Analysis of photosynthetic characteristics and fruit quality of Shine Muscat grafted on 4 grape varieties

Abstract: 【Objective】Xinjiang is an important grape producing region in China, with unique natural conditions and huge industrial scale. In recent years, Shine Muscat has attracted the attention of many fruit farmers because of its rich rose fragrance, high sugar content, low acid and other characteristics, and is regarded as the first choice for vineyard upgrading. The rapid renewal of varieties can be realized through the top- grafting method. In this study, the photosynthetic characteristics and fruit quality of Shine Muscat grafted on Victoria, Kyoho, Black Monukka, and Crimson seedless were studied in order to screen out old varieties suitable for grafting with Shine Muscat in Shihezi region of Xinjiang.【Methods】In May 2021, four nine-year-old grape varieties (Victoria, Kyoho, Black Monukka, and Crimson Seedless) were grafted using the greenwood grafting method and were designated as SM/VI, SM/KY, SM/BM, and SM/CR, respectively. Fruit appearance quality including transverse and longitudinal diameter, berry mass, single cluster mass, fruit color were assessed at the fructescence on September 5th, 2023. Intrinsic qualities including soluble solid content, titrable acid content, vitamin C content, soluble sugar content and soluble protein content were also measured. In late August 2023, the photosynthetic parameters including net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), in-tercellular CO2 concentration (Ci), chlorophyll content, and chlorophyll fluorescence were measured. For data analysis, single- factor analysis of variance was performed on the obtained experimental data. Correlation analysis was used to explore the relevance between indicators, and principal component analysis was used for comprehensive evaluation of the 4 stock- scion combinations.【Results】The results showed that the fruit quality of Shine Muscat was affected by the four rootstocks. Shine Muscat on Crimson Seedless had lower titratable acid and soluble protein contents and exhibited higher levels of soluble solids, soluble sugars, vitamin C, and solid to acid ratio. It had a single cluster mass of 919.19 g, with soluble solids reaching 21.63% and a solid to acid ratio of 62.08. The contents of chlorophyll a (Chl a), chlorophyll b (Chl b) and total chlorophyll (Chl a+b), net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), water use efficiency (WUE), and the maximum photochemical quantum yield of PSII (Fv/Fm) were highest in plants of SM/CR. The initial fluorescence (F0) and the maximum fluorescence yield (Fm) were highest in SM/BM. The correlation analysis showed that the berry mass had a highly significant positive correlation with indicators affecting photosynthetic rate. Total chlorophyll content had a significant positive correlation with photosynthetic characteristics and soluble proteins, and a highly significant positive correlation with chlorophyll b, soluble sugars, and intercellular carbon dioxide concentration. The initial fluorescence had a significant negative correlation with berry mass, L*, solid to acid ratio, net photosynthetic rate, intercellular carbon dioxide concentration, and the maximum light energy conversion efficiency of PSⅡ, and a highly significant negative correlation with single cluster mass and vitamin C content. The maximum light energy conversion efficiency of PSII had a highly significant positive correlation with solid to acid ratio, L*, a*, and h° values. The composite score was calculated based on the principal component comprehensive model, and according to the composite score, the performance of the four stock-scion combinations were in the order of SM/ CR>SM/ KY>SM/ VI>SM/ BM.【Conclusion】The results show that compared with Shine Muscat on the other three grape varieties, Shine Muscat grafted on Crimson seedless had higher contents of soluble sugars, soluble solids and sugar to acid ratio, with higher chlorophyll contents, stronger photosynthesis, and superior fruit quality. Overall, Crimson seedless is the most suitable rootstock among the four grape varieties for Shine Muscat.