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  • Author or Editor: Zhiqiang Ju x
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Effects of different plant oils (soybean, corn, peanut, cottonseed, conola, sunflower, safflower, rape seed, and linseed) on mealiness, leatheriness, and flesh browning (FB) in `Elegant Lady' peaches (Prunus persica Batsch) were studied. Fruit were harvested at three dates (10 days apart) with the second harvest concomitant to commercial harvest, dipped in a 5% or 10% oil emulsion for 3 min, and stored at 0 or 5 °C, respectively. After 6 weeks at 0 °C, fruit developed more leatheriness and FB but less mealiness in early harvested compared to late-harvested fruit. When stored at 5 °C, fruit did not develop any leatheriness regardless of harvest dates, but fruit from the last harvest developed high levels of mealiness and FB compare with fruit from the other two harvests. FB was found only, but not in all, leathery or mealy fruit. None of the oils affected leatheriness, but all reduced mealiness to the same extent at the same concentration. Oil treatments controlled FB completely in both leathery and mealy fruit. Oil at 10 % was more effective in controlling mealiness and FB than at 5%. Oil-treated fruit had higher flesh firmness and titratable acidity and developed less decay than the controls at removal from storage.

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`Huangjin' peaches were harvested at immature, mature, and over-mature stages according to ground color and firmness evaluations, and were stored at 0, 5, and 10 °C, respectively. After 4 weeks of cold storage, immature fruit developed a higher percentage of leatheriness but a lower level of mealiness than mature fruit. Over-mature fruit did not develop leatheriness, but developed a higher percentage of mealiness than mature fruit. Fruit stored at 5 °C developed more mealiness than fruit stored at 0 °C for the same period of storage, while fruit stored at 0 °C developed more leatheriness than fruit stored at 5 °C. When stored at 10 °C, fruit did not develop any leatheriness or mealiness regardless of maturity. Compared with juicy and mealy fruit after the same period of cold storage, fruit with leathery symptoms were significantly firmer following 4 days at 20 °C. 1-Aminocyclopropane-1-carboxylate oxidase (ACO) activity, 1-amino-cyclopropane-1-carboxylic acid (ACC) content, and polygalacturonase (PG) and β-galactosidase (GAL) activity were lower, and insoluble pectin content was higher, in leathery fruit than that in juicy and mealy fruit. Mealy fruit were as soft as juicy fruit after ripening at 20 °C for 4 days. Their ACO, PG, and GAL activity; ACC; and insoluble pectin content were similar. Results indicated that leatheriness is a typical chilling injury but mealiness is not.

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`Feicheng' peach is a favorite cultivar in China due to is large size and high eating quality. However, its storage quality is poor and its market life is relatively short. Different combinations of AVG and GA3 applied at various stages of fruit development were evaluated to prolong market life of this fruit. A combination of 80-100 mg/L AVG and 80-100 mg/L GA3 at the end of pit hardening gave the best results. This treatment retarded the change in ground color, loss of firmness, and reduction in acidity by2 to 3 weeks. Since harvest was delayed, soluble solid content increased compared with the control that was harvested earlier. Fruit size increased significantly on treated trees. During 6 weeks of storage at 0 °C, ethylene evolution increased and fruit firmness decreased slowly in control fruit, but in AVG+GA3-treated fruit, they did not change from the low initial levels. At the end of storage, control fruit developed a high percentage (83%) of tissue browning and mealiness after warming at 20 °C for 4 days, but the AVG+GA3-treated fruit ripened normally and developed much less (16%) tissue browning and mealiness. Our results showed that the market life of `Feicheng' peaches can be prolonged by at least 4 weeks by using the AVG+GA3 treatment to delay harvest and improve storage quality.

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Effects of different plant oils (soybean oil, corn oil, olive oil, peanut oil, linseed oil, and cotton seed oil) and oil component emulsions on scald development in `Delicious' apples were studied. Prestorage treatment with commercial plant oils reduced scald development, but was not as effective as 2000 mg•L-1 diphenylamine (DPA) after 6 months of cold storage. Different oil components played different roles in affecting scald. At 6% or 9% concentrations, neutral lipids (mono-, di-, and tri-acylglycerols), and phospholipids inhibited scald to the same level of 2000 mg•L-1 DPA treatment. Free fatty acids partially reduced scald, while α-tocopherol at 3% or higher concentrations accelerated scald development. There were no differences in scald inhibition between unsaturated neutral lipids and saturated neutral lipids or among the different acylated neutral lipids. When α-tocopherol was stripped from plant oils, the stripped plant oils at 6% or 9% controlled scald to the same level of 2000 mg•L-1 DPA treatment. Emulsions of 6% or 9% neutral lipids, phospholipids, or stripped plant oils did not induce greasiness on fruit skin. Fruit treated with lipids, phospholipids, or stripped plant oils looked greener and fresher compared with the control by the end of storage.

