Comprehensive evaluation of genetic diversity and morphological traits of Xinjiang wild jujube (Ziziphus jujuba var. spinosa) germplasm resources

【Objective】Ziziphus jujuba var. spinosa, native to China, shows strong adaptability to drought, infertile soil, and other harsh environments. It is an important shrub for soil and water conservation in arid hilly regions and an excellent rootstock for cultivated jujube trees. Its fruits, seeds, leaves, and flowers also have medicinal value. In Xinjiang, an arid distribution area of this species, wild populations have developed high adaptability to desert drought and large temperature differences through long - term natural selection, containing unique region - specific stress - resistant genes. However, unlike in Hebei, Henan, and Ningxia, where systematic germplasm collection and evaluation have been carried out, such work is lacking for Xinjiang wild Jujube (Z. jujuba var. spinosa). Consequently, its morphological diversity, patterns of phenotypic variation, and potential utilization value remain poorly understood, which limits efficient resource utilization and scientific conservation. This study aimed to systematically analyze the phenotypic diversity of Z. jujuba var. spinosa germplasm from six regions in Xinjiang, establish a multi - trait comprehensive evaluation system, identify superior germplasm with special economic traits or ecological adaptation potential, and provide a theoretical basis and high - quality breeding materials for resource conservation, innovation, utilization, and the development of a characteristic fruit industry.【Methods】Between August and October 2024, field sampling was carried out in six regions of the Xinjiang Uygur Autonomous Region, and 162 Z. jujuba var. spinosa germplasm resources were selected as experimental materials. Sampling sites were georeferenced using GPS, and germplasms were uniformly numbered. Trait measurements followed standardized protocols: Ten robust secondary branches from the middle - lower outer crown were used for branch and thorn measurement; fruiting shoots from the second node of two - year - old fruit spurs were collected for leaf and fruiting shoot measurements; and ten normally developed, similarly sized fruits at the crisp ripe stage from two - year - old spurs were taken for fruit measurements. All traits were measured immediately after sampling. Based on the descriptors and data standards for Jujube germplasm resources and germplasm resources of Chinese Jujube, 24 descriptive traits (e.g., peel thickness, fruit shape) and 24 quantitative traits (e.g., secondary branch length) were recorded. Descriptive traits were categorized into grades. Excel 2024 was used to calculate distribution frequencies and the Shannon - Wiener diversity index (H′). For quantitative traits, Excel 2024 was used to compute the mean, maximum, minimum, standard deviation, and coefficient of variation (CV). SPSS 27 was employed for correlation analysis and principal component analysis (PCA). Origin 2021 was used for generating correlation heatmaps, cluster diagrams, and PCA plots. Standardized data were utilized for PCA. The membership function method was applied to calculate membership value, weight, and comprehensive evaluation D - value for assessing phenotypic traits.【Results】For the 24 descriptive traits, 84 variation types were identified (averaging approximately four per trait). H′ ranged from 0.361 to 2.364 (average 1.275). The highest diversity was observed for fruit shape (2.364), and the lowest was for sepal condition (0.361). Developed thorns, spreading leaves, and an oblique leaf base accounted for 75.93%, 75.31%, and 62.35% of the branch/thorn traits, respectively. Thin peel and round fruit accounted for 75.93% and 41.36% of the fruit traits, respectively. Fruit flavor exhibited six types: extremely sour (3.70%), sour (21.60%), sweet - sour (21.60%), sour - sweet (25.93%), sweet (20.99%), and extremely sweet (6.17%). For 24 quantitative traits, the coefficient of variation (CV) ranged from 5.82% to 51.15%, with the largest variation observed in single fruit weight (51.15%) and the smallest in peel lightness (L*, 5.82%). The average stipular spine length was 4.75 mm (CV = 32.92%, max: 10.82 mm RQ3, min: 1.97 mm TJG15). The average straight spine length was 18.11 mm (CV = 32.59%, max: 43.93 mm LP3, min: 4.82 mm LP12). The average secondary branch length was 20.93 cm (CV = 26.93%); the average number of secondary branch nodes was 7 (CV = 23.56%); the average length of fruiting