Study on the accumulation of anthocyanins in the peel during fruit development with the new grape bud sport cultivar Nantaihutezao

Abstract:【Objective】Grape color is an important basis for consumers to choose berries, and thus directly related to economic benefits. Anthocyanins are the basis for the color of grapes, and their composition and content affect the color change. In southern areas, the temperature difference between day and night is small, so the difficulty in coloring of grapes has become a bottleneck in the development of the grape industry. Therefore, it is urgent to improve color through genetic breeding. Bud sport is a somatic mutation, commonly used as an essential method for fruit color breeding, and lots of cultivars have been bred in this way. Nantaihutezao is a novel bud sport cultivar from Summer Black bred by Zhejiang University, with earlier veraison, advanced maturity and deep color setting, therefore having great potential for promotion and research. In order to understand the influence of bud sport on the anthocyanin composition and accumulation in grape berry peel, several analyses were carried out using Nantaihutezao and its parent Summer Black as materials.【Methods】In this study, 3-year-old Nantaihutezao and Summer Black vines grown in the Huajiachi Experimental Education Base of Zhejiang University were used, the rootstock was 5BB, and they were cultivated under the condition of rain shelter and root restriction. Grapevines were planted in south- north rows at a planting space of 2.2 m × 8 m with short cane pruning system and routine watering and fertilizing strategy. The two cultivars had basically the same bud break and flowering periods. Samples were collected every 7 days from veraison (May 29, 2019, 24 days after flowering) to berry ripening (the pulp soluble solids content reached 17 %, considered to reach the maturity standard). Three biological repeats were designed for each cultivar. The longitudinal and cross diameter were measured with the vernier caliper, and the total soluble solid content (TSS) was measured with a refractometer PR101-a (Atago). The anthocyanin components in the skin of mature berry were identified by ultra performance liquid chromatography tandem triple quadrupole time-of-flight mass spectrometry (UPLC- Triple- TOF 5600+ ), using the fingerprint library of grape and wine anthocyanins established by China Agricultural University as a reference, and the anthocyanin components were determined according to the retention time and mass spectrum information. The anthocyanin content during fruit development was determined by high performance liquid chromatography (HPLC). The relative content of anthocyanin components was calculated by using cyanidin-3-O-glucoside as a external standard quantification.【Results】During the development process, the changes in fruit size of two cultivars were basically the same, but the first expansion period of Nantaihutezao berry ended earlier and TSS reached 17 % 7 days earlier than Summer Black. Inflorescences of Nantaihutezao began to change color partially at 31 DAF, and the skin color became dark purple at 52 DAF, which was similar to that at the ripening stage (73 DAF). By comparison, the skin of Summer Black berry showed obvious color change until 45 DAF, and the coloration was slower in the early stage. It showed reddish from 45 to 66 DAF, and turned reddish-purple when it was close to maturity. A total of 15 anthocyanins, including peonidin (Pn), delphinidin (Dp), petunidin (Pt) and malvidin (Mv) derivatives, were detected in the ripe berry peels of Nantaihutezao and Summer Black. Among them, 11 anthocyanins were detected in both cultivars, however, peonidin-3, 5-O-diglucoside (Pn-DG) and malvidin-3-O- (6-O-coumaryl) -5-O-diglucoside (Mv-DG-Co) were only detected in Nantaihutezao, and malvidin-3,5-O -diglucoside (Mv-DG) and malvidin-3-O-(6-O-acetyl)-glucoside (Mv-G-Ac) were only detected in Summer Black. Malvidin derivatives were the main anthocyanins, and the content of monoglucoside was higher than that of diglucoside in both cultivars. The total anthocyanin content of Nantaihutezao was about 1.5 times more than Summer Black in the skin of ripening berry. The anthocyanin accumulation curve of two cultivars was quite different. Nantaihutezao berry skin began to accumulate anthocyanins 7 days earlier than Summer Black, and peonidin derivatives accumulated rapidly and largely from 31 to 38 d, while delphinidin derivatives (Dp, Pt, Mv) accumulated rapidly from 31 to 52 DAF, reaching a level equivalent to the mature period, which may contribute to its dark purple berry skin. By contrast, the rapid accumulation period of anthocyanins in Summer Black berry skin was found from 38 to 52 DAF, and the accumulation amount was significantly less than that of Nantaihutezao. Moreover, the appearance of peonidin-3,5-O-diglucoside (Pn-DG), delphinidin-3-O-(6-O-coumaryl)-5- O-diglucoside (Dp-DG-Co), malvidin-3-O- (6-O-acetyl) -glucoside (Mv-G-Ac), petunidin-3-O- (6-O-coumaryl) -5-O-diglucoside (Pt-DG-Co) and peonidin-3-O- (6-O-coumaryl) -5-O-diglucoside (Pn-DG-Co) was delayed for 7 d in Summer Black.【Conclusion】The composition and content of anthocyanins determined the color of grape. Compared with Summer Black, the anthocyanins in the skin of Nantaihutezao accumulated earlier, faster, and higher in contents, so it had the characteristics of early veraison, faster color change, and deep color setting. Bud sport promoted variation in the components and accumulation of anthocyanins in grape skins, which made the difference in the color change process and final color appearance between the new cultivar and its parent.