Hybridization of Lycium qingshuiheense and L. ningxiaense revealed using morphological, SSR markers, and chloroplast...

Lycium has economic and ecological significance, but its natural hybridization has received little attention. Lycium qingshuiheense and L. ningxiaense exhibit intermediate morphological traits between or blended with L. barbarum and L. ruthenicum, inferring their potential hybrid origin. To clarify this hypothesis, the present study investigated their hybridization using morphological traits, nuclear simple sequence repeats (SSRs) markers, and chloroplast genomic data.

Comparative morphological analysis clearly distinguished L. barbarum from L. ruthenicum based on petiole length, leaf morphology and fruit color. In contrast, most L. qingshuiheense and L. ningxiaense individuals exhibited intermediate traits between L. barbarum and L. ruthenicum, although some L. ningxiaense individuals overlapped morphologically with L. ruthenicum. The genetic composition of all L. qingshuiheense and L. ningxiaense individuals represented a genetic mix of the two parent species, all of which are hybrids. The maximum likelihood (ML) and bayesian inference (BI) analyses based on the chloroplast genome revealed nearly congruent topologies, providing a strongly supported (BS = 100%; PP = 1) for a shared clade comprising L. qingshuiheense, L. ningxiaense, and L. ruthenicum.

Based on analyses of morphological traits, SSR markers, and cp. genome data, L. qingshuiheense and L. ningxiaense are likely hybrids resulting from out-crossing between L. ruthenicum and L. barbarum. However, genetic composition of L. qingshuiheense is derived from approximately 85% L. ruthenicum and 15% L. barbarum, Similarly, the variant of L. ningxiaense shows a genetic composition consisting of 40% derived from L. ruthenicum and 60% from Lycium barbarum. The present study elucidated the origin of two Lycium species, which enhances our understanding of the evolutionary mechanisms underlying interspecific hybridization in Lycium. These findings clarify the evolutionary history of these taxa, as well as provide molecular tools and genetic insights for developing improved Lycium varieties with desirable agronomic traits.