Phenotypic diversity analysis of 98 olive germplasm accessions in Longnan

【Objective】Olive (Olea europaea L.), a Mediterranean- native evergreen tree belonging to the family Oleaceae, has been cultivated in China for approximately six decades since its introduction in the 1950s. The Longnan Olive National Forest Tree Germplasm Repository, located in Gansu Province, has amassed over 160 olive varieties, establishing a rich and diverse germplasm resource base. Notwithstanding the substantial accumulation of germplasm resources in Olea europaea L., challenges persist in the systematic evaluation and strategic exploitation of these genetic repositories. This investigation undertakes a comprehensive characterization of phenotypic divergence in foliar and pomological characteristics across diverse olive genotypes, seeking to establish a theoretical foundation for germplasm innovation and agricultural deployment. The elucidation of intraspecific phenotypic heterogeneity constitutes a critical prerequisite for advancing genetic improvement initiatives, refining agronomic management strategies, and ultimately directing toward the dual objectives of enhancing both yield potential and fruit quality metrics in modern oleiculture.【Methods】Between May and November 2024, a comprehensive investigation was conducted at the Longnan Olive National Forest Tree Germplasm Re-pository. In the study, 14 phenotypic traits related to fruits and leaves in 98 olive germplasm accessions were analyzed, which were grafted onto“Chenggu 18a”rootstocks in 2019. The experimental site was situated in the Bailongjiang River Valley of Wudu District, Longnan City, Gansu Province. This region is characterized by an annual average temperature of 14.2 ℃, annual precipitation of 551.2 mm, and an altitude of 1079 meters. Each of the 98 germplasm accessions was grafted onto four trees, with a planting distance of 3 m × 3 m, and all trees were managed uniformly to ensure consistent growth conditions. For leaf trait measurement, healthy leaves were randomly selected from the east, south, west, and north sides of each tree crown. The selected leaves were measured for length, width, thickness, and leaf spacing. For fruit trait measurement, 30 disease- free mature fruits were randomly collected from each tree crown at fruit maturity. These fruits were measured for vertical diameter, transverse diameter, pulp thickness, and mass. Additionally, the seeds were weighed, and their vertical and transverse diameters were measured. Data analysis was performed using Microsoft Excel 2019 to calculate the coefficient of variation (CV) and Shannon-Wiener index (H′ ). Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were employed to reduce data dimensions and classify the germplasm accessions. Multiple comparisons and correlation analyses were conducted to comprehensively evaluate the phenotypic traits of olive germplasm accessions and reveal their genetic diversity. These methods allowed for a detailed assessment of the phenotypic variation and diversity within the studied germplasm accessions.【Results】The 98 olive germplasm accessions from Longnan exhibited significant variation in leaf and fruit phenotypic traits, indicative of high genetic diversity. The predominant leaf shape was elliptic-lanceolate (90.82%), followed by elliptic (7.14%), with lanceolate and ovate shapes being relatively rare (2.04%). Variation coefficients for leaf tip shape, leaf base shape, and leaf bending direction exceeded 30%, while that for leaf shape was 14.88%. The variation coefficients for five quantitative leaf traits ranged from 13.69% to 18.43% , with the smallest coefficient observed for leaf length (13.69%), and spanning a range of 42.25-87.06 mm. These results suggested that leaf length was relatively stable across the studied germplasm accessions, while other leaf traits exhibited higher variability. Fruit shapes were predominantly elliptic and oblong (44% ), followed by round (12% ) and obovate (10% ). Significant differences in single fruit mass were noted among different fruit shapes, with the lightest average mass recorded for olive-shaped fruits (1.89 g) and the heaviest for curved fruits (4.49 g). Variation coefficients for six quantitative fruit traits ranged from 8% to 52%, with the highest coefficient for single fruit mass (52%) and the lowest for pulp rate (8%). These findings highlighted the substantial variation in fruit traits, particularly in fruit mass, which may have significant implications for olive breeding and production. Significant variation was observed among the 14 phenotypic traits, with Shannon- Wiener indices (H') ranging from 4.55 to 5.90 and variation coefficients from 8.00% to 57.79% (mean 33.98%). These results underscored the rich genetic diversity among these traits, indicating a broad potential for phenotypic variation and adaptation. Principal component analysis reduced the 14 phenotypic traits to six main components, accounting for a cumulative contribution rate of 83.327% and reflecting the key characteristics of the olive germplasm accessions. These components effectively captured the essential phenotypic information, providing a simplified yet comprehensive representation of the germplasms' traits. Cluster analysis categorized the 98 germplasms into three distinct groups. GroupⅠ featured larger fruits and higher pulp rates, suggesting potential for enhanced fruit size and oil content. Group Ⅱ exhibited larger leaves and smaller single fruit mass, indicating potential advantages in environmental adaptability. Group Ⅲ was characterized by larger leaf spacing and medium- sized fruits, suggesting potential for managing canopy density and boosting photosynthetic efficiency. Theseclassifications provide a clear framework for understanding the phenotypic diversity and potential applications of the studied germplasm accessions.【Conclusion】The 98 olive germplasm accessions from Longnan exhibited substantial phenotypic variation in leaf and fruit characteristics, demonstrating significant genetic diversity for olive improvement programs. Cluster analysis delineated three distinct germplasm groups with specialized breeding potentials. GroupⅠ accessions displayed superior fruit dimensions and elevated oil yield characteristics, positioning them as prime candidates for developing high-oil-content cultivars. Group Ⅱ manifested adaptive traits including expanded leaf morphology and compact fruit architecture, suggesting their utility in breeding programs targeting environmental resilience. Group Ⅲ exhibited optimal leaf spatial arrangement coupled with moderate fruit parameters, offering prospects for optimizing canopy architecture and photosynthetic performance to enhance overall productivity. This systematic classification provides a strategic framework for precision breeding in olive genetic improvement.