The 8th International Horticulture Research Conference July 20 - 22, 2021, Nanjing, China & Zoom Webinar Difference in fruit quality and citric acid metabolism between a early-ripening mutant of navel orange (Citrus sinensis) and its parental ‘Newhall’ during cold storage Xuezhen Yang1, Xiu Chen1, Zhenyu Luo1, Qiang Wang1, Miaolian Xiang1, Ming Chen1* and Jinyin Chen1,2* 1Jiangxi Key Laboratory of Postharvest Technology and Nondestructive Testing of Fruits & Vegetables, Jiangxi Agricultural University, Nanchang 330045, China 2Pingxiang University, Pingxiang 337055, China *Corresponding author. Email: [email protected] or [email protected] Background The content of organic acids directly affects fruit flavor, the change of organic acid content is directly related to the citrus fruit quality during postharvest storage, and different citrus varieties have different citric acid homeostasis patterns[1-3]. A natural bud mutant of ‘Newhall’ (Citrus sinensis) navel orange, discovered in 2019, ripen half a month earlier than its parental, its TA content (0.75%) was significantly lower than that of Newhall (1.03%). Methods Newhall and its early-ripening mutant fruits were used in this study. The fruits of the two varieties were harvested at maturity and stored under refrigeration (6±0.5 ℃ , 95±2% RH) for 80 days. The two cultivars postharvest quality changes and citric acid metabolism-related gene transcription levels were analyzed in order to found the reasons for the low acidity of the early-maturing mutant fruits. Results Mutant fruits had higher Citrus Color Index (CCI), Total soluble solids (TSS), TSS/TA and lower h value, L value and Titratable acidity (TA) (Fig. 1 and Fig. 2). During storage, the contents of TSS and soluble sugar content (SSC) of the two varieties fruits increased first and then decreased, the ratio of TSS/TA gradually increased, however, the change trend of TA content was opposite, the mutant fruits first increased then decreased, while the Newhall fruits first decreased then increased. We analyzed the changes of the organic acids composition of two cultivars by HPLC, found that citric acid, quinic acid and tartaric acid were the main organic acids of the two varieties. The citric acid content of the mutant fruit was significantly lower than Newhall during the whole storage, but the content of quinic acid was significantly higher than that of Newhall at the early stage of storage (0-40d) (Fig. 3). Gene expression results showed that the citric acid synthesis-related genes (including PEPC1/2/4 and CS1) and citric acid degradation-related genes (including Aco1/2/3, IHD1/2/3, GAD4/5, ACLα1/α2/β, PEPCK1/2 and FBPase1)of the mutant fruits were lower than those of Newhall, and the expression level of PEPC2 had the largest difference (Fig. 4). Conclusion The mutant fruit has better flavor quality during postharvest storage. The reason for the low acidity of the mutant fruit may be related to the lower expression of PEPC2 The 8th International Horticulture Research Conference July 20 - 22, 2021, Nanjing, China & Zoom Webinar gene involved in the citric acid synthesis pathway. Funding This work was financially supported by the Innovation Fund Designated for Graduate Students of Jiangxi Province (YC2020-B085) and Natural Science Foundation of Jiangxi Province (20181BAB204013). Fig.1 (A) The fruits of Newhall and its early-maturing mutant were harvested at the same time. (B) The values of Citrus Color Index (CCI) and the of a, b, c, h and L of the two varieties during cold storage. The 8th International Horticulture Research Conference July 20 - 22, 2021, Nanjing, China & Zoom Webinar Fig.2 Changes of Titratable acidity (TA), Total soluble solids (TSS), soluble sugar content (SSC), TSS/TA, weight loss rate and respiration intensity of Newhall and its early-maturing mutant during cold storage. The 8th International Horticulture Research Conference July 20 - 22, 2021, Nanjing, China & Zoom Webinar Fig.3 Changes in the contents of organic acids of Newhall and its early-maturing mutant during cold storage. The 8th International Horticulture Research Conference July 20 - 22, 2021, Nanjing, China & Zoom Webinar Fig.4 The genes expression of citric acid metabolism of Newhall and its mutant during cold storage. (A) citric acid biosynthesis pathway, (B) GABA shunt in citric acid degradation pathway, (C) ACL shunt in citric acid degradation pathway. References 1. Wei, Q. J., Ma, Q. L., Zhou, G. F., Liu, X., Ma, Z. Z., & Gu, Q. Q. (2021). Identification of genes associated with soluble sugar and organic acid accumulation in ‘Huapi’ kumquat (Fortunella crassifolia Swingle) via transcriptome analysis. Journal of the Science of Food and The 8th International Horticulture Research Conference July 20 - 22, 2021, Nanjing, China & Zoom Webinar Agriculture, 101(10), 4321–4331. https://doi.org/10.1002/jsfa.11072 2. Liu, Y. Z., Liu, Q., Xiong, J. J., & Deng, X. X. (2007). Difference of a citrus late-ripening mutant (Citrus sinensis) from its parental line in sugar and acid metabolism at the fruit ripening stage. Science in China, Series C: Life Sciences, 50(4), 511–517. https://doi.org/10.1007/s11427-007-0063-8 3. Sheng, L., Shen, D., Yang, W., Zhang, M., Zeng, Y., Xu, J., Deng, X., & Cheng, Y. (2017). GABA Pathway Rate-Limit Citrate Degradation in Postharvest Citrus Fruit Evidence from HB Pumelo (Citrus grandis) × Fairchild (Citrus reticulata) Hybrid Population. In Journal of Agricultural and Food Chemistry (Vol. 65, Issue 8). https://doi.org/10.1021/acs.jafc.6b05237.