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Allan B. Woolf and Michael Lay-Yee

`Hass' avocados [Persea americana Mill.] were pretreated in water (38 °C for up to 120 min) immediately before 50 °C hot water treatments of up to 10 min. Fruit were stored for 1 week at 6 °C and ripened at 20 °C. External browning was evaluated immediately upon removal from cold storage, and fruit quality evaluated when fruit were ripe. Pretreatments at 38 °C tended to reduce the levels of external browning, skin hardening, and internal disorders, such as tissue breakdown and body rots, that were associated, and increased, with longer hot water treatments. A pretreatment of 60 min was the most effective for eliminating external browning, and reducing hardening of the skin when fruit were ripe following hot water treatment. Examination of heat shock protein (hsp) gene expression in avocado skin tissue, showed that levels of hspl7 and hsp70 homologous mRNA increased with increasing pretreatment duration. The results demonstrate that 38 °C pretreatments increase the tolerance of avocado fruit to subsequent hot water treatments.

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M. López-Serrano and A. Ros Barceló

Levels and histochemical localization of peroxidase and polyphenol oxidase, and levels of anthocyanins and (+)-catechin, were studied in fruit of two strawberry (Fragaria ×ananassa Duch.) cultivars (`Oso Grande' and `Chandler'), which show different degrees of susceptibility to enzymatic browning after processing. Although the levels of anthocyanins at the processing-ripe stage may be important in determining pigment stability, and therefore market suitability, the color stability of `Chandler' is apparently determined by the lower endogenous levels of peroxidase and polyphenol oxidase in the processing-ripe stage, which are also accompanied by a lower (+)-catechin content. Polyphenol oxidase was localized almost exclusively in the cortex and to a lesser extent in the pith, showing a complementary pattern to that shown by peroxidase, which was localized in the vascular bundles. Since peroxidase and polyphenol oxidase showed a complementary localization pattern in the fruit, these results strongly suggest a synergic role for these two oxidative enzymes in pigment decay and the associated browning reaction, which occurs in processed strawberry fruit and their derived foods.

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Dangyang Ke, Leonor Rodriguez-Sinobas, and Adel A. Kader

Fruits of `Granny Smith' and `Yellow Newtown' apples (Malus domestica Borkh), `20th Century' pear (Pyrus serotina L.), and `Angeleno' plum (Prunus domestica L.) were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10C for 3, 7, 14, 25, or 35 days to study the effects of low-O2 atmospheres on their postharvest physiology and quality attributes. Soluble solids content (SSC), pH, and external appearance were not significantly influenced, but resistance to CO2 diffusion was increased by the low-O2 treatments. Exposures to the low-O2 atmospheres inhibited ripening, including reduction in ethylene production rate, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. The most important detrimental effect of the low-O2 treatments was development of an alcoholic off-flavor that had a logarithmic relation with ethanol content of the fruits. The ethanol content causing slight off-flavor (Eo) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula: (Log Eo)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (VE) from each low-O2 treatment, the tolerance limit (Tl) of fruits to low-O2 atmospheres could be predicted as follows: Tl = Eo/VE = (100.228SSC)/VE.

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Rafael Alique, José P. Zamorano, Ma Luisa Calvo, Carmen Merodio, and José L. De la Plaza

`Fino de Jete' cherimoya fruit were stored at 20, 10, 8, or 6C, 80% relative humidity. Two rises of CO2 production and an ethylene rise following the first peak of respiration were obtained in fruit held at 20C. The ripe stage coincided with the onset of the second respiratory rise. Soluble sugar and organic acid concentration were maximal, and flesh firmness was 18 N in ripe fruit. Lower temperature reduced respiration rate and ethylene production; however, some stimulation of ethylene synthesis was observed at 10C. Cherimoyas ripened to edible condition during 6 days at 10C, but fruit maintained at 8C for up to 12 days required transfer to 20C to ripen properly. Our results suggest that high increases in CO2 are not sufficient to complete cherimoya fruit ripening without the concurrent rise in ethylene production. Citric acid accumulation, inhibition of ethylene synthesis, and reduced accumulation of sucrose were observed during storage at 6C. Removal to 20C after 12 days at 6C resulted in no ripening, almost complete inhibition of ethylene synthesis, and severe skin browning. Thus, 8C is the lowest tolerable temperature for prolonged cold storage of cherimoya `Fino de Jete'. Fruit can be held at 8C for up to 12 days without damage from chilling injury.

