Abstract: 【Objective】The DUS (Distinctness, Uniformity and Stability) test refers to the process of testing the specificity, consistency and stability of new plant varieties, the DUS test guideline is the technical basis and standard for DUS test of tested varieties, and has become the technical basis for variety approval, variety registration and variety protection in China. At present, the DUS testing guideline of Citrus in China (NY/T 2435-2013), covers the entire Citrus genus. However, there are great differences in some characteristics between the same genus and different species. Therefore, this study aimed at pomelo varieties to explore the adaptability of quantitative characteristics in the DUS testing guidelines for Citrus in China to pomelo varieties, and to provide reference for more objective and scientific description of quantitative characteristics of from 9 levels to 7 levels, and the petal index, leaf shape index, central column size, capsule number, juice content and soluble solids decreased from 9 levels to 5 levels. For fruit weight, fruit length and fruit diameter, the grading standards of pomelo and grapefruit were formulated respectively.The Shannon diversity index of each characteristics under this grading standard ranges from 0.878 to 1.954, and the Shannon diversity index of fruit juice acidity was relatively large, indicating that this characteristics had more phenotypes and was evenly distributed in different grades. The correlation coefficient of twenty-five quantitative characteristics ranged from -0.69 to 0.91, and the correlation coefficient between fruit diameter and fruit weight was the highest, reaching 0.91, showing a very significant positive correlation; Six principal components were obtained by principal component analysis, with a cumulative contribution rate of 72.76%. The first principal component contained the most information, which was mainly determined by 11 characteristics, including fruit diameter, fruit weight, fruit length, petal width, calyx diameter, petal length, core diameter,stamens number per flower, juice vesicles length, leaf blade width and number of seeds.【Conclusion】This study has established a preliminary classification index for twenty-five quantitative characteristics of pomelo germplasm resources, which has certain guiding significance for the evaluation, utilization, and breeding of pomelo germplasm resources. At the same time, it provides reference for the identification of pomelo germplasm and the revision of pomelo DUS testing guideline in China. In addition, the classification standard of this study is based on the growth of pomelo in Chongqing, and the specific classification range may not be fully applicable to other ecological regions. In the process of DUS testing, researchers need to make corresponding adjustments according to the expression status of standard varieties and combined with the field conditions, so as to ensure accurate evaluation and comparison of the character differences of varieties in different regions.pomelo and revision of DUS test guidelines of Citrus.【Methods】In this study, twenty-five quantitative characteristics of 117 pomelo germplasm resources in the national Citrus germplasm resource nursery were observed according to the DUS testing guideline of Citrus in China. The data of these twenty-five quantitative characteristics were collected by measurement method. The normality of the data was comprehensively judged according to the significant test value of the K-S test for each quantitative characteristics, the fitting of the frequency distribution diagram and the normality curve, and the deviation between the measured value of the Q-Q diagram and the predicted normal value. The least significant difference method is used to grade the quantitative characteristics that conform to the normal distribution, and the range method is used to grade the quantitative characteristics that do not conform to the normal distribution.【Results】The intra-variety variation coefficient of twenty-five quantitative characteristics was between 2.96% and 29.96%, and the inter-variety variation coefficient was between 10.33% and 62.90%. Most quantitative characteristics showed great polymorphism and stability.According to the results of normality test,petal length, petal length/width, leaf blade length, leaf blade length/ width, petiole length, petiole wing width, stylar scar diameter, core diameter, fruit rind thickness, number of segments per fruit, number of seeds, fruit juiciness, total soluble solids, fruit juice acidity and edible rate conformed to normal distribution; The length of spring shoot internode, petal width, stamens number per flower and leaf blade width conformed to the approximate normal distribution; Calyx diameter, fruit lengt, fruit diameter, fruit length/diameter, juice vesicles length and single-fruit weight did not conform to normal distribution. Among the six quantitative characteristics that did not follow a normal distribution, it was found that the frequency distribution of fruit weight, fruit lengt and fruit diameter showed a clear bimodal distribution, which was mainly caused by the significant differences between pomelo and grapefruit species. Grapefruit belongs to small fruits while pomelo belongs to large fruits, and the two show significant differences in these three characteristics, leading to a bimodal distribution. Therefore, if pomelo and grapefruit are uniformly graded on these quantitative characteristics, it will lead to a wide grading range and misjudge varieties with differences as no differences, thereby increasing the probability of errors occurring. This study developed different grading standards for pomelo and grapefruit based on these three characteristics. After separating the data of the two species based on the three quantitative characteristics mentioned above, it was found that except for the pomelo group whose data on fruit diameter did not follow a normal distribution, the rest basically followed a normal distribution or approximate normal distribution. The least significant difference method was used to grade the quantitative characteristics that conformed to the normal distribution, and the range method was used to grade the quantitative characteristics that did not conformed to the normal distribution. The classification criteria of twenty-five quantitative characteristics were obtained. Compared with the grading numbers in the DUS testing guideline of Citrus in China, the calyx diameter, fruit shape index and juice cell length increased from 3 levels to 5 levels, the petal length, petal width, leaf length, leaf width and pericarp thickness decreased
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