Effects of harvest time and fruit bagging treatments on the fruit quality of‘Red Fuji’grown in the cold highland in southwest China

Abstract: 【Objective】Zhaotong municipality is a apple-producing area, covers mostly the flatland of Zha⁃oyang and Ludian. The annual average temperature in this area is 11.7 ℃, with a low annual range but ahigh daily range. The accumulated temperature greater than or equal to 10 ℃ in this area is 3 237-3 477 ℃. The climate is of the central temperate climate, with annual sunshine of 1 916.7 h, 230-240frost-free days, and an annual average rainfall of about 740 mm. With a cultivation history of 76 years,Zhaotong is now the largest high quality apple region in southern China. The successful cultivation of ap⁃ple in Zhaotong proves that fruits in Northern China can also be cultivated in Southern China. With theintroduction of apple cultivation to the southwest of China, the high altitude and cool temperature proveto be advantageous for apple cultivation and the development of apple cultivation will play a more impor⁃tant role in local economic construction. Because of history and tradition, apple cultivation technologyand research in our country is mainly based on that in the north. Reports about apple cultivation in thewest and the southwest are not frequently seen, and there has no reports about the internal quality of theapples produced in areas of high altitude and cool temperature in southwest China. This study evaluatesthe influence of harvesting time and bagging treatments on the quality of apple, so as to provide referencefor apple cultivation in areas with high altitude and cool temperature.【Methods】‘Red Fuji’apple weresampled from orchards that are typical of the area. Traditionally,‘Red Fuji’apple in Zhaotong are harvested for three times, the early September, around October 1st (around the Mid-Autumn Festival), andthe early to mid October. We collected bagged fruit and unbagged fruit 15 days before each traditionalharvest time for quality analysis. Since the socalled“sugar-cored”apple fruit are populous among consumers, we also took fully mature un-bagged fruit samples in the late October and the early November.Our analyses included fruit maturity, fruit hardness, soluble solid contents, soluble sugars, titratable acids, vitamin C and moisture, and soluble solid to acid ratio. The mathematical statistics method was usedto analyze the fruit quality and the advantages of apple produced in Zhaotong with the reference of“Fresh Apple Fruit Standard”. Based on the analyses, we could determine the critical time for commercial harvest, the physiological mature time, and the harvest time with the best eating quality.【Results】Bagged fruit and unbagged fruit picked at the same time were different in quality parameters. The ratio oftotal soluble solid content to acidity of the bagged fruit was lower than that of the unbagged ones. As faras internal quality and taste were concerned, the unbagged fruit were better than the bagged ones. Thematurity degree of unbagged fruit harvested from September 7 to October 14 increased from 7.67 to 9, and soluble solids and vitamin C increased as harvest was postponed. At the same time, the fruit moisturecontent declined slightly, while titratable acids remained relatively constant. Vitamin C increased consid⁃erably and fruit hardness decreased significantly when the harvest time was postponed. From September7 to October 14, the maturity degree of bagged fruit increased from 7.73 to 9.33 and fruit hardness de⁃creased from 9.03 kg·cm-2 to 8.26 kg·cm^-2. Soluble solid content increased between the first two harvesttimes but decreased before the last harvest time. In a certain period, the taste was better in fruit harvested later. In the early September, fruit were mature enough for early commercial harvest; in the early October, the fruit were of good eating quality; and in the mid October, they were physiologically fully mature.Because bagging treatment changed the growing environment of apple fruit, maturation was advanced byone week. The average contents of soluble solids and soluble sugars in unbagged fruit reached up to 16%and 15%, respectively, and the ratios of total soluble solids to acidity and soluble sugar to acidity reached56.11 and 54.49 respectively in the period from the late October to the mid November. During this period,“sugared core”developed in apple fruit and such fruit were of the best taste. Thus, this period wasthe best harvest time for fresh consumption.【Conclusion】Bagged and unbagged‘Red Fuji’apple produced in the cold highland in southwest China have a good internal quality when they are harvested atcommercial maturity. In order to reduce cost and protect environment, bagging treatment can be abandoned. After full physiological maturity, due to the high altitude, low latitude, and cool weather condition,the so-called“sugar core”apple are produced. Such a kind of fruit are of the best eating quality and thisis worthy of further study.