestica, and lower in the younger subline that consisted primarily of M. sieversii, due to lower incidence and severity in the latter subline. Breeders who consider potential complications of juvenility, tree size, and flowering date in relation to infection periods should be able to exploit field epidemics to perform effective selection.

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I. Lara and M. Vendrell

ABA and ethylene treatments were applied to preclimacteric `Granny Smith' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] harvested at three different maturity stages. Ethylene production rates, ethylene-forming capacity (EFC), free and conjugated ACC contents, presence of ACC oxidase (ACO) and ripening-related ACC synthase (ACS) proteins, and endogenous ABA levels were monitored at harvest and during 3 weeks thereafter. ABA treatment resulted in a specific accumulation of ACO protein and of ACS-related polypeptides in fruit collected ≈2 months before commercial harvest, whereas the same tissues showed no response to exogenous ethylene. In contrast, fruit harvested 1 month later proved more sensitive to ethylene but not to ABA, in accordance with evolution of endogenous ABA levels, which were highest at this maturity stage and were enhanced in response to exogenous ethylene. A possible role for ABA as an inductor of the competency to ripen is discussed. Chemical names used: abscisic acid (ABA); 1-aminocyclopropane-1-carboxylic acid (ACC).

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Nobuhiro Kotoda, Masato Wada, Sadao Komori, Shin-ichiro Kidou, Kazuyuki Abe, Tetsuo Masuda, and Junichi Soejima

Two apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] homologous fragments of FLO/LFY and SQUA/AP1 (AFL and MdAP1, respectively) were analyzed to determine the relationship between floral bud formation and floral gene expression in `Jonathan' apple. The AFL gene was expressed in reproductive and vegetative organs. By contrast, the MdAP1 gene, identified as MdMADS5, which is classified into the AP1 group, was expressed specifically in sepals concurrent with sepal formation. Based on these results, AFL may be involved in floral induction to a greater degree than MdAP1 since AFL transcription increased ≈2 months earlier than MdAP1. Characterization of AFL and MdAP1 should advance the understanding of the processes of floral initiation and flower development in woody plants, especially in fruit trees like apple.

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D. Michael Glenn, Amnon Erez, Gary J. Puterka, and Patricia Gundrum

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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D. Michael Glenn, Gary J. Puterka, Stephen R. Drake, Thomas R. Unruh, Allen L. Knight, Pedro Baherle, Ernesto Prado, and Tara A. Baugher

Particle film technology is a developing pest control system for tree fruit production systems. Trials were performed in Santiago, Chile, and York Springs, Pa., Wenatchee and Yakima, Wash., and Kearneysville, W. Va., to evaluate the effect of particle treatments on apple [Malus sylvestris (L.) Mill. var. domestica (Borkh) Manst.] leaf physiology, fruit yield, and fruit quality. Leaf carbon assimilation was increased and canopy temperatures were reduced by particle treatments in seven of the eight trials. Yield and/or fruit weight was increased by the particle treatments in seven of the eight trials. In Santiago and Kearneysville, a* values of the fruit surface were more positive in all trials although a* values were not increased in Wenatchee and Yakima. Results indicate that particle film technology is an effective tool in reducing heat stress in apple trees that may result in increased yield potential and quality.

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D.R. Rudell, J.P. Mattheis, X. Fan, and J.K. Fellman

Effects of artificial ultraviolet-visible light and methyl jasmonate (MJ) treatment on `Fuji' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit peel anthocyanin, phenolic, carotenoid, and chlorophyll production were examined using tristimulus color analysis and reverse-phase high performance liquid chromatography. Anthocyanin synthesis was enhanced by light and MJ treatment. Chlorogenic acid and most cyanidin, quercetin, and phloretin glycosides increased with MJ treatment concentration. Light alone also promoted increased production of most of these compounds. Production of catechin, (-)epicatechin, quercetin, and quercetrin was not enhanced by either light or MJ treatment. Light and MJ enhanced ß-carotene and chlorophyll b, synthesis but not xanthophyll or chlorophyll a synthesis. The chlorophyll a/b ratio decreased with MJ dosage. Results suggest MJ may provide a viable means of enhancing apple fruit coloration and other photoprotective mechanisms. Chemical name used: methyl 3-oxo-2-(2-pentenyl)cyclopentane-1-acetate (methyl jasmonate).

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D. Michael Glenn, Ernesto Prado, Amnon Erez, James McFerson, and Gary J. Puterka

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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Xuetong Fan, Sylvia M. Blankenship, and James P. Mattheis

An ethylene action inhibitor, MCP, was applied to preclimacteric and climacteric apple [Malus sylvestris L. (Mill.) var. domestica Borkh. Mansf.] fruit. Experiments were conducted in North Carolina and Washington State utilizing the following cultivars: Fuji, Gala, Ginger Gold, Jonagold, and Delicious. MCP inhibited loss of fruit firmness and titratable acidity when fruit were held in storage at 0 °C up to 6 months and when fruit were held at 20 to 24 °C for up to 60 days. For all cultivars except `Fuji', differences in firmness between treated and nontreated fruit exceeded 10 N after 6 months storage. These beneficial effects were seen in both preclimacteric and climacteric fruit. Ethylene production and respiration were reduced substantially by MCP treatment. MCP-treated fruit had soluble solids equal to or greater than those in nontreated fruit. Storage and shelf life were extended for all cultivars tested. Chemical name used: 1-methylcyclopropene (MCP).

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James D. Hansen

Durations of ultrasound treatments were evaluated for efficacy in removing or destroying external pests of apples (Malus sylvestris var domestica). Egg hatch of codling moth (Cydia pomonella; Lepidoptera: Tortricidae), was inversely related to time of ultrasound exposure, although egg mortality was less than 60% after 45 min of treatment. Mortality of twospotted spider mite (Tetranychus urticae; Acari: Tetranychidae), and western flower thrips (Frankliniella occidentalis; Thysanoptera: Thripidae), was directly related to ultrasound durations; adding detergent to the ultrasound bath increased treatment efficacy. Ultrasound did not remove san jose scale (Quadraspidiotus perniciosus; Homoptera: Diaspididae), from the fruit surface. Ultrasound, which can be incorporated in the packing line, shows promise as a postharvest phytosanitation treatment against external pests.

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Paul T. Dauny and Daryl C. Joyce

Better maintenance of firmness and suppression of ethylene production in 'Queen Cox' and 'Bramley' apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit was achieved by prestorage applications of 1-MCP. 1-MCP concentration, exposure time and exposure temperature ranges of 0.1 to 10.0 μL·L-1 1-MCP, 6 to 48 h, and 0 to 20 °C, respectively, were effective on fruit subsequently stored for 2 ('Cox') and 3 ('Bramley') months in air at 3 to 4 °C. However, 1-MCP had little effect on either firmness or ethylene production after 4 ('Cox') or 6 ('Bramley') months storage. Nonetheless, 1-MCP treated 'Bramley' fruit had reduced rot and superficial scald incidences compared with untreated control fruit. Chemical name used: 1-methylcyclopropene (1-MCP).