Comprehensive evaluation of fruit quality of 12 red table grape cultivars cultivated in Yangling area based on principal component and cluster analyses

Abstract：【Objective】China is the largest producer of table grape in the world. Yangling is located in the hinterland of Guanzhong plain in Shaanxi, which is an important table grape production region in northwest China. Table grape cultivation and production in Yangling area has been playing an important role in increasing farmers' income and improving ecological environment. However, local table grape industry is based on a single red cultivar resulting in concentrated mature period, which prevents sustainable development of table grape in this area. Therefore, it is required to select high- quality red table grape cultivars to broaden cultivar structure. The objective of this study was to comprehensively evaluate fruit quality of 12 red table grape cultivars available in Yangling using statistical methods, such as descriptive statistics, correlation analysis, principal component analysis and cluster analysis, in order to provide reference for selecting high-quality table grape cultivars.【Methods】The experimental materials were taken from the Grape Seedling Breeding Base of Xinji village in Yangling. Single fruit weight (SFW), fruit shape index (FSI), L*, a*, b*, hardness, fractur ability, adhesiveness, springiness, cohesive-ness, gumminess, chewiness, resilience, soluble solids content (SSC), reducing sugar content (RSC), titratable acid content (TAC), sugar-acid ratio (RSC/TAC), edible rate (ER), moisture content (MC), juice yield (JY), protein content (PC) and VC content of fruit were measured. SPSS and Excel software were used for data analysis. Before principal component analysis, the original data were transformed with Zscore normalization method. According to the variance contribution rate ≥ 85%, the number of principal components was determined, and based on the component scoring coefficient matrix, the score of each cultivar on the corresponding principal component was obtained. The relative contribution rate of variance of each principal component was taken as the weight, and the comprehensive score of each cultivar was summed to obtain the principal components score and the corresponding weight value. The 12 red table grape cultivars were ranked according to the comprehensive scores. Furthermore, the characters of fruit were further analyzed using systematic cluster analysis, and sensory evaluation of each cultivar was conducted.【Results】The result showed the fruit quality traits of the 12 cultivars varied significantly. Among the traits, relatively small coefficients of variation (CV) was observed in the ER (1.22%), MC (2.99%) and JY (5.23%), and relatively large CV observed in the b* (377.38%) and adhesiveness (105.69%). There was a simple correlation between some quality traits. In principal component analysis, five principal components were extracted with a total cumulative contribution rate of 88.55% , which reflected most of the quality characteristics of red table grape fruits. The contribution rate of the first principle component (PC1), which included hardness, fractur ability, gumminess, chewiness, SSC, RSC, RSC/TAC, VC, and MC, was 30.46%. The contribution rate of the second principle component (PC2) consisting of L*, a*, b*, and TAC was 19.41%. The third principal component (PC3) included springiness, cohesiveness, resilience and JY, with a variance contribution rate of 15.68%. The contribution rate of the forth principle component (PC4) including FSI, b* and PC was 11.63%. The fifth (PC5) with a contribution rate of 11.39% included SFW, ER and adhesiveness. The former five principal component scores of each cultivar were analyzed, which showed the distribution of fruit quality. The cultivars with top four synthetical scores of PC1 were‘Seedless Grape’‘Summer Black’ ‘Miguang’and ‘Kyoho’. The top four cultivars based on PC2 score were‘Seedless Grape’‘Yatomi Rosa’‘Muscat Grape’and‘Kyoho’. The top four cultivars based on PC3 score were‘Miguang’‘Zana’‘Summer Black’and‘Manicure Finger’. The top four cultivars based on PC4 score were ‘Manicure Finger’ ‘Zao Juxuan’ ‘Seedless Grape’ and ‘Moldova’. And the top four cultivars based on PC5 score were ‘Summer Black’‘Kyoho’ ‘Hutai-8’and‘Manicure Finger’. According to principal component analysis, the comprehensive score of each cultivar was gotten. The result of cluster analysis indicated that the 12 cultivars could be divided into four groups in the cluster analysis at a Eudlidean distance of 10. The results of cluster analysis can be ranked by comprehensive scores. The comprehensive quality of ‘Seedless Grape’ ‘Manicure Finger’ ‘Summer Black’ and ‘Miguang’ was the best in this study, while the quality performance of ‘Jingya’ ‘Zaojuxuan’ and ‘Moldova’ ranked the lowest. Sensory evaluation results were consistent with the comprehensive evaluation results.【Conclusion】Principal component combined with cluster analysis used to evaluate fruit quality is reliable. However, the value of single index could not completely reflect the comprehensive quality of cultivars. For example, fruit color, fruit rust and other external indicators were also important factors affecting the quality of table grape. Further evaluation of other agronomic characters on the top of quality evaluation is necessary to screen excellent cultivars adapted to local regions.