Genetic diversity evaluation and germplasm identification of Mesona chinensis Benth from plant morphology, cytology, and EST-SSR molecular markers

Mesona chinensis Benth (MCB), also known as Platostoma palustre, is a highly significant medicinal and edible plant in China and Southeast Asian countries. The cultivated seedlings of MCB are primarily local farm varieties propagated through cuttings, with many being domesticated from wild species. This has led to an unclear and mixed source, as well as uneven quality of MCB. Hence, it is imperative to collect, preserve, evaluate, and identify the germplasm resources of MCB. This study aimed to evaluate the genetic diversity and identify the germplasm of eight core MCB resources using morphology, cytology, and EST-SSR molecular markers. Morphological observations showed significant variation in the inflorescences, leaves, stems, and corolla tissues. Scanning electron microscope (SEM) observations demonstrated significant differences in the number of stomata between the abaxial and adaxial sides of leaves. Furthermore, out of 192 primer pairs of EST-SSR molecular markers, 9 were suitable for constructing fingerprints. A total of 31 alleles were detected, with an average of 3.444 alleles per locus. The number of effective alleles (Ne) of 9 EST-SSR loci ranged from 1.473 (TDF139) to 3.877 (TDF166), while the Shannon Information index (I) per locus ranged from 0.601 (TDF139) to 1.461 (TDF166). The average value of observed heterozygosity (Ho) was 0.681, while the expected heterozygosity (He) was 0.523. The mean value of fixation index (F) was -0.294, while the mean heterozygosity within populations (Hs) was 0.762. The polymorphism information content (PIC) ranged from 0.295 (TDF139) to 0.701 (TDF166) across the 9 loci, with an average PIC value of 0.466. These results indicated that the selected EST-SSR primers exhibited high levels of polymorphism. Notably, TDF166 played a prominent role in exploring the genetic diversity of MCB. Furthermore, the Nei’s genetic distance among the eight germplasm resources exhibited significant variation, resulting in the division of all germplasm resources into six subclades. This suggested the presence of abundant genetic diversity within the MCB germplasm resources used in this study. This study provided a foundation for the conservation, management, and future breeding of MCB germplasm resources.