Different cultivation practices promote berry coloration and quality in Queen Nina grape

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 berry coloring, reduced sugar accumulation and reduced commercialization. Traditional techniques to improve grape berry coloration include trunk girdling, leaf removal, and cluster and berry thinning, which are often laborintensive and technically demanding for producers. In this study, we compared the advantages with disadvantages of spraying different plant growth regulators or amino acid fertilizers, and laying reflective film, with spraying water on the berry surface serving as a control, so as to select simple and easy cultivation practices to promote coloration and quality of Queen Nina berries.【Methods】With Queen Nina, produced in facilities in a southern China production area (Wenzhou, Zhejiang) as the sample, before turning color (E-L 34), the berry surface was sprayed with trans-abscisic acid (T1, dilute 200×), Guo-dele (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× ), the reflective film (T9) was laid on the ground, and clean water was sprayed as a control (CK). The first 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 berry ripening, we measured the coloration level of the cluster, colour index for red grapes (CIRG), berry morphogenesis and berry 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 contents of volatile organic compounds (VOCs) in the ripening berries were also measured.【Results】Our findings revealed that, apart from T7 and T8, which contained sodium nitrophenol and amino acid fertilizers as active ingredients, all the other treatments were able to significantly enhance berry coloration and increase the expression of VvCHS, VvUFGT, VvDFR and VvMYB90 in the skin. Among them, T1 exhibited the most effective improvement in berry 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 and VOCs, in 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. Both T1 and T3 had little effect on berry longitudinal and transverse diameters, and reduced berry 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 berry 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 contents 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 suggested that T3 was the most effective treatment overall.【Conclusion】50 mg·L-1 methyl jasmonate was selected as the best treatment in this study to improve the color and quality of Queen Nina grape berry. It not only promoted the expression of anthocyanin-related genes, so as to effectively improve fruit color, but also increased TSS, soluble sugars and VOCs in the flesh.