shoots was 97.27 mm (CV = 29.05%); and the average number of leaves per fruiting shoot was 10 (CV = 24.11% ). The verage leaf length was 27.94 mm (CV = 24.97% ), the width was 14.21 mm (CV = 25.69% ), and the thickness was 0.14 mm (CV = 19.48%). The coefficient of variation (CV) of petiole length was 40.18%, the CV of petiole diameter was 34.79% , and the CV of leaf area was 41.61% . The average relative chlorophyll content was 54.25 (CV = 13.87%). The average fruit equatorial diameter was 15.21 mm (CV = 16.41%), the polar diameter was 16.36 mm (CV = 19.52% ), the stone length was 10.82 mm (CV = 18.55% ), and the stone width was 7.09 mm (CV = 14.61%). The average stone weight was 0.56 g (CV = 34.89%). The single - fruit weight reached a maximum of 7.38 g (QS4) and a minimum of 0.51 g (LP8). The stone weight reached a maximum of 1.44 g (QS9) and a minimum of 0.14 g (LP7). Most quantitative traits showed significant or highly significant correlations. The stipular spine length exhibited a highly significant positive correlation with the straight spine length (P＜0.01) and secondary branch length. Leaf length showed a highly significant positive correlation with leaf width, as well as significant correlations with petiole length, diameter, and chlorophyll content (P＜0.05). The leaf area was significantly correlated with fruit equatorial and polar diameters, and highly significantly correlated with single fruit weight. Fruit equatorial diameter was highly significantly correlated with polar diameter, single fruit weight, peel a*, b*, and C*. Peel a*, b*, and C* values were highly significantly positively correlated with each other. The stone weight was significantly correlated with the stone width and length, and highly significantly correlated with stone diameter. There was a significant negative correlation between secondary branch nodes and the number of leaves per fruiting shoot. Cluster analysis divided the 162 germplasms into six groups. Group Ⅰ (119 resources) contained four subgroups: Ⅰ1 (43 resources such as TKX13, TKX9, TJG15, KR3, with consistent secondary branch nodes and normal full - flesh color); Ⅰ2 (73 resources); Ⅰ3 (2 resources: LP3, LP4, with dark fruit color and glossy luster); Ⅰ4 (1 resource). Group Ⅱ included 30 resources, Group Ⅲ contained 9, Group Ⅳ had 2 (TKX29, YXLM12), Group Ⅴ included 1 (YT6), and Group Ⅵ contained 1 (RQ28). PCA extracted eight principal components (PC1-PC8) with eigenvalues ＞1 (5.803, 3.883, 3.023, 1.668, 1.386, 1.158, 1.074, 1.015), and the cumulative contribution rate was 79.211% . PC1 (24.179% ) was primarily influenced by single fruit weight (loading 0.811) and fruit polar diameter (0.767); PC2 (16.180% ) was influenced by peel L* (0.766) and b* (0.751); PC3 (12.595% ) was influenced by fruiting shoot length (0.587) and secondary branch nodes (0.553). Sixteen representative indicators were screened. The top six individuals ranked by the comprehensive evaluation D- value were: QS4 (2.182 3), QS9 (2.138 5), SF1 (1.474 9), SF2 (1.444 8), YT5 (1.426 1), and YT7 (1.379 7). TJG4 had the lowest D-value (-1.576 4).【Conclusion】This study systematically evaluated the phenotypic diversity of 162 Xinjiang wild Jujube (Z. jujuba var. Spinosa) germplasms. The descriptive traits had 88 variation types, with the fruit shape and stone pattern exhibiting the greatest diversity. Quantitative traits had coefficients of variation (CVs) ranging from 5.82% to 51.15%, with single fruit weight and leaf area being the most variable. The leaf area showed a highly significant positive correlation with single fruit weight (r = 0.82). PCA extracted eight principal components (cumulative contribution rate 79.21%), with PC1 mainly driven by single fruit weight and fruit polar diameter. Six excellent individuals were identified using the membership function method. Xinjiang Wild Jujube (Z. jujuba var. Spinosa) exhibits significant regional specificity in fruit, stone, and leaf traits when compared with those in Hebei and Henan, possibly due to the unique climate, soil, and ecological adaptation. High variation in single fruit weight and excellent individuals offer advantages for fruit size improvement and yield exploration. A significant correlation between leaf area and single fruit weight suggests adaptation to arid environments by regulating leaf photosynthetic area and efficiency, offering special genetic materials for high- photosynthetic- efficiency breeding in arid areas. The screened excellent individuals can be used as core breeding materials.