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Zhiguo Ju

Three years of experiments were carried out with both Delicious fruit on trees and fruit skin discs. There were two peaks of phenylalanine ammonia lyase (PAL) activity during fruit development. One occurred in the fruitlet stage and the other in the fruit enlargement stage. The first peak was coincident with anthocyanin synthesis in fruitlet but the second peak did not correlate with pigment formation during maturation. In fact, PAL activity decreased gradually during fruit maturation and coloration. Treatment with L-α-aminooxy-B-phenylpropionic acid, a specific PAL inhibitor, decreased PAL activity in fruit and in skin discs 57% and 80%, respectively, but did not change anthocyanin content. Cycloheximide inhibited anthocyanin synthesis by 76% in fruit and 85% in skin discs, but did not significantly inhibit PAL activity. On the other hand, PAL activity was positively correlated with concentrations of simple phenols which were direct products of PAL and precursors for synthesis of lignin, anthocyanin and other flavonoid.

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Zhiguo Ju

Delicious apples were harvested and analyzed every 7 days from the start of fruit coloration to commercial harvest. Chalcone synthase (CS) activity increased from 521 to 4120 fkat/g protein during 30 days, while UDPG glucosyltransferase (UDPGTF) activity increased from 0 to 6570 fkat/g protein. These changes significantly correlated with anthocyanin synthesis in fruit skin. Ethephon enhanced activities of both enzymes for 25 days after application, but not beyond. Cycloheximide inhibited CS and UDPGTF activities by 57% and 72%, respectively, and this could not be overcome by ethephon treatment. Bagging prevented fruit from coloring, and removing bags before maturation promoted it. Activity of both enzymes was nil in bagged fruit, and increased dramatically after bag removal. Cycloheximide applied at bag removal reduced CS and UDPGTF activities 74% and 91%, respectively, and decreased anthocyanin synthesis by 82%. The results showed that both CS and UDPGTF were positively correlated with anthocyanin formation and both required de novo synthesis during fruit coloring, although CS had existed before that.

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Zhiguo Ju, Yousheng Duan and Zhiqiang Ju

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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Zhiguo Ju, Yousheng Duan and Zhiqiang Ju

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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Zhiguo Ju, Yousheng Duan and Zhiqiang Ju

`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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Zhiguo Ju, Yousheng Duan and Zhiqiang Ju

`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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Yousheng Duan, Zhiqiang Ju and Zhiguo Ju

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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Zhiguo Ju and Eric A. Curry

At harvest, internal ethylene was >0.5 mL·L–1 and α-farnesene concentrations were below detectable levels in `Golden Supreme', `Delicious', and `Granny Smith' apples. After 30 days of storage at 20 °C, control fruit produced high levels of internal ethylene and α-farnesene. Lovastatin at 100 to 1000 mL·L–1 did not affect ethylene synthesis, but significantly inhibited α-farnesene production. In `Golden Delicious', ethephon treatment increased ethylene synthesis in lovastatin-treated fruit but did not stimulate α-farnesene production. In lovastatin-treated fruit peel of `Delicious' and `Granny Smith', mevalonate (MAL) and farnesyl pyrophosphate (FPP) induced α-farnesene production, but hydroxymethylglutaric acid (HMG) did not. The induction of α-farnesene synthesis by MAL and FPP was concentration-dependent. Precursor feeding did not affect ethylene production in fruit peel. When high level of α-farnesene was detected in fruit peel (5 mm thick), it was not found in outer (adjacent to peel) and inner cortex (mid of flesh) tissues. Adding HMG, MAL, and FPP induced α-farnesene biosynthesis in both cortex tissues. When lovastatin was added to the feeding solution, MAL and FPP induced α-farnesene production but HMG did not.

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Zhiguo Ju and Eric A. Curry

`Granny Smith' apples (Malus × domestica Borkh) and `d'Anjou' pears (Pyrus communis L.) were dipped in a 2.5%, 5%, or 10% stripped corn oil (α-tocopherol <3 mg·kg-1) emulsions, 2000 mg·L-1 diphenylamine (DPA), respectively, at harvest and stored in air at 0 °C for 8 months. Untreated fruit served as controls. In oil-treated apples and pears, ethylene and α-farnesene production rates were lower in early storage and higher in late storage than in control. Control fruit developed 34% scald in `Granny Smith' apples and 23% scald in `d'Anjou' pears after 6 months storage, whereas fruit treated with oil at 5% or 10%, or with DPA at 2000 mg·L-1 were free from scald. After 8 months storage, oil at 10% was as effective as DPA in controlling scald in pears, whereas in apples, fruit treated with 10% oil developed 18% scald and DPA-treated fruit were scald-free. DPA-treated apples developed 32% senescent scald, while 5% or 10% oil-treated fruit had none. Oil-treated fruit were greener, firmer, and contained more titratable acidity after 8 months of storage than control or DPA-treated apples and pears. In `Granny Smith', 100% of the controls and 79% of the DPA-treated fruit developed coreflush after 8 months of storage, but both 5% and 10% oil-treated fruit were free from coreflush. In `d'Anjou', 34% of the controls and 27% of the DPA-treated fruit showed decay after 8 months of storage, compared with 5% decay in 5% oiltreated fruit, and no decay in 10% oil-treated fruit.

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Zhiguo Ju and Eric A. Curry

Effects of Lovastatin treatment on ethylene production, α-farnesene biosynthesis, and scald development were studied using `Delicious' and `Granny Smith' apples and `d'Anjou' pears stored in air at 0 °C. During 6 months of storage, Lovastatin did not affect internal ethylene concentration, but reduced α-farnesene production in a concentration-dependent manner in both apples and pears. Lovastatin reduced scald at 0.63 mmol·L-1 and inhibited scald completely at 1.25 or 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. In `d'Anjou' pears, Lovastatin at concentrations from 0.25 to 1.25 mmol·L-1 inhibited scald completely. After 8 months of storage, the inhibition of scald in both apples and pears by Lovastatin was concentration-dependent, but none of the concentrations eliminated scald. Compared with 11.8 mmol·L-1 diphenylamine (DPA), Lovastatin treatment reduced scald to the same level at 1.25 mmol·L-1 in `d'Anjou' pear and 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. Compared to the controls, Lovastatin did not affect fruit color, firmness, soluble solid contents, or titratable acidity during storage in either apple or pear.