Research on genetic diversity and mating patterns of Toona fargesii populations based on SSR markers

Toona fargesii is a rare and endangered tree species. Investigating genetic diversity and mating patterns is critical for unraveling the evolutionary trajectory, adaptive strategies, and germplasm conservation of this species. In this study, a total of 169 samples were analyzed, including 78 adult clones and 91 offsprings of T. fargesii. Additionally, nine clones of another tree species (T. sinensis) were exclusively used for mating pattern analysis. 17 microsatellite markers were employed to determine the outcrossing rate, paternal contribution, and pollination distance of the breeding population, while 12 microsatellite markers with high data retention rates were selected to assess the genetic diversity of T. fargesii populations. We found that the genetic diversity of both the breeding and offspring populations was low. For expected heterozygosity (He), the breeding population had a value of 0.475, while the offspring population exhibited a lower He of 0.417. Parental analysis of offspring showed that T. fargesii predominantly relies on outcrossing. The breeding population exhibited a selfing rate of 14.63% and an outcrossing rate of 85.37%. Significant variations were observed in paternal contributions across the breeding population. Among all adult clones, MHC001 exhibited the highest paternal contribution, accounting for 19.51%. Most pollination events occurred within 80 m, although the maximum recorded distance extended to 158.97 m. MHC001 produced a significantly greater number of fruits compared to the other 10 sampled trees. These results have an important role in population conservation. This study provides an in-depth assessment of the current status of T. fargesii populations and lays a foundation for improved conservation and utilization strategies of its germplasm resources.