Camellia oleifera is the dominant woody oil crop in China. According to current records, the cultivation history of C. oleifera as an oil crop may be less than 1,000 years, and the Yangtze River Basin may be one of the earliest cultivation areas. Wild relatives of C. oleifera are valuable genetic resources for breeding. Camellia oleifera belongs to Sect. Oleifera of the genus Camellia in the family Theaceae. Wild relatives of C. oleifera may include species in Sect. Oleifera and Sect. Paracamellia. However, the division of Sect. Oleifera and Sect. Paracamellia is still under debate, and the phylogenetic relationships among species remain unresolved. Sect. Oleifera and Sect. Paracamellia have the highest frequency of polyploids in the genus Camellia, and the same species may have various ploidies, which may be promoted by artificial selection and interspecies hybridization. The Yangtze River Basin is the main production area of C. oleifera, and the main distribution area of wild C. oleifera, thus containing rich genetic resources of wild C. oleifera. This study analyzed the distribution of species in Sect. Oleifera and Sect. Paracamellia of the genus Camellia and •综述• © 第 4 期 秦声远等: 油茶栽培历史与长江流域油茶遗传资源 385 综述 compared the results with the potential distribution areas of wild C. oleifera. Results show that drainage divides between the Yangtze River Basin and Pearl River Basin (Nanling Mountain, Miaoling Mountain, and adjacent regions) have the highest diversity of species in Sect. Oleifera and Sect. Paracamellia. Meanwhile, these regions are also potential highly suitable growing regions for wild C. oleifera, where there may be potential interspecies hybrid zones between C. oleifera and its wild relative species. Species diversity decreases from the south to the north, likely representing the dispersal direction from south to north. The potential interspecies hybrid zones between C. oleifera and its wild relative species may contain rich genetic diversity and provide natural breeding stations for selective breeding. These regions should be priority areas for research and conservation in order to explore and utilize genetic resources with important economic values.

Conventional microsatellite (simple sequence repeat, SSR) genotyping methods cannot accurately identify polyploid genotypes leading to allele dosage uncertainty, introducing biases in population genetic analysis. Here, a new SSR genotyping method was developed to directly infer accurate polyploid genotypes. The frequency distribution of SSR sequences was obtained based on deep‐coverage high‐throughput sequencing data. Corrections were performed accounting for the “stutter peak” and amplification efficiency of SSR sequences. Perl scripts and an online SSR genotyping tool “SSRSeq” were provided to process the sequencing data and output genotypes with corrected allele dosages. Hexaploid Camellia oleifera is the dominant woody oilseed crop in China. Understanding the geographical pattern of genetic variation in wild C. oleifera is essential for the conservation and utilization of genetic resources. Six wild C. oleifera populations were sampled across geographical ranges in subtropical evergreen broadleaf forests of China. Using 35 SSR markers, the high‐throughput sequencing