Effect of different chill-proof measures on fruit quality and input-output benefits in loquat

Abstract: 【Objective】Loquat production shows a very thriving prospect in the agricultural industry, which possesses economical, social and commercial values in Guizhou. However, in the process of growth and development, loquat is frequently subjected to a series of adversity, such as freezing, extreme temperature injury, etc., leading to a serious decline on the yield and quality. Hence, it's crucial to develop a set of high quality and efficient cultivation technology for loquat. The purpose of this study was to screen out the optimal antifreezing measures by comparatively investigating the effect of different chill-proof measures on fruit setting, fruit size and quality, fruit weight and yield, and input-output ratio. It can not only improve the profits of orchardists effectively, but also dramatically promote the expansion of loquat industry.【Methods】The experiment was carried out on the subtropical plateau monsoon climate, where the altitude is around 900 m and the annual temperature is about 15.3 ℃, and the frost free days are approximately 276. Eight-year-old loquat trees of‘Qianxing'cultivar were used as materials, which were planted at a spacing of 4.0 m×4.0 m and grew to the height of 2.5-3.0 m. The soil was sandy loam with good water holding capacity, well drained, moderate soil fertility and soil pH of6.0. In the experiment, seven chill-proof measures were applied, including cold-proof cloth, aluminum foil bag, nonwoven fabric, sunshade, anti-freezing chemicals, plastic steel frame greenhouse and arch bar skeleton with polyethylene film. And those measures were applied before the chilling temperatures occurred. Moreover, the anti-freezing chemicals were sprayed twice or three times at 10:00 am on a sunny day before and after the chilling occurred. Each chill-proof measure was set in three experimental plots (three repetitions) , and each of the plot was selected randomly with three moderate vigor trees planted in a continuous row. After flower thinning, four hundred and fifty fruit clusters were retained per plot. Moreover, for each fruit cluster five fruits were reserved after fruit thinning before chilling occurred. The fruit setting ratios with four kinds of chill-proof measures including aluminum foil bag, arch bar skeleton with polyethylene film and sunshade as well as nonwoven fabric were comparatively investigated in 2016 and 2017. Furthermore, the other three types of chill-proof measures including cold-proof cloth, anti-freezing chemicals and plastic steel frame greenhouse'were added to the experiment in 2017 and 2018. The efficient culster number per experimental plot was attained and the fruit number per cluster was obtained at full fruit period after chilling occurred, and the degree of fruit freezing injury was investigated at fruit ripening period. Besides, the fruits were collected at ripening period and quickly frozen in liquid nitrogen and thereafter preserved under-80 ℃ for the determination of fruit internal quality indexes, i.e., the contents of soluble solids (SS) , vitamin C (Vc) , titratable acid (TA) and total sugar (TS) . The contents of soluble solids were detected by the method of digital refractometer, and the levels of vitamin C were determined by the o-phenanthroline colorimetry method. Titratable acid contents were measured by the indicator titration method, and the contents of total sugar were detected by the method of anthrone colorimetry. Furthermore, the electronic balance and vernier caliper were applied for the detection of fruit external parameters, i.e., fruit weight and size separately.The fruit yield per 666.7 m2, however, was calculated by the formula: Fruit yield per 666.7 m2=fruit yield per plant×42 (plants) ×0.8. Afterwards, the number of effective cluster, fruit weight and size, fruit number per cluster, content of vitamin C and sugar acid ratio as well as solid acid ratio were compared directly by the one-way analysis of variance (ANOVA) (p < 0.05) (Mean ± SD) , while the fruit-setting ratio and the contents of soluble solids and total sugar were analyzed by ANOVA after arcsine formula to obtain normal distribution data.【Results】The results indicated that the fruit-setting ratio, and the efficient cluster number per experimental plot, the fruit number per cluster, and the fruit yield per 666.7 m2 in arch bar skeleton with polyethylene film chill-proof measure was significantly higher than the others. Similarly, the highest input-output ratio was also obtained in arch bar skeleton with polyethylene film chill-proof measure. However, none of the significant difference was found in fruit shape indexes among different chill-proof measures. Comparing the average fruit weight per plant, it was illustrated that the anti-freezing chemicals could obviously enhance the average fruit weight. In addition, the higher contents of soluble solids and total sugar from arch bar skeleton with polyethylene film were obtained comparing with other chill-proof measures. Furthermore, the levels of vitamin C and sugar acid ratio with cold-proof cloth treatment were remarkably higher than the others. For the highest solid acid ratio, however, was from sunshade chill-proof measure. Additionally, correlation analysis indicated that the content of soluble solids was significantly positive with vitamin C (p < 0.05) , sugar and acid ratio (p < 0.05) , total sugar (p < 0.01) , solid and acid ratio (p < 0.01) , respectively.【Conclusion】By comparing with the control, each chill-proof measure all had an efficient influence on fruit. Generally, arch bar skeleton with polyethylene film showed a better effect on cool prevention.