Research On Supporting High-quality Cultivation Technology Of ‘Qingji’

‘Qingji’ is a high-quality,mature mandarin orange variety introduced from Japan,with the characteristics of high sugar content,low acidity,fine and tender flesh,clear and sweet taste,and easy peeling.Currently,it is distributed in production areas such as Jiangxi and Zhejiang province.Similar to most miscellaneous citrus varieties,‘Qingji’ is sensitive to temperature.Based on the preliminary production area investigation,‘Qingji’ exhibited a significant change in fruit quality with the change of climatic conditions in the Fuzhou production area,especially during the mature period,where continuous low-temperature and rainy weather further exacerbated the differences in fruit quality.This present research aimed to address issues such as uneven quality and optimal harvest time of ‘Qingji’ in production.By combining cultivation measures such as fruit bagging,covered with reflective film treatment,fertilization,and irrigation,this study conducted research on‘Qingji’ grown in open field and rain shelter,technical support and practical basis for the supporting production program of high quality ‘Qingji’ fruits.The specific conclusions are as follows:1.Comparison and analysis of fruit quality at different harvesting periodsCombined with the comprehensive quality index of the fruit,it was determined that November 25 and December 5 were the most suitable fresh harvesting periods for ‘Qingji’fruit.In the Fuzhou(Jiangxi Province)production area,the turning color period of ‘Qingji’fruit grown in open field is around 190 days after flowering(200 days after full bloom).Fruit harvested on November 25 th had the highest fruit peel brightness,closest to orange color,highest edible rate,and juice yield.Fruit harvested on November 25 th and December5 th had significantly higher TSS content than those harvested on November 15 th and December 15 th,with average values of 15.51% and 15.53%,respectively.The TSS and VC contents of ‘Qingji’ fruit showed a trend of increasing first and then decreasing from November 15 th to December 15 th,with the fruit harvested on December 5th having the highest VC content,with an average value of 46.19 mg/100 g,while the TA content showed a gradually decreasing trend.2.Effects of different fertilization and reflective film coverage treatments on fruit quality(1)In the 2021 experiment,the TSS content of fruit from the F1 treatment group[basal fertilizer(containing 10 kg organic fertilizer +1 kg of compound fertilizer + 0.3 kg of Calcium and magnesium phosphate fertilizer + 0.5 kg of quicklime)+ 1 kg of fruitstrengthening fertilizer + reflective film coverage)] and the F2 treatment group [basal fertilizer(containing 20 kg organic fertilizer + 1 kg of compound fertilizer + 0.3 kg of calcium and magnesium phosphate fertilizer + 0.5 kg of quicklime)+ 1 kg of fruitstrengthening fertilizer] reached 11.20% and 11.22%,respectively.The TSS content of F2 was significantly increased by about 10.55% compared to CK [basal fertilizer(containing10 kg organic fertilizer + 1 kg of compound fertilizer + 0.3 kg of Calcium and magnesium phosphate fertilizer + 0.5 kg of quicklime)+ 1 kg of fruit-strengthening fertilizer].The fruit from F1 and F2 had significantly higher levels of fructose and sucrose than CK,while the total acidity and citric acid content were lower than CK,and the fruit peel color of F1 and F2 was closer to orange than that of CK.(2)In the 2022 experiment,F1 had the highest VC content,with an average of 42.98mg/100 g.The fructose content,glucose content,total sugar content,total acid content,and citric acid content of F2 were significantly higher than the control CK.The increase in fructose,glucose,and total sugar in F2 compared to CK was 13.73%,19.84%,and 8.13%,respectively.F2’s malic acid content was significantly lower than CK.The TSS content of fertilization and reflective film covering treatments F3 [basal fertilizer(containing 20 kg organic fertilizer + 1 kg of compound fertilizer + 0.3 kg of calcium and magnesium phosphate fertilizer + 0.5 kg of quicklime)+ 1 kg of fruit-streng-thening fertilizer +reflective film coverage)] and F5 [basal fertilizer(containing 25 kg organic fertilizer +1 kg of compound fertilizer + 0.3 kg of calcium and magnesium phosphate fertilizer + 0.5 kg of quicklime)+ 1 kg of fruit-strengthening fertilizer + reflective film coverage)] reached14.49% and 15.39%,respectively,and the TSS content of F3 and F5 was significantly higher than CK.The fruit skin color of F3 and F5 was significantly closer to orange compared to CK.F3 had significantly higher fructose content,sucrose content,and total sugar content than CK.The average fructose content of F5-treated fruit reached 69.62 mg/g,the highest among all treatment combinations,and both F3 and F5 treatments significantly improved the appearance and intrinsic quality of ‘Qingji’ fruits.3.Effects of different water irrigation treatments on fruit qualityThe two-year repeated experiment was conducted in a rain-sheltered environment,the irrigation treatment(I1)mainly affected the fruit TSS content and solid acid ratio,and had no significant effect on other fruit quality indicators.It mainly affected the TSS content and solid acid ratio of the fruit.In 2021,the average TSS content of I1 was 10.44%,significantly lower than the average TSS content of Water control treatment(CK)at 11.12%.In the 2022 experiment,the TSS content of fruit harvested from I1 treatment at all four harvesting periods was lower than that of CK,and the average TSS content of fruit harvested on December 15 th in I1 treatment was 14.03%,significantly lower than the average TSS content of CK at 15.37%.The increase in moisture decreased the TSS content of mature‘Qingji’ fruit,and the decreasing trend of TSS content was faster in the late ripening stage of fruit in I1 treatment than in CK.4.Effects of different bagging treatments on fruit quality(1)In the 2021 experiment,the average TSS content of fruit in T1 treatment(doublelayer paper bagging)was 11.62%,significantly higher than the average TSS content of CK(Fruits were not bagged),with an increase of 9.11%.The glucose and fructose content of T1 were significantly lower than that of CK,but the sucrose content was higher than CK.There was no significant difference in the total soluble sugar content between T1 and CK.The citric acid content and total acid content of T1 were lower than CK,but the difference was not statistically significant.(2)In the 2022 experiment,a T2 treatment(non-woven fabric bagging)was added.T1 treatment had the highest TSS content,with an average value of 15.07%.T1 and T2 had significantly higher TSS content than CK,with an increase of 28.69% and 26.99%,respectively.The T1’s solid acid ratio was significantly higher than CK,with an average value of 32.00.Both T1 and T2 had significantly higher VC content than CK’s 35.22mg/100 g.The edible rate and juice yield of T1 and T2 treatments were significantly lower than CK.T1 and T2 had significantly higher soluble sugar total content,fructose content,sucrose content,glucose content,organic acid total content,and citric acid content than CK,but there was no significant difference in malic acid content.The fruit skin freeze injury rates of T1,T2,and CK were 16.67%,83.33%,and 93.33%,respectively.The fruit skin freeze injury rate of T1 was significantly lower than that of CK and T2.