Genetic structure and biogeographic divergence among Sapindus species: An inter-simple sequence repeat-based study of germplasms in China

Sapindus mukorossi and Sapindus delavayi are widely distributed in China, and their fruits are very valuable because they contain specific, economically useful plant oils and saponins. There are relatively few published studies about these two species' genetic structure, suitable planting areas, and variations in economically important fruit traits. The objectives of this study were to evaluate the genetic structure of germplasms selected from a wide region, determine suitable growth conditions, and characterize variability among economically important fruit traits based on genotypes. We analyzed samples using inter-simple sequence repeats (ISSRs) and detected 247 loci by scanning the genetic diversity of 61 Sapindus germplasms with 16 ISSR primers. The unweighted pair group method with arithmetic mean and the STRUCTURE program were used to predict the genetic structure among species and S. mukorossi germplasms, respectively. A principal component analysis was completed to examine the correlations between genetic diversity and ecological factors. The S. mukorossi and S. delavayi germplasms were divided into two groups, and the S. mukorossi germplasms were further divided into two subgroups, with clear genotypic differences. The distributions of the Sapindus germplasms indicated that S. delavayi can adapt to high elevations, while S. mukorossi subgroup 1 germplasms can adapt to moderate precipitation and low temperatures better than the subgroup 2 members. Additionally, the S. mukorossi subgroup 2 germplasms can adapt to relatively large changes in precipitation and low temperatures. Moreover, correlation analyses suggested that subgroup 1 germplasms exhibit phenotypic plasticity and the potential to produce oils. These observations may have implications for tree breeding programs. Furthermore, the distribution patterns of the genetic diversity reported herein may provide relevant baseline data for the development of conservation strategies applicable to related wild-type tree species.