Identification of a Natural Hybrid betweenCastanopsis sclerophyllaandCastanopsis tibetana(Fagaceae) Based on Chloroplast and Nuclear DNA Sequences

Castanopsis x kuchugouzhuiHuang et Y. T. Chang was recorded in Flora Reipublicae Popularis Sinicae (FRPS) as a hybrid species on Yuelushan mountain, but it is treated as a hybrid betweenCastanopsis sclerophylla(Lindl.) Schott. andCastanopsis tibetanaHance in Flora of China. After a thorough investigation on Yuelushan mountain, we found a population ofC. sclerophyllaand one individual ofC. x kuchugouzhui, but no living individual ofC. tibetana. We collectedC. x kuchugouzhui, and we sampled 42 individuals ofC. sclerophyllafrom Yuelushan and Xiushui and 43 individuals ofC. tibetanafrom Liangyeshan and Xiushui. We used chloroplast DNA sequences and 29 nuclear microsatellite markers to investigate ifC. x kuchugouzhuiis a natural hybrid betweenC. sclerophyllaandC. tibetana. The chloroplast haplotype analysis showed thatC. x kuchugouzhuishared haplotype H2 withC. sclerophyllaon Yuelushan. The STRUCTURE analysis identified two distinct genetic pools that corresponded well toC. sclerophyllaandC. tibetana, revealing the genetic admixture ofC. x kuchugouzhui. Furthermore, the NewHybrids analysis suggested thatC. x kuchugouzhuiis an F2 hybrid betweenC. sclerophyllaandC. tibetana. Our results confirm thatC. x kuchugouzhuirecorded in FRPS is a rare hybrid betweenC. sclerophyllaandC. tibetana.