Comprehensive evaluation of fruit quality of new late-maturing mandarin cultivars

Astract:【Objective】The variety structure of citrus is unreasonable in China, as there is a shortage of late-maturing cultivars with good quality for fresh consumption. Therefore, breeding and selection of latematuring citrus cultivars are urgently demanded. A reasonable evaluation of fruit quality is important for citrus breeding and selection. The study aims to establish a comprehensive evaluation method to select new excellent late-maturing mandarin cultivars.【Methods】Seven external quality indices and six intrinsic quality indices were used to assess the fruit quality of‘Gold Nugget'‘Shasta Gold'‘Tahoe Gold'‘Tango'and‘Yosemite Gold', the new late-maturing mandarin cultivars introduced from America, and‘W. Murcott', one of the main local cultivars. We sampled fruits from Fengjie, Zhongxian, Kaizhou and Jiangjin, which are the main citrus producing regions in Chongqing municipality. Quality indices including single fruit mass, vertical diameter, horizontal diameter, fruit shape index, peel thickness, lightness (L) , green-red (a) values, blue-yellow (b) values, edible rate, number of seeds, total soluble solids (TSS) , titratable acidity (TA) , vitamins C and ratio of total soluble solids/titratable acidity (TSS/TA) , were measured and then analyzed by factor analysis and cluster analysis. Before factor analysis, the original data were transformed with Z-score normalization method. KMO test and Bartlett's test were used to verify the appropriateness of factor analysis. The principal component analysis method was used to extract the factors.The fruit quality scores of all samples were calculated by the comprehensive score model. By comparingthe scores of fruit quality between the five new cultivars introduced from America and the local cultivars in the same district, we selected the excellent late-maturing mandarin cultivars that will be potentially popularized in the four regions. The overall scores of fruit quality in the four regions were used to rank fruit quality of the six cultivars. Cluster analysis was used to intuitively classify all the samples according to their quality differences and to support the result of factor analysis.【Results】The coefficient of variation of fruit quality indices in the four regions were calculated, and showed that all of the fruit quality indices were basically consistent in different regions except the number of seeds and values of a/b, TSS, TA and TSS/TA.‘Gold Nugget'‘Shasta Gold'and‘Yosemite Gold'had larger fruit size and heavier fruit weight than the other three. Fruits of‘Tahoe Gold'and‘Yosemite Gold'had the deepest red color, and‘Gold Nugget'was the shallowest in redness.‘Gold Nugget'and‘Shasta Gold'were seedless.‘Tahoe Gold'‘Tango'and‘Yosemite Gold'were basically seedless, and‘W. Murcott'was the most seedy cultivar. Fruit quality of the six late-maturing mandarin cultivars was excellent, and‘Gold Nugget'was highest in TSS, ‘Shasta Gold'‘Tahoe Gold'and‘Yosemite Gold'were highest in vitamin C, ‘Tango'was excellent in TA. The result of KMO test and Bartlett's test showed that the data of fruit quality were suitable for factor analysis. Cumulative contribution rate of the first five factors, extracted by principal component analysis, reached 85.38%, which meant that the first five factors retained most of the original variable information. Therefore, the information of the first five factors was used for the next step analysis. The results of quality comprehensive score and ranking of cultivars calculated by the comprehensive score model, showed that the fruit quality scores of‘Gold Nugget'‘Shasta Gold'and‘Yosemite Gold'cultivated in Kaizhou region were better than those of‘W. Murcott', which demonstrate that‘Gold Nugget'‘Shasta Gold'and‘Yosemite Gold'are promising in Kaizhou. The fruit quality scores of the five introduced new late-maturing mandarin cultivars were better than those of‘W. Murcott'in Jiangjin, which demonstrate the five introduced cultivars are promising in Jiangjin. The fruit quality scores of‘Gold Nugget'‘Shasta Gold'‘Tango'and‘Yosemite Gold'were better than those of‘W. Murcott'in Fengjie, which demonstrates the four cultivars are promising in Fengjie. The result of cluster analysis showed that all the samples were clustered into three categories.‘Shasta Gold'‘Tahoe Gold'and‘Yosemite Gold'from the four regions were clustered into group Ⅰ, whose scores calculated by factor analysis were the second highest.‘Gold Nugget'from the four regions were clustered into group Ⅱ, whose scores were the highest.‘Tango'and‘W. Murcott'were clustered into group Ⅲ, whose scores were the lowest. The results of cluster analysis were basically consistent with the results of factor analysis. The fruit quality of‘Gold Nugget'‘Shasta Gold'‘Tahoe Gold'and‘Yosemite Gold'were excellent in fruit quality, while‘Shasta Gold'and‘W. Murcott'were inferior to the other four cultivars in fruit quality.【Conclusion】This study showed that factor analysis combined with cluster analysis provide a more comprehensive evaluation for highquality citrus cultivar selection.