| Satsuma mandarin is one of the main wide-skinned oranges in China,with a wide planting area.However,most of the cultivated varieties are mainly mid-mature,and the proportion of early maturity is too low,and the variety structure still needs to be further optimized.Therefore,it is necessary to analyze the rule of quality formation among different Satsuma mandarin varieties at fruit developmental stages.In this study,extraprecocious ‘Gongben’,early-maturing ‘Guoqing No.1’ and late-maturing ‘Weizhang’were used as materials to explore the quality differences of different varieties during fruit ripening in the same habitat.The mainly results are as follows:1.Comparison of Fruit external quality of different ripening varietiesThe color,fruit weight,horizontal and vertical diameter,fruit firmness and pericarp thickness were measured during fruit developmental stages.It was found that the growth rate of extra-precocious ‘Miyamoto’ reached its peak at 78 d after anthesis,and completed the rapid expansion stage earlier than late-maturing ‘Owari’,with a shorter growth period,about 160 d.the coloring process of extra-early-maturing varieties was significantly faster than that of late-maturing varieties.The extra-early-maturing variety‘Miyamoto’ began to change color at 146 d after flowering.Coloring 15 d and 30 d earlier than early-maturing ‘Guoqing No.1’ and late-maturing ‘Owari’.2.Analysis on Internal quality difference and Gene expression of different ripening cultivarsThrough the determination of sugar,organic acids and Vc content during fruit developmental stages,it was found that the sucrose content of early-maturing varieties was significantly higher versus that of extra-precocious and late-maturing variety.Citric acid is the primary organic acid accumulated during Satsuma mandarin fruit growth.Much lower level content of citric acid was detected in extra-precocious and early maturing varieties than late maturing varieties.However,extra-precocious ‘Miyamoto’showing a higher citric acid content than ‘Guoqing No.1’.The reduction rate of citric acid in ‘Miyamoto’ was faster than that of ‘Guoqing No.1’ before changing color(136 d to 146 d after anthesis).In addition,much greater Vc content was detected in the extraprecocious ‘Miyamoto’ than the other two mature kinds.2.Analysis of genes Expression related to Sugar and Acid Metabolism in fruits of different ripening cultivarsThe expression levels of genes related to sugar and acid metabolism were analyzed,The results showed that Cr SPSA1,Cr SPS1 and Cr SS3 were highly expressed in extraprecocious varieties,and the expression in most periods in ‘Miyamoto’ was significantly higher than that in early-maturing and late-ripening varieties.Cr SS1 and Cr SS4 in extraprecocious varieties declined with fruit development,and Cr SS6 was significantly inversely correlated with sucrose content,which may be involved in the reversible decomposition of sucrose.The high expression level of Cr ACO2,Cr GAD1,Cr GS2,Cr ACLα2 and protein vector Cr Cit1 at the early stage of fruit developmental stage,along with the low expression of proton pump Cr PH8 may be the reasons for the rapid degradation of citric acid in the extra-precocious variety.3.Analysis of ABA content and expression of related genesThe ABA content of ‘Miyamoto’ reached the peak at 117 d after anthesis,which was30 d and 60 d earlier than that of early-maturing and late-maturing varieties,Based on the analysis of genes related to ABA synthesis,degradation and signal transduction,it was found that the expression of ABA synthesis gene Cr NCED2 in extra-precocious varieties was significantly higher than that of late-ripening varieties.The transcription level of ABA degradation related gene Cr CYP707A3 in all stages of extra-precocious varieties was lower than that of late-maturing varieties.In addition,the expression of ABA signal transduction gene Cr PYL2 in ‘Miyamoto’ was significantly higher than that in latematuring ‘Owari’(78 d to 146 d).The results showed that one of the signs of early maturity of extra-precocious varieties is the early production of high-level ABA content... |
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