Analysis of fruit and seed phenotypic diversity in different sea buckthorn germplasms

【Objective】The collection, evaluation, and rational utilization of sea buckthorn germplasm resources form the foundation for breeding superior varieties and developing effective production practices. Qinghai Province possesses an abundance of sea buckthorn germplasm resources. This study aimed to investigate the genetic diversity of fruit and seed phenotypic traits among local and introduced sea buckthorn varieties in alpine region of Qinghai, with the objective of identifying germplasm exhibiting exceptional seed and fruit characteristics.【Methods】This study systematically evaluated the phenotypic traits of fruits and seeds from 36 sea buckthorn germplasm samples collected in alpine region of Qinghai. The aim was to establish a reference for assessing fruit quality, improving germplasm breeding, and supporting the sustainable development of the sea buckthorn industry in Qinghai Province. Evaluated quality traits included fruit shape, seed shape, seed coat color, and grooves, while quantitative traits encompassed berry stalk length, berry longitudinal and transverse diameters, berry shape index, berry volume, single berry weight, seed length and width, seed shape index, seed volume, 1000- grain weight, exocarp and endocarp mass, as well as exocarp and endocarp thickness. Subsequent analyses included diversity, correlation, and cluster analyses of these phenotypic traits, culminating in a comprehensive evaluation through principal component analysis.【Results】The fruits and seeds of 36 sea buckthorn germplasms exhibited significant genetic diversity, with quality traits showing a diversity in- dex ranging from 0 to 1.14. Fruit shapes displayed the highest variation types and the largest diversity index, while seed grooves exhibited the smallest diversity index, present in all germplasm seeds. It indicated that the distribution of this trait was relatively stable among different description types. Among the 36 sea buckthorn germplasms, oblate ones were the most common, accounting for 40.74%, followed by round ones, accounting for 38.43%, and cylinder ones had the lowest proportion, only 2.78%. The coefficient of variation for the 15 quantitative traits varied from 11.46% to 68.42%. Notably, exocarp thickness and endocarp mass demonstrated substantial variation, with coefficients of variation exceeding 60%, and berry stalk length, berry volume, single berry weight, seed volume, exocarp mass, and endocarp thickness, were all above 30%, indicating considerable dispersion of phenotypic traits among different sea buckthorn germplasms. The diversity index for quantitative traits ranged from 1.25 to 2.08. Berry stalk length, berry transverse diameter, single fruit weight, seed length and width, seed shape index, seed volume, 1000-grain weight, and endocarp thickness all exhibited diversity indices exceeding 2.00, classifying them as highly variable traits. The genetic diversity index for the remaining traits fell between 1.00 and 2.00. The correlation analysis revealed intricate and strong correlations among diverse phenotypic traits in different sea buckthorn germplasms. Subsequent cluster analysis categorized 36 sea buckthorn germplasm resources into three distinct groups: the first group featured medium-sized fruits with thin and light fruit skins; the second group exhibited small fruits with thick fruit skins; the third group showcased large fruits with elongated fruit stalks. The principal component analysis demonstrated that the cumulative contribution rate of the three principal components identified was 80.011%. Specifically, the first principal component primarily reflected the quality and shape of fruits and seeds, the second principal component predominantly characterized the exocarp thickness, and the third principal component was mainly associated with the endocarp thickness. The comprehensive assessment indicated that the highest overall score was recorded in 2013- 05 (5.510).【Conclusion】The variation in fruit and seed quality traits among sea buckthorn germplasms in alpine region of Qinghai is relatively extensive, and the diversity index for quantitative traits is notably high. Through a combination of correlation analysis and principal component analysis, five key indicators for assessing sea buckthorn plant traits are identified: berry longitudinal diameter, seed length, single fruit weight, 1000-grain weight, and berry peel thickness. These indicators can serve as crucial reference points for subsequent quality analysis, evaluation of sea buckthorn germplasm resources, and variety breeding efforts. The comprehensive scores of fruit and seed phenotypic traits of six sea buckthorn germplasms namely 2013-05, Zayou No. 2, Fuza, LJ-10-03, LJ-10-56, and Zayou No. 1, rank among the highest as a result of integrating various evaluation methods, and are suitable for breeding sea buckthorn varieties and for the rational development and utilization in alpine region of Qinghai.