不同果实发育期干旱胁迫对温州蜜柑果实品质形成的影响

Effect of drought stress at different development stages on fruit quality formation in Satsuma Mandarin

【目的】研究不同时期干旱胁迫对果实品质的影响,为提升果实品质及节水灌溉提供理论依据。【方法】以‘山下红’温州蜜柑(Citrus unshiu Marc.)为材料,分析了果实发育过程中细胞分裂期、果实膨大期及较长时期连续干旱后果实外在和内在品质的变化。【结果】与对照相比,不同果实发育阶段干旱胁迫后果实体积均呈下降趋势,细胞分裂期、果实膨大期、连续干旱期果实体积分别下降22.5%、49.6%、65.7%。对各处理成熟果实分析显示,连续干旱期处理总酸较对照升高86%,总糖升高6.5%,细胞分裂期干旱总酸较对照升高37.3%,总糖下降6%,果实膨大期干旱总酸较对照升高31.8%,总糖升高26.1%。发育过程中果实分析显示,细胞分裂期、果实膨大期和连续干旱严重阻碍了果实中柠檬酸降解,使果实中柠檬酸含量显著升高。【结论】综合不同果实发育阶段干旱胁迫后果实外在与内在品质的响应特点,不同时期干旱胁迫均导致温州蜜柑果实柠檬酸含量升高,细胞分裂期干旱导致果实品质发生高酸低糖的不可逆劣变,果实膨大期干旱对果实体积、糖和酸含量均有巨大影响。

【Objective】Moderate drought is an important means to regulate fruit quality.Citrus grows in southern China,where abundant rainfall happens during cell division but less rain during fruit enlargement,which is sensitive to drought.The impact of drought on fruit quality during different periods remains unclear.In this regard,the effect of drought on fruit quality at different fruit development stages was examined in order to provide strategy for improving citrus fruit quality with water-saving irrigation.【Methods】The experiments were carried out in National Centre for Citrus Improvement,Changsha,China.Five-year-old Satsuma Mandarin(Citrus unshiu Marc.‘Yamasitaka’)trees grafted on trifoliate orange[Poncirus trifoliate(L.)Raf.]were transplanted into plastic pots with a volume of 27 L.The cultivation medium was Vsawdust:Vriver sand:Vpeat=2:1:0.5.A TDR300 portable soil moisture analyzer(Spectrum Technologies,USA)was used to measure water content in the substrate.Water content below40%(relative to maximum water holding capacity of the substrate)was considered as drought stress.Drought treatment was applied at fruit cell division stage(June-July),fruit enlargement stage(AugustSeptember)and throughout the whole fruit development stage(June-September)in this study.Meanwhile,normal irrigation(approximate 70%of the maximum water holding capacity in the substrate)was treated as the control.The control group and each of the treatment groups had 10 trees.Nine fruit were collected at each time of sample collection,and the appearance indexes were determined immediately after fruit collection.The fruit were divided into two parts,half of which were stored in the refrigerator at-20℃,while the other half was quickly peeled and frozen in liquid nitrogen and stored at-80℃.High performance liquid chromatography(HPLC)and direct measurement were performed to analyze the changes in external and internal quality indexes during fruit development.【Results】The results showed that fruit volume decreased after drought stress during different fruit development periods.Fruits under persistent drought showed a smallest fruit size,which was 65.7%lower than that of control.Besides,fruit size under drought at fruit enlargement stage and cell division stage was 49.6%and22.5%smaller than that of the control,respectively.The results indicated that drought during fruit enlargement had a greater impact on fruit development,and was the key period affecting fruit size and yield.Analysis of the mature fruit showed that total acid and sugar increased by 86%and 6.5%under continuous drought stress,respectively.Total acid increased by 37.3%and total sugar decreased by 6%in the group with drought applied during cell division compared with the control.Meanwhile,total acid and total sugar increased by 31.8%and 26.1%in drought treatment applied during fruit enlargement,respectively.Furthermore,restoring irrigation after drought stress during cell division exhibited no obvious effect on sugar decrease and acid increase,suggesting that drought during cell division had irreversible negative effects on fruit quality.The sugar-acid ratio in mature fruit in drought stress at different fruit development periods was the highest in the control and in the drought treatment during fruit enlargement,followed by the group with drought during cell division,and the continuous drought group was the lowest,indicating that drought during fruit enlargement had a great effect on sugar and acid metabolism and thus on fruit quality formation.In addition,all drought treatments resulted in increased in organic acids in fruit.Citric acid is the major acid,accounting for over 75%of total acids.The degradation of citric acid in fruit under drought treatments was seriously hindered,leading to increased organic acid content in fruit.【Conclusion】Drought stress at different periods of fruit development may intensify citric acid synthesis and suppress its degradation.Drought during cell division causes an irreversible deterioration of fruit quality with high acid and low sugar contents.Drought during fruit enlargement has a great impact on fruit volume as well as sugar and acid contents.