Effect of Maturity Stage on the Gene Expression of Antioxidative Enzymes in Cucumber (Cucumis sativus L.) Fruits Under Chilling Stress

The gene expression pattems of antioxidative enzymes in cucumber （Cucumis sativus L.） fruits at four different maturity stages, immature （3-8 d after anthesis （DAA）, mature （9-16 DAA）, breaker （17-22 DAA）, and yellow （35-40 DAA）, were determined before and after cold storage at 2℃ for 9 d and after subsequent rewarming at 20℃ for 2 d. The electrolyte leakage and malondialdehyde content in cucumber fruits were increased after cold storage and subsequent rewarming. Increased expressions of peroxidase, ascorbate peroxidase （APX）, and monodehydroascorbate reductase after cold storage played an important role in cucumber fruits to cope with chilling injury. The elevated cyt-superoxide dismutase, catalase, APX and dehydroascorbate reductase after subsequent rewarming in cucumber fruits facilitated the recovery from chilling stress. The highest expression levels of all the seven antioxidative enzyme genes in yellow fruits might be responsible for the enhanced chilling tolerance. Cucumber fruits at earlier developmental stages was more susceptible to chilling stress than those at later stages. The relative higher gene expressions of antioxidative enzymes genes at earlier developmental stages may be the responses to the sever oxidative stress caused by chilling injury.

Effects of maturity of citrus fruits on their stalks cutting force

When the citrus harvesting robot harvests citruses,the mechanical properties of citrus stalks have an important influence on the success rate of the citrus harvesting robot.During the harvesting,the maturity of citrus fruits not only determined the harvesting time of citrus fruits but also affected the mechanical properties of citrus fruit stalks.In this study,the changes in the cutting force of citrus fruit stalks were described during the maturity of citrus fruits,and the effect of the maturity on the cutting force of stalks was clarified,so as to determine the harvesting time with the minimum cutting force required for harvesting citrus fruits by the harvesting robot.During the maturity,the relevant parameters of fruit maturity,such as the hardness,pH,and solid solution content of citrus fruits,were monitored.The results showed that there is a significant correlation between the hardness,pH,the solid solution content of citrus fruits,and the cutting force of citrus fruit stalks during maturity.The single-factor mechanical model of hardness,pH,solid solution content of citrus fruits,and the cutting force of citrus fruit stalks were established based on the data of 2019,which were verified through tests in 2020.The test results are as follows:during the ripening period of citrus fruits,the fruit hardness varies in the range of 0.13-0.31 MPa,the hardness changes by 0.02 MPa,and the cutting force changes by about 2.0-6.0 N;the pH of the citrus fruits changes in the range of 2.8-4.0,and the cutting force changes by about 1.5-2.2 N for every 0.1 change in the pH;the variation range of fruit solid solution content is 6.5%-9.0%,and for every 0.2%change in solid solution,the cutting force of citrus fruit stalks changes by about 1.25-2.0 N.The mechanical models can predict the cutting force required to cut off citrus fruit stalks according to the relevant parameters of citrus fruit maturity and can provide a reference for effectively evaluating the required cutting force.

Comprehensive evaluation of Korla fragrant pears and optimization of plucking time during the harvest period

To optimize the harvest of Korla fragrant pears and to provide a theoretical basis for post-harvest processing,a total of 26 basic indices of Korla fragrant pears,including their morphology,quality,and softening age,were investigated.The harvest period ranged from August 22nd to October 6th,samples were collected every 5 d(totally 10 plucking days,indicated as H1-H10).The results indicated that changes in pectin content were the main causes of softening in fragrant pears.The scavenging of free radicals mainly occurred because of the collaborative effects of superoxide dismutase(SOD)and catalase(CAT).In the harvest periods H1-H3,the hardness,titratable acid(TA),chlorophyll content,density,and diameter of the stone cells,as well as the cellulose and hemicellulose content of the Korla fragrant pears were at their highest.During the periods H7-H10,the single-fruit weight,fruit horizontal and vertical diameter,color coordinates L,a*,b*,soluble-solids content(SSC),SOD activity,CAT activity,and water-soluble pectin were higher than in the other plucking periods.The highest vitamin C(VC)content and moderate values for a variety of indicators were observed during H3-H7.Variations in the Korla fragrant pears during H1-H3 mainly manifested through changes in softening-related parameters.During H3-H10,changes in the softening-related,aging-related,color-related,and quality indices had a dominant role.On this basis,some suggestions for the post-harvest processing of fragrant pears have been proposed.Fruit,during H1-H3,are suitable for transportation and storage;during H7-H10 are suitable for fresh-eating and further processing;and during H3-H7,exhibited moderate values for a variety of indicators and had the highest commercial value.This research provides a systematic evaluation of the characteristics of mature Korla fragrant pears during the harvest period and can form the basis for fruit quality control and processing of Korla fragrant pears.