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Zhiguo Ju and William J. Bramlage

Influences of fruit maturity, AVG and ethephon preharvest treatments, and storage conditions on cuticular phenolic concentration, α-farnesene accumulation and oxidation, and scald development of `Delicious' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] were studied. Advanced maturity and ethephon treatment increased free phenolics in fruit cuticle at harvest, while AVG treatment caused a reduction. Free cuticular phenolics increased during early storage in ethephon-treated and nontreated fruit but not in AVG-treated apples. Advanced maturity and ethephon did not alter α-farnesene accumulation overall, but reduced conjugated triene (CT281) formation and scald development. When stored in a low-ethylene room (<1 μL·L-1), AVG-treated fruit accumulated very low levels of α-farnesene and CT281 and did not develop scald after 6 months at 0 °C. When stored in a commercial room (ambient ethylene >5 μL·L-1), the AVG-treated and control fruit accumulated similar amounts of α-farnesene and CT281 and developed similar percentages of scald. In general, free phenolic concentrations in fruit cuticle were negatively correlated with CT281 formation and scald development of apples. Chemical names used: aminoethoxyvinylglycine (AVG); 2-chloroethylphosphonic acid (ethephon).

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David R. Rudell and James P. Mattheis

`Golden Delicious' apple [Malus sylvestris var. domestica (Borkh.)] cortex disks suspended in solutions containing a nitric oxide (•NO) donor [S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP)], •NO gas, or nitrite (KNO2) were used to identify impacts of •NO on ethylene production and NO2 on •NO and ethylene production. Treatment with GSNO or SNP reduced ethylene biosynthesis compared with control treatments containing equimolar concentrations of oxidized glutathione (GSSG) or Na4(CN)6 respectively. Apple disk exposure to •NO gas did not impact ethylene production. Treatment with NO2 resulted in increased •NO production and decreased ethylene biosynthesis. Generation of •NO increased linearly whereas ethylene generation decreased exponentially with increasing NO2 treatment concentration. •NO was enhanced in autoclaved tissue disks treated with NO2 , suggesting that its production is produced at least in part by nonenzymatic means. Although this evidence shows •NO is readily generated in apple fruit disks by NO2 treatment, and ethylene synthesis is reduced by •NO/NO2 generated in solution, the exact nature of •NO generation from NO2 and ethylene synthesis modulation in apple fruit disks remains to be elucidated.

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Rongcai Yuan and Duane W. Greene

BA was applied at 50 or 100 mg·L-1 to `More-Spur McIntosh'/Malling 7 (M.7) apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] at the 10 mm stage of fruit development. BA thinned fruit and increased fruit size. There were two distinguishable peaks of fruit abscission during `June drop'. BA accentuated the naturally occurring waves of fruit abscission, and enhanced translocation of 14C-sorbitol from leaves to fruit when applied directly to the fruit, but not when applied directly to the leaves. Net photosynthesis was decreased and dark respiration was increased when temperature following BA application was high (30 °C), whereas there was no effect when temperature was lower (20 °C). Total nonstructural carbohydrates, total soluble sugars, and starch in the leaves decreased dramatically over the 12- or 13-day observation period, regardless of BA treatment. These carbohydrate concentrations in the leaves were lowered further by BA application. Abscising fruit, based on specific reddening of the pedicel, had higher carbohydrate levels than persisting fruit, regardless of BA application. We conclude that BA thins fruit, at least in part, by increasing dark respiration and decreasing net photosynthesis. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)].

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C.B. Watkins and F.W. Liu

-Methylcyclopropene (1-MCP) increases CO 2 injury in apples Acta Hort. 600 277 280 Derkacz, M. Elfving, D.C. Forshey, C.G. 1993 The history of the ‘Empire’ apple Fruit Var. J. 47 70 71 Fawbush, F. Nock, J.F. Watkins, C.B. 2008 External carbon dioxide injury and 1

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I.J. Warrington, T.A. Fulton, E.A. Halligan, and H.N. de Silva

Container-grown `Delicious', `Golden Delicious', `Braeburn', `Fuji' and `Royal Gala' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees, on Malling 9 (M.9) rootstock, were subjected to a range of different maximum/minimum air temperature regimes for up to 80 days after full bloom (DAFB) in controlled environments to investigate the effects of temperature on fruit expansion, final fruit weight, and fruit maturation. Fruit expansion rates were highly responsive to temperature with those at a mean of 20 °C being ≈10 times greater than those at a mean of 6 °C. All cultivars exhibited the same general response although `Braeburn' consistently showed higher expansion rates at all temperatures compared with lowest rates for `Golden Delicious' and intermediate rates for both `Delicious' and `Fuji'. The duration of cell division, assessed indirectly by measuring expansion rate, appeared to be inversely related to mean temperature (i.e., prolonged under cooler conditions). Subsequently, fruit on trees from the coolest controlled temperature treatment showed greater expansion rates when transferred to the field and smaller differences in fruit size at harvest than would have been expected from the measured expansion rates under the cool treatment. Nonetheless, mean fruit weight from warm postbloom treatments was up to four times greater at harvest maturity than that from cool temperature treatments. Postbloom temperature also markedly affected fruit maturation. Fruit from warm postbloom temperature conditions had a higher soluble solids concentration, more yellow background color, lower flesh firmness, and greater starch hydrolysis than fruit from cooler temperatures.

