Objective Carya hunanensis is an endemic and high-quality woody oil germplasm resource in China. This study aimed to systematically reveal the variation patterns and diversity characteristics of fruit traits and kernel oil traits in C. hunanensis, identify characteristic germplasm resources with high oil content and superior quality from specific producing areas, and provide a scientific basis for the conservation of C. hunanensis resources, improved variety breeding, and high-value industrial utilization.

Method A total of 148 C. hunanensis samples collected from six major producing areas in Hunan Province, namely Yongshun, Mingxikou of Yuanling, Yixi of Yuanling, Dujiaping of Yuanling, Guanyindong of Yuanling, and Hongjiang, were used as materials. Morphological measurement, Soxhlet extraction, and gas chromatography were employed to determine fruit traits (green fruit traits and nut traits) and kernel oil traits (oil content and fatty acid composition). The characteristics of kernel fatty acid composition and their geographic distribution differences were clarified, the variation patterns and diversity of fruit and kernel traits in C. hunanensis were revealed, and correlation analysis, principal component analysis, and cluster analysis were further conducted for comprehensive evaluation to identify key differential traits, classify resource types, and screen elite germplasm resources.

Result (1) C. hunanensis from different producing areas had formed relatively stable morphological differentiation in the external features of green fruits and internal nuts, and all measured traits showed varying degrees of variation. Among them, the coefficients of variation for single green fruit mass, single nut mass, and kernel mass were relatively high, indicating that resource differences were not mainly concentrated in green fruit appearance, but were more strongly reflected in nut traits related to kernel utilization value. (2) Significant differences in kernel oil content were observed among producing areas. Materials from Yixi showed significantly higher kernel oil content than those from the other producing areas, Mingxikou and Guanyindong were at relatively high levels, and Yongshun showed the lowest value, indicating that C. hunanensis resources had formed a relatively clear regional differentiation pattern in kernel oil accumulation.(3) The kernel oil of C. hunanensis was dominated by unsaturated fatty acids, with a mean proportion of 90.12%. Oleic acid and linoleic acid were the major fatty acids, and materials from different producing areas mainly exhibited two differentiation patterns, namely a high-oleic-acid type and a relatively high-linoleic-acid type, indicating differences in oil quality. (4) Correlation analysis, principal component analysis, and cluster analysis showed that the key differences among C. hunanensis resources were not simple fluctuations in single traits, but the result of coordinated variation in green fruit and nut phenotypes, kernel percentage, kernel oil content, and fatty acid composition. On this basis, the tested materials could be further classified into different resource types, including a high-oleic-acid small-fruit type, a medium-oleic-acid medium-fruit type, and a high-linoleic-acid elongated-fruit type.

Conclusion Materials of C. hunanensis from different geographic origins showed clear differentiation in green fruit and nut phenotypes, kernel oil content, and fatty acid composition. This differentiation was reflected not only in external morphological variation, but also in differences in nut traits and kernel quality related to kernel utilization value and oil-use quality. Germplasms from Yixi and Guanyindong showed relatively prominent performance in terms of oil content and fatty acid composition, and may be regarded as priority candidates for the exploration of elite oil-use germplasm and improved variety breeding.