Abstract: 【Objective】 The Queen Nina grape is famous nationwide for its excellent appearance and taste. However, its productivity and quality are largely limited by the climate factors such as high temperature, humidity, and insufficient light during the veraison stage, leading to poor fruit coloring and reduced sugar accumulation and reduced commercialization. Traditional techniques to improve grape berries coloration include trunk ring stripping, leaf removal, and fruit thinning, which are often labor-intensive and technically demanding for producers. In this study, we compared the advantages and disadvantages of spraying different plant growth regulators, amino acid fertilizers, and laying reflective film, and spraying water on the surface of the fruit as a control, with a view to selecting simple and easy cultivation practices to promote coloration and quality of Queen Nina berries. 【Methods】 Using Queen Nina, produced in facilities in a southern China production area (Wenzhou, Zhejiang) as the subject of the study, before turning color (E-L 34), fruit surface sprayed with trans-abscisic acid (T1, dilute 200×), Guodele (T2, dilute 1000×) , methyl jasmonate (T3, 50 mg·L-1) , Tianrunduocai (T4, dilute 1000×) , Jinchunqiu (T5, dilute 2000×), ethrel (T6, dilute 600×), Aiduoshou (T7, dilute 4000×), Aiguolong (T8, dilute 800×), laid reflective film (T9), and sprayed clean water as a control (CK). The first fruit sample was taken before treatment and thereafter at 10 d intervals for four consecutive times, recorded as DS0, DS1, DS2, DS3 and DS4, respectively. During fruit ripening, we measured the coloration level of the cluster, colour index for red grapes (CIRG), fruit morphogenesis, fruit hardness. The expression levels of the genes related to the synthesis of anthocyanin (VvCHS, VvUFGT, VvDFR and VvMYB90) in the skin, as well as the changes of the traits of the flesh such as the content of total soluble solids (TSS), soluble sugars and organic acids were analyzed. Meanwhile, the content of volatile organic compounds (VOCs) in the ripening berriess were also measured. 【Results】 Our findings revealed that, apart from T7 and T8, which contain sodium nitrophenol and amino acid fertilizers as active ingredients, all the other treatments were able to significantly enhanced fruit coloration and increased the expression of VvCHS, VvUFGT, VvDFR and VvMYB90 in the skin. Among them, T1 exhibited the most effective improvement in fruit coloration. At DS3, the coloration level of the cluster was 4.85 and the CIRG was 5.52 (meeting the criteria for deep red colour), with a content of 0.29 mg·g-1 of the total anthocyanin, but T1 was not able to effectively increase the content of soluble sugars and VOCs in the pulp. T3 not only improved fruit coloration and promoted the expression of related genes, but also drastically increased TSS, soluble sugars, VOCs, of which the content of the total anthocyanin in the skin and the content of soluble sugars and VOCs in the flesh at DS4 were 0.28, 180.40, and 30.28 μg·g-1, respectively. While both T1 and T3 had little effect on fruit longitudinal and transverse diameters, and reduced fruit firmness at fruit ripening, which was significantly lower than that of CK at DS4, being only 1.08 and 1.02 kg·cm-2, respectively. Whereas the T5 and T9 were very different, with significant effects on increasing fruit longitudinal and transverse diameters, and firmness. At DS4, the single grain weights of T5 and T9 were 14.77 and 14.99 g, respectively, which were 14.23% and 15.93% higher than that of CK, and the transverse diameters were 28.52 and 28.73 mm, respectively, which were 3.56% and 4.32% higher than that of CK. At DS4, the total organic acid content in the flesh of T4 treatment was relatively less only 2.79 mg·g-1, and there was no significant difference between the other treatments and CK, with the content ranging from 3.40 to 4.53 mg·g-1. In addition, T1, T2 and T4 were able to significantly increase the content of trans-2-hexenol, which was the most abundant terpene in the pulp of Queen Nina. Finally, a comprehensive evaluation based on subordinate function values analysis suggests that T3 was the most effective treatment overall. 【Conclusion】 50 mg·L-1 methyl jasmonate was selected as the best treatment method in this study to improve the color and quality of Queen Nina grape fruit. It not only promoted the expression of anthocyanin-related genes, effectively improved fruit color, but also increased TSS, soluble sugars, VOCs in the flesh.
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