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Richard P. Marini

For 4 years, `Redchief Delicious' apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees were treated with ethephon and/or Accel (6-BA + Gibberellins 4+7) when average fruit diameter was 5.0 to 11.4 mm. Effective thinning was obtained with ethephon at concentrations >500 mg·L-1 and with Accel at concentrations of 100 to 125 mg·L-1. In only 1 year out of 4 did combinations of Accel plus ethephon reduce fruit set more than either material applied alone. Repeat applications of either material alone or in combination reduced fruit set no more than single applications. Fruit weight was negatively related to the number of fruit per tree. After adjusting fruit weight for number of fruit per tree at harvest with analysis of covariance, ethephon did not improve fruit weight at harvest, but Accel improved fruit weight in two of three experiments. The effect of combinations of Accel and ethephon on fruit weight was inconsistent. Chemical names used: 2-chloroethyl phosphonic acid (ethephon); polyothyethylleneploypropanol dihydroxy-propane 2, butoxyethanol (Regulaid); N-(phenylmethyl)-1H-purine-6-amine plus giberrellins A4 + A7 (Accel).

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Desmond R. Layne, Zhengwang Jiang, and James W. Rushing

Replicated trials were conducted in Summers 1998 and 1999 at two commercial orchards (A and B) to determine the influence of a metalized, high density polyethylene reflective film (SonocoRF) and aminoethoxyvinylglycine (ReTain), on fruit red skin coloration and maturity of `Gala' apples (Malus sylvestris var. domestica). There were four experimental treatments: 1) nontreated control; 2) reflective film (RF); 3) ReTain; and 4) RF + ReTain. RF was applied 4 weeks before anticipated start of harvest by laying a 5-ft-wide (150-cm) strip on each side of the tree row in the row middle. ReTain was applied 4 weeks before harvest at the commercial rate in one orchard and at 60% of the commercial rate in a second test. ReTain delayed fruit maturity. Fruit from RF trees had a significantly greater percent surface red color than fruit from trees not treated with RF. Fruit from RF + ReTain were significantly redder and had higher soluble solids concentration (SSC) than fruit from trees treated with ReTain alone. There were no differences in size, fruit firmness or starch content between fruit from RF and RF + Retain. RF appears to be a method to increase red skin coloration in `Gala' apples treated with ReTain without adversely impacting maturity.

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Iwan F. Labuschagné, J.H. Louw, Karin Schmidt, and Annalene Sadie

Genetic variation in chilling requirement was investigated over three growth periods using clonal progenies of six apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] families derived from crosses of high and low chill requiring cultivars. Two quantitative measurements related to chilling requirement, viz., the time of initial budbreak (vegetative and reproductive) and the number of breaking buds over a specified time interval, were used as evaluation criteria. Genetic and environmental variances of the traits are presented as intra-class correlation coefficients for clones within and between families. For budbreak time, reproductive and vegetative, broad-sense heritability averaged around 75% and 69% respectively, indicating a high degree of genetic determination in this material. For budbreak number, moderate to low genetic determination was found with broad-sense heritabilities around 30%. Estimates of genetic components of variance between families were generally very low in comparison to the variance within families and predict potentially favorable responses to truncation selection on the traits within these progeny groups. Analysis of the data showed that distribution of budbreak time is typical of quantitative traits with means distributed closely around midparent values. Skewed distributions towards low budbreak number were obtained in varying degrees in all families.

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Hiroshi Iwanami, Shigeki Moriya, Nobuhiro Kotoda, Sae Takahashi, and Kazuyuki Abe

Changes in flesh firmness and mealiness during storage were investigated in 24 apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivars and selections (genotypes) up to 40 days after harvest under 20 ± 2 °C and 85% ± 5% relative humidity storage conditions. Flesh firmness was measured using a penetrometer, while mealiness was quantified by measuring the degree of cell separation in tissue induced by shaking discs of tissue in a sucrose solution. According to the relationship between the change in firmness and mealiness, the genotypes can be divided into four groups: those that did not soften and remained hard and nonmealy during storage; those that softened without mealiness; those that softened with slight mealiness; and those that softened with mealiness. Firmness decreased below 30 N in fruit that softened with mealiness, and the minimum firmness during storage was correlated with the degree of mealiness at 30 days of storage. The rate of softening was the highest in fruit that softened with mealiness. Therefore, it was concluded that, by measuring the firmness and changes in firmness that take place during storage, the genotypes resulting in softening with mealiness and those that result in softening without mealiness could be identified.

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Wesley Autio*, John Cline, Robert Crassweller, Charles Embree, Elena Garcia, Emily Hoover, Kevin Kosola, Ronald Perry, and Terence Robinson

`McIntosh' apple trees [Malus ×sylvestris (L.) Mill. Var domestica (Borkh.)] on five semidwarfing rootstocks (CG.4814, CG.7707, G.30N, M.7 EMLA, and Supporter 4) were planted at 10 locations (MA, MI MN NS 2 in NY ON PA VT and WI) under the direction of the NC-140 Multistate Research Project. After four growing seasons (through 2002), trees on CG.7707, G.30N, Supporter 4, and M.7 EMLA were significantly larger than those on CG.4814. Cumulative root suckering was most from trees on M.7 EMLA, and least from trees on CG.7707, G.30N, and Supporter 4. Yield per tree in 2002 and cumulatively was greatest from trees on G.30N and least from trees on CG.7707 and M.7 EMLA. In 2002 and cumulatively, CG.4814 resulted in the greatest yield efficiency, and M.7 EMLA resulted in the lowest. In 2002, fruit from trees on M.7 EMLA were largest, and those from trees on CG.4814 were smallest. On average, M.7 EMLA resulted in the largest fruit, and G.30N resulted in the smallest. Limited data will be presented on CG.6210, CG.8, G.30T, and M.26 EMLA, which are planted only at some locations. Data for the fifth season (2003) will be presented.