Hybridization and introgression of two sympatric Lycium species revealed by simple sequence repeat (SSR) markers

Hybridization and introgression are important ways to promote genetic variation and play important roles in the evolution of species. Two sympatric Lycium populations, L. ruthenicum and L. barbarum, are found in the Qiadam Basin. In this study, we sampled 30 trees and analyzed the phenotypic characteristics of tree shape, leaf type, and fruit type. In addition, we analyzed these samples using generic simple sequence repeat (SSR) markers. The molecular marker data revealed that direct gene flow between the two Lycium species was fairly low, while the gene flow between hybrids and parents was greater; therefore, the majority of gene introgression was intermediate because of the backcrossing of hybrids with the two parents. Structure analysis revealed that L. ruthenicum maintained a stricter genetic boundary than did L. barbarum, and compared with L. ruthenicum, L. barbarum was found to backcross with the hybrids more intensively, consistent with the fruit morphological observation. The introgression ability of the studied alleles varied across species, with some being completely blocked from interspecific introgression. Our study provides a theoretical foundation for Lycium breeding and a practical example for understanding the evolution of Lycium species.