Search Results

You are looking at 11 - 16 of 16 items for

  • Author or Editor: P.M. Chen x
Clear All Modify Search

Abstract

Low temperatures (LT) exotherms were found by differential thermal analysis (DTA) at −30°C in ‘Siberian C’ peach (Prunus persica [L.] Batsch) and −39° in ‘Starkrimson Delicious’ apple (Malus domestica Borkh. Nuclear magnetic resonance (NMR) spectrometry of intact stems and isolated bark and wood revealed that the LT exotherm was produced by freezing of deep supercooled water which was detected in the wood but not the bark. Freezing processes of the wood and bark appeared to be independent. In both species, xylem injury occurred at the same temperature as the LT exotherm and was closely, if not causally related to freezing of the supercooled water. Bark injury also occurred at the same temperature as the LT exotherm and may have been caused by dehydration stress or freezing of a small amount of supercooled water which remained undetected by NMR spectrometry. The dehydration resistance of apple wood on desiccation at 70 to 90% relative humidity was greater than that of the peach wood which in turn was greater than that of the bark of both species. The dehydration resistance of apple and peach wood may involve both nonliving and living elements of the wood because pulverizing the tissue destroyed the effect, whereas heat killing only lowered it. Both supercooling and dehydration resistance may be related to microcapillary pore structure which restricts heterogeneous nucleation and sublimation of supercooled water from the ray parenchyma cells.

Open Access

Abstract

‘Bose’ pear fruits (Pyrus communis L.) grown in northern Oregon (NO, Hood River) and southern Oregon (SO, Medford) were harvested during the commercial harvest period and stored in either 1 % O2 with trace CO2 or in 5 other controlled atmosphere (CA) regimes, O2/CO2 at 0.5%/0%, 1.0%/0.5%, 1.5%/0.5%, 2.0/0.5%, and 2.5%/1.0%, for 6 months at −1°C in 1982, 1983, and 1984. Fruits from the NO were more susceptible to brown core (BC) disorder than those from SO. Late-harvested fruits, especially from NO, were more susceptible than early harvested ones. A low O2 concentration of <1% in CA storage without CO2 increased the potential for fruit to develop BC, and an elevated CO2 level enhanced the effect of low O2. Based on this study, it is recommended that ‘Bose’ pear fruits from NO can be safely stored in O2 not less than 1.5% with trace CO2 and those from SO in O2 as low as 1% with CO2 between 0 and 0.5% for 6 months at −1° with little probability of BC.

Open Access

Abstract

Ethylene production of ‘Bartlett’ pears (Pyrus communis L.) was suppressed by 1 % O2 during storage at − 1°C. Elevated CO2 concentrations further suppressed ethylene production. Organic acids were retained at higher levels in fruits stored in 1% O2 than in those stored in air, and elevated CO2 concentrations in 1% O2-enhanced acid retention. Both malic and citric acids decreased linearly during 8 days of ripening at 20° regardless of previous storage conditions. The suppression of ethylene production and the retention of organic acids implied a beneficial effect of elevated CO2 in storage of ‘Bartlett’ pears at 1% O2. Fruit stored in 1% O2 at −1° for 4 months developed brown-core regardless of CO2 levels in the storage, but the incidence of the disorder was enhanced when CO2 level in the storage was ≥2%. This preliminary study indicated that ‘Bartlett’ pears grown in the Hood River district of Oregon could be stored at −1° for 4 months in 1% O2 with CO2 at <1.5% with a minimum risk of brown-core development.

Open Access

Abstract

‘Bing’ sweet cherries (Prunus avium L.) harvested at commercial maturity were commercially packed and stored in 6 low-02 and 1 high-C02 controlled atmospheres (CA) at −1.1°C for 35 days and in a second study were stored in either 1.5% 02 and 0.8% C02 or 12% 02 and 10% C02 at 5.6°, 3.3°, or 1.1°C for 23 days. Fruit stored at 0.5–2.0% 02 with 0.03% C02 maintained a higher percentage of very green stems, brighter fruit color, and higher levels of titratable acids than those stored in air at −1.1°C for 35 days. High C02 atmospheres conserved fruit brightness and TA level but did not prevent stem discoloration. The only effect of lowering temperature from 5.6° to 1.1° was a slight increase in fruit firmness after storage.

Open Access

A proportion of `d'Anjou' pear fruit (Pyrus communis L.) developed a disorder, “black speck” or “skin speckling”, after prolonged controlled atmosphere (CA) storage (1% O2, - 0.5 C). A comparative study of biochemical components revealed that there was no significant difference in succinic, citric, fumaric, and pyruvic acids between the speckled' and normal skin tissues. The content of malic acid in the affected tissue was almost three times lower than that in the normal tissue. The specific activity of NADP-malic enzyme (EC 1.1.1.40) in the affected tissue was also lower, but the total activities were similar. The affected tissue contained higher percentages of dry matter and soluble proteins than the normal tissue. Two-dimensional gel electrophoresis of proteins showed that two groups of novel polypeptides appeared only in the affected skin tissue. This study indicated that a certain proportion of `d'Anjou' pear fruit might have been exposed to unfavorable preharvest environmental stresses, and, therefore, could no longer tolerate the subsequent semi-anaerobic and chilling stresses during prolonged CA storage.

Free access

Seed germination patterns were studied in Echinacea purpurea (L.) Moench grouped by seed source, one group of seven lots from commercially cultivated populations and a second group of nine lots regenerated from ex situ conserved wild populations. Germination tests were conducted in a growth chamber in light (40 μmol·m–2·s–1) or darkness at 25 °C for 20 days after soaking the seeds in water for 10 minutes. Except for two seed lots from wild populations, better germination was observed for commercially cultivated populations in light (90% mean among seed lots, ranging from 82% to 95%) and in darkness (88% mean among seed lots, ranging from 82% to 97%) than for wild populations in light (56% mean among seed lots, ranging from 9% to 92%) or in darkness (37% mean among seed lots, ranging from 4% to 78%). No germination difference was measured between treatments in light and darkness in the commercially cultivated populations, but significant differences were noted for treatments among wild populations. These results suggest that repeated cycles of sowing seeds during cultivation without treatments for dormancy release resulted in reduced seed dormancy in E. purpurea.

Free access