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Karim M. Farag and Jiwan P. Palta

A natural lipid, lysophosphatidylethanolamine (LPE), was used as a tomato fruit ripening agent. The effect of this compound on hastening the ripening and on the defoliation of the `Heinz 7155' processing tomato and the Glamour fresh-market tomato (Lycopersicon esculentum Mill.) was compared to the effect of ethephon. Vines were sprayed to runoff in the field with a hand sprayer and fruits were harvested 2 weeks or 20 days later in a single harvest operation. LPE (100 mg liter-1) accelerated ripening of both processing and fresh-market tomatoes without defoliation. LPE-treated tomatoes had a better shelf life than the control or ethephon-treated fruit, whether they were harvested at the breaker, pink, or red stage of maturity. The combination of LPE and ethephon (100 mg liter-1) enhanced tomato ripening without damaging the foliage, suggesting that LPE can mitigate the undesirable effects of ethephon on foliage and the fruit. The LPE-related lipid phosphatidyldimethylethanol-amine dipalmitoyl (PDED) also was able to enhance some aspects of keeping quality of tomato fruits, but was not able to enhance fruit ripening. Phosphatidylethanolamine was not as effective as LPE or PDED. It appears that the active molecule of this natural lipid is the lyso form. Our results provide evidence that LPE can enhance tomato fruit ripening and postharvest storage life of vine-ripe fruits and fruits picked at early ripeness stages.

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Ann M. Callahan, Peter H. Morgens, and Reuben A. Cohen

Peach [Prunus persica (L.) Batsch] cDNA libraries have been constructed from RNA isolated from immature (30 days after bloom) and ripe fruit. cDNA clones of interest have been identified by differential hybridization among the cDNAs of various peach cultivars or from several stages in fruit development. In addition, several clones were isolated by low stringency hybridizations with oligonucleotides derived from a tomato polygalacturonase cDNA sequence and a cucumber peroxidase amino acid sequence. The pattern of accumulation of the corresponding mRNAs during fruit development was examined by RNA gel-blot analyses in the commercial cultivar Suncrest. Three cDNA clones, pch201, pch307, and pch313, were related to mRNAs that accumulate during the softening stage of fruit development. cDNA clones pchl03, pch205, and pch306 were related to an mRNAs that increase in abundance throughout development, with maximum levels in ripe fruit. cDNA clones pch104 and pch202 were related to mRNAs that exhibit maximum abundance in midfruit development, and clone pch108 was related to mRNA that decreases as the fruit matures. Southern analyses indicated that seven of the cDNAs are represented by only a few genes, while pch104 detects a repetitive family, and pch307 detects a small family of genes. These clones will provide the initial source of genes to manipulate and affect fruit development.

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A. Raymond Miller, Joseph C. Scheereus, Patricia S. Erb, and Craig K. Chandler

A tissue culture protocol was developed that increased the germination percentage and decreased the lag time to germination for strawberry (Fragaria x ananassa Duch.) achenes. This technique involved cutting surface-sterilized achenes across the embryo axis then placing the shoot apex/radicle-containing sections on semisolid Murashige and Skoog medium lacking hormones. Cut achenes began germinating 5 days after culture and achieved maximum germination (97% to 100%) in less than 2 weeks, compared to whole achenes, which began to germinate 7 to 10 days after sowing and required more than 7 weeks for maximum germination (<50%). Enhanced germination of cut achenes was a general phenomenon since achenes from 231 hybrid crosses responded similarly. Following placement on culture medium, cut achenes could be stored up to 8 weeks at 4C then removed to 27C, where germination and seedling development occurred at percentages and rates comparable to freshly cut achenes. Achenes did not require stratification before cutting to exhibit increased germination. Nearly 100% of the achenes from freshly harvested red-ripe, pink and white strawberries germinated after cutting and culture, although cut achenes from white and pink berries germinated more slowly than those from red-ripe berries. Achenes from green berries, whether whole or cut, did not germinate. This method of “embryo rescue” could be used to generate more seedlings from poorly germinating hybrid crosses, would considerably decrease the time from sowing to seedling production compared to traditional means, and would produce seedlings of uniform age for subsequent field evaluation.

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Guiwen W. Cheng and Patrick J. Breen

Studies on regulation of production of phenolics in strawberry (Fragaria X ananassa Duch,) fruit were initiated by monitoring phenylalanine ammonia-lyase (PAL) activity and levels of anthocyanins, flavonoids, tannins, and other soluble phenols throughout fruit ontogeny in `Tillikum'. PAL catalyzes the first step in the biosynthesis of phenylpropanoids, which are further modified into a wide variety of phenolic compounds. Peak in PAL activity (1 mol· s-1 = 1 kat) of 90 pkat· mg-1 protein was detected at 5 and 27 days after anthesis (DAA), when fruit was green and nearly ripe, respectively. PAL activity was only ≈10% of peak values in the white berry stage, when. fruit growth was most rapid. The second peak in PAL activity was followed by a rapid drop, to nearly zero in red-ripe fruit at 30 DAA. Total soluble phenols reached a maximum level soon after anthesis, just before the first peak in PAL activity, then declined to a low constant value well in advance of fruit ripening. Similar changes were observed in levels of tannins and flavonoids that, at anthesis, accounted for 44% and 51% of the soluble phenols, respectively. The concentration of anthocyanin was very low throughout most of fruit development, but beginning at 23 DAA it increased from <0.03 to >0.53 mg·g-1 fresh weight in 3 days. This accumulation paralleled the second rise in PAL activity. Accordingly, strawberry fruit have a developmental-dependent expression of PAL activity and accumulation of phenolic substances derived from the phenylpropanoid pathway.

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Anatoliy Kucher and Raymond L. Granger

`Platonivs'ka' has been released as a new autumn pear cultivar that combines scab (Venturia pirina Aderh.) resistance and cold hardiness under Ukrainian climate and soil conditions, selected from a cross of `Hybrid 1931' (`Oleksandrivka' × `Dekanka du Comice') × Beurré Bosk. The trees grow vigorously, are adequately winter-hardy, and resistant to both leaf and fruit scab. Very good tree productivity has been observed when `Platonivs'ka was grafted on Limonska Oleksandrivka, Wild Forest Pear, Quince A, or BA-29 rootstocks. The fruit attains its picking ripeness between 10 and 20 Sept. (2 weeks after `Bartlett') and eating ripeness between the beginning and end of October in Ukraine. Its storage life at 0 to 2C lasts until the end of January. The average weight per fruit ranges between 180 and 200 g (70–75 mm in diameter). The fruit eating quality is excellent; its juicy and pleasant sugar/acid ratio makes it a very good dessert pear. Fruits are ovatepyriform in shape. Their skin color is light grayish-green and their finish is glossy at harvest. Flesh texture is moderately find and buttery. At harvest, grit cells are small and evenly distributed in the flesh and they become inconspicuous when the fruit is held at 20C for a week. `Platonivs'ka' is recommended for both home and commercial orchards.

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David Wees

`Caruso' tomatoes were grown in a glass greenhouse in Winter and early Spring 1991. All plants were grown in 16-liter nursery pots. Half the plants were grown in a conventional peat-lite medium (Profi-mix) and were fertilized with synthetic water-soluble fertilizer containing micronutrients and (in ppm) 187 N, 46 P, 278 K, 177 Ca, and 48 Mg. The other plants were grown in a potting medium composed of 1 mature compost (chicken manure and leaves): 1 loam: 2 vermiculite (by volume); this medium was amended with 1.5 kg bone meal (2N–10P–0K) and 3 kg dolomitic lime/m3. The “organic” treatment was fertilized with a fish emulsion solution containing (in ppm) 150 N, 13 P, and 25 K. The experiment was repeated in 1992 with `Capello'. In both years, fruit were harvested around the half-ripe to three-quarters ripe stage. All insect control was with insecticidal soap and bio-control agents. A blind taste test was conducted on campus in both years. In 1991, of 70 participants, 73% preferred the “conventional” tomatoes, 20% preferred the organic tomatoes, and 7% expressed no preference. In 1992, of 105 participants, 67% preferred the “conventional” tomatoes, 24% preferred the organic tomatoes, and 10% expressed no preference.