Exploring phenotypic diversity and constructing a floral core collection of Ziziphus jujuba var. spinosa

Ziziphus jujuba var. spinosa is an ecologically valuable tree species. However, most investigations have concentrated on the leaves and fruits. There is insufficient focus on investigating the phenotypic diversity and morphological characteristics of wild jujube floral organs. This gap in knowledge impedes a comprehensive understanding of floral development, which in turn restricts practical applications such as the enhancement of breeding efficiency and yield in cultivated varieties.

We evaluated 28 floral traits of 205 sour jujube clones from 30 provenances across eight Chinese provinces. Phenotypic variation was assessed using nested ANOVA, coefficient of variation (CV), and Shannon-Wiener index (H'). Pearson correlation analysis was conducted to examine associations between floral traits and climatic and geographic factors. Principal component analysis (PCA) and hierarchical clustering were used to classify breeding groups, and a core collection was established via stepwise clustering.

The results demonstrated significant diversity and variation in the floral organs of sour jujube. The average CV for quantitative and qualitative traits were 25.30% and 37.85%, respectively, while the mean H' for quantitative traits (1.68) was higher than that for qualitative traits (0.81). Variation among provenances was the primary source of phenotypic diversity, with the mean phenotypic differentiation coefficient for the quantitative traits of sour jujube reaching 71.32%. Size-related floral traits, including flower diameter, flower area, and flower disc diameter, were significantly correlated with temperature. These traits exhibited significant negative correlations with mean annual, January, and July temperatures (P < 0.01). Principal component analysis extracted six principal components, collectively accounting for 73.14% of the total variance. Based on phenotypic traits, the 205 clones were classified into five breeding groups: A and B for small- and large-flowered ornamental varieties, C for high-yield potential, and E for nectar-rich types with large disc areas. A specialized core collection of 51 accessions for the study of floral organs was constructed using a stepwise clustering approach. This work provides valuable insights for the evaluation and utilization of sour jujube germplasm.