Fruit Quality Change In Delayed Harvested Citrus Under Protected Cultivation

The northwestern Hubei is north area of citriculture in china,and Danjiangkou ismain growing areas in Hubei Province. As a result of less accumulated temperature andlong frost season, harvesting time is short,fruit quality is low.Trying to improve thequality of fruits,elongate the harvesting time,the study was carried out on delayed harvestcultivation in plastic house by using Kamei satsuma mandarin(Citrus unshiu Marc),Newhall navel orange (Citrus sinensis L.) and Okitsu wase(Citrus reticulata Blanco) asmaterial.There are two different irrigation system in plastic house and open-field forcontrast, studied on effect of different environment in plastic house and in the field onfruit development and fruit quality.The main results were as follows:1.Effect of protected cultivation on environmentAccumulated temperature of protected fields was significantly increased,the≥10℃accumulated temperature was 1867℃in protected field while 1230℃in open field fromSep 15 to Jan 15.The daily mean temperature of protected field was 4.3℃higher than thatof the open field averagely, the difference was significantly after November, maxdifference was 11.5℃.The daily max temperature of protected field was 6℃higher thanthat of the open field averagely, the difference was significantly in December, averagedifference was above 10℃,max difference was 18℃.The daily minimum temperature ofprotected field was higher than that of the open field averagely.The protected cultivation changed air relative moisture,the relative moisture ofprotected field higher than that of the open field,the average air relative moisture was75.7% in protected field while 67.1% in the open field.The soil relative moisture wascontrolled better in protected field,the difference between protected and open field of soilrelative moisture in October was no significant, and then moisture of the open fieldincreased,with higher peak appearing in end of December;the soil moisture of protectedfield under water controlling was decreased after October, and then maintained 55%;thesoil moisture of contrast in protected field keep about 80%.The average soil moisture was77.7% in the open field,64.7% in protected field under water controlling,and in 75.9% inin protected field of contrast.2.Effect of protected cultivation on ripening stageThe color break of pericarp was about in 190d after full bloom namely end ofOctober, L value of protected cultivation higher than that of the open field in late 2005,thismeans pericarp brightness of protected delayed cultivation higher than that of the openfield.The increasing of a/b ratio in protected field under water-regulating more rapidlyfrom 170d to 190d after full bloom in 2006,this means colouration of protected fieldunder water-regulating earlier, the color break of pericarp delayed in protected field,butpericarp brightness of protected field under water controlling earlier higher than that ofthe open field and the contrast.3.Effect of protected cultivation on fruit quality puffiness rate:The puffiness rate of delayed harvest in 2005 increased both inprotected field and in the open field,at last increased to 20%,and there were no significantdifference in protected field and in the open field; however, the puffiness rate of protectedfield under water controlling was significant lower than that of the open field and thecontrast before December in 2006, maintained about 5%,but significant increased inJanuary of 2007.Total soluble solid(TSS) and titratable acidity(TA): In 2005,TSS of fruit in protectedfield and the open field increased from September to November, after November, freezeinjury and abscission of fruits appeared in the open field then fruits lose commercialvalue,and TSS of fruit in protected field decreased.In 2006,TSS of fruit increased beforethe middle November, then maintained stable,as a whole,TSS of protected field underwater controlling higher than that of the open field.TA of fruit presented a declinetendency both in protected field and in the open field,TA of Newhall navel orange wassignificantly higher than that of Kamei satsuma mandarin in 2005,and TA of protectedfield under water controlling higher than that of open field in delayed harvest of 2006.Dietary fiber(DF):DF of pulp presented a slow decline tendency during ripeness,thenmaintained stable after 190d after full bloom.The changes tendency of DF in protecetedfield and the open field showed identity, only difference in diverse variety in 2005.Before210d after full bloom in 2006,DF of protected field under water controlling wasmaximum,the next was the open field,then was the protected field of contrast.Sugars and acids contents:As a whole, sucrose content increased, glucose contentmaintained stable,and fructose content slowly decreased along with maturity. Glucose andfructose contents of Kamei satsuma mandarin in protected field higher than that of in theopen field in delayed harvest in 2005.In 2006, sucrose content of protected field underwater controlling significantly increased in early December and higher than that of theopen field and protected field of contrast,while the fructose and glucose contents changeswere reverse;and then the fructose and glucose contents of protected field under watercontrolling were higher than that of the open field and protected field of contrast after lastDecember.Citric acid content of protected field under water controlling presented twodecline tendency but whereafter increased, citric acid content of protected field of contrastdeclined at early and increased at last,citric acid contect of the open field slowlydeclined.This means the conversion of citric acid maybe effect by water.In 2005,total sugar content of Kamei satsuma mandarin in protected fieldsignificantly higher than that of in the open field,total sugar content of Newhall navelorange lower than that of in the open field;total acid content of Kamei satsuma mandarinin protected field lower than that of in the open field,while changes of Newhall navelorange was reverse.In 2006,total sugar content of protected field significantly higher thanthat of the open field,changes of total sugar and total acid in the open field were nosignificant,total sugar content in protected field increased while total acid decreased;glucose and fructose contents in protected field under water controlling significantly increased after December, then total sugar content significantly increased too.This meansthat accumulation and transform of sugar and acid still proceeded in delayed harvest,theratio of sugar to acid significantly higher than that of normal harvest.