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In China, one of the most serious problems to fruit growers is too much vegetative growth and too many pests and diseases during the growing season. Therefore, a large number of growth regulators, pesticides, and fungicides are used each year, which increases production costs and causes environmental pollution. To reduce the usage of agrochemicals, a device was invented to confine the treated area. Instead of applying chemicals directly to leaves, which may have reduced the efficiency by washing or UV degradation, the chemicals were injected directly to the truck of trees and transported through the xylem to the target organ, the leaf. Results showed that, to reach the same level of control, using plant regulators such as paclobutrazol, gibberellins, and ascorbic acid, the amount used could be reduced by 50% to 80%. The use of fungicides such as captan and diazinon could be reduced by 35% to 60%, and the use of pesticides such as vendex could be reduced by as much as 50%. Compared with the conventional method, the injection method showed three advantages: 1) It is economical in that production costs were reduced by about 40%, 2) It is efficient in that the same level of control was achieved using less chemicals (Due to the small acreage cultivated by family growers in China, the device could be installed within days and chemicals could be applied within hours.), 3) It is environmentally friendly because chemicals were not released throughout the orchard.

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Effects of 10% plant oils (corn, soybean, peanut, canola, sunflower, safflower, rape seed, linseed, and cottonseed), 100 mg·L-1 chlorine, or 100 mg·L-1 chlorine plus 10% oil combinations on pathogen (B. cinerea, P. expansum, or G. cingulata) infection and fruit decay in `Delicious' apples and `Ya Li' pears were studied. None of the oils showed inhibition on spore germination of the three pathogens by in vitro test. In inoculated fruit, oil treatments did not affect incidence but reduced severity of decay after 6 months storage at 0 °C plus 7 days at 20 °C, but no difference was found among the oils at the same concentration. In non-inoculated fruit, oils reduced fruit decay to low levels (4%) even in the most severe season. Oils also maintained fruit quality attributes, reduced water loses, and controlled scald in apples and internal browning in pears. Chlorine reduced incidence but did not reduce severity in decayed fruit. Fruit first drenched with chlorine then dipped in oil emulsions without pathogen inoculation remained decay free, while control fruit developed 10% to 15% or 13% to 23% decay after 6 months at 0 °C plus 7 days at 20 °C in both apples and pears, respectively.

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Preclimacteric `Bartlett' pears (Pyrus communis L.) were dipped for 3 min in either corn (Zea mays L.) or soybean [(Glycine max (L.) Merrill] oil emulsion immediately after harvest and stored at 0 °C. Untreated control fruit developed higher percentages of senescent scald, core breakdown, and decay after 15 weeks storage. Both treatments inhibited senescent scald, core breakdown, and decay in a similar and concentration dependent manner. Complete control of senescent scald and core breakdown was achieved by emulsions at 5% and 10%, and of decay by emulsion at 10%. Compared with controls, emulsion treatments delayed and reduced internal ethylene accumulation and volatile production in early storage and increased them in late storage. Compared with controls, fruit treated with oil contained similar levels of internal O2 and CO2 in early storage and higher CO2 and lower O2 in late storage. While control fruit lost commercial value after 15 weeks at 0 °C plus 5 days at 20 °C, oil-treated fruit exhibited normal color change, and had higher soluble solids, titratable acidity, and volatile production. Microscopic examination revealed that emulsion-treated fruit had a continuous surface film conforming to the contour of the fruit.

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A full-length cDNA isolated from banana (Musa acuminata L. AAA group) fruit was named MaMDH, containing an open reading frame encoding 332 amino acids that represents the gene for cytoplasmic malic dehydrogenase (MDH). Sequence analysis showed that MaMDH shares high similarity with MDHs from castor bean (XP_002533463), tobacco (CAC12826), peach (AAL11502), and chickpeas (CAC10208). Real-time quantitative polymerase chain reaction (PCR) analysis of MaMDH spatial expression showed that it was expressed in all organs examined: roots, rhizomes, leaves, flowers, and fruits. The expression was the highest in flowers followed by the fruits and roots, whereas the rhizomes and leaves displayed the lowest expression levels. Real-time quantitative PCR revealed that MaMDH exhibited differential expression patterns in post-harvest banana fruits correlating with ethylene biosynthesis. In naturally ripened banana fruits, MaMDH expression was in accordance with ethylene biosynthesis. In accordance, for banana fruits treated with the ethylene analog 1-methylclopropene (1-MCP), MaMDH expression levels were inhibited and remained constant. After treatment with ethylene, MaMDH expression in banana fruits significantly increased with ethylene biosynthesis and peaked 3 days after harvest, which was 11 days earlier than that in naturally ripened banana fruits. These results suggest that MaMDH expression is induced by ethylene to regulate post-harvest banana fruits ripening.

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The banana, a typical climacteric fruit, undergoes a postharvest ripening process followed by a burst in ethylene production that signals the beginning of the climacteric period. Postharvest ripening plays an important role in improving the quality of the fruit as well as limiting its shelf life. To investigate the role of glutamate decarboxylase (GAD) in climacteric ethylene biosynthesis and fruit ripening in postharvest banana, a GAD gene was isolated from banana, designated MuGAD. Coincidently with climacteric ethylene production, MuGAD expression as well as the expression of the genes encoding the Musa 1-aminocyclopropane-1-carboxylate synthase (MaACS1) and Musa 1-aminocyclopropane-1-carboxylate oxidase (MaACO1) greatly increased during natural ripening and in ethylene-treated banana. Moreover, ethylene biosynthesis, ripening progress, and MuGAD, MaACS1, and MaACO1 expression were enhanced by exogenous ethylene application and inhibited by 1-methylcyclopropene (1-MCP). Taken together, our results suggested that MuGAD is involved in the fruit ripening process in postharvest banana.

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