Floral and pollen diversity of Camellia rosthorniana germplasm accessions from Fanjing Mountain region: systematic significance and germplasm utilization

Floral and pollen morphological variation and distribution patterns in Camellia rosthorniana Hand.-Mazz. germplasms from the Fanjing Mountain region were analyzed from both quantitative and qualitative perspectives. This study aims to provide preliminary morphological data that may support future varietal classification, conservation efforts, and the potential utilization of these regional genetic resources. Floral measurements were obtained using a vernier caliper, while pollen morphology was examined through scanning electron microscopy (SEM) and quantitatively analyzed with ImageJ software. Several analytical methods, including the coefficient of variation (CV) and correlation analysis, were applied to evaluate phenotypic diversity and variation. Principal component analysis (PCA) and cluster analysis were performed to assess phenotypic structure, while orthogonal partial least squares-discriminant analysis (OPLS-DA) was specifically employed to identify the key discriminatory traits contributing to group differentiation. Significant variation was observed in floral traits, with the Shannon-Wiener diversity index ( H ’) ranging from 0.22 to 2.76, with corolla length showing the highest diversity index and pistil number the lowest. CV values ranged from 7.21% to 23.80%, with pistil number exhibiting the least variation and stamen number the greatest. Pollen grains were oblong in the equatorial view and trilobate-circular in the polar view. For pollen traits, the H ’ ranged from 1.42 to 1.91, and the CV varied from 4.76% to 45.09%. The exine ornamentation displayed granulate-foveolate, representing a distinct palynological characteristic of these accessions. Correlation analysis showed stronger associations among floral traits than between floral and pollen traits. Notably, ovule number was negatively correlated with colpus length, while petal number was negatively correlated with equatorial axis length. PCA identified six principal components, which accounted for 72.973% of the total variance. Cluster analysis (Euclidean distance, linkage distance L = 11) grouped the germplasms into three major clusters. OPLS-DA pinpointed six key discriminatory variables: ovule number, equatorial axis length, corolla length, P/E ratio, polar axis length, and petal number. Box plot analyses revealed significant morphological variation among the three clusters across eight floral and pollen traits. Frequency distribution patterns of specific stamen traits reveal a numerical shift that suggests a potential phenotypic tendency toward stamen-to-petal transformation. In vitro germination tests revealed that Clusters I and II both maintained high average germination rates (exceeding 70%), with no significant difference between them. However, Cluster II exhibited greater germination stability and more consistent distribution compared to Clusters I and III. This study provides a comprehensive morphological characterization of C. rosthorniana germplasm from the Fanjing Mountain region. The results reveal significant intraspecific variation, offering preliminary morphological evidence for germplasm differentiation and serving as a potential reference for identifying candidate germplasm resources for ornamental Camellia breeding, contingent upon further genetic and field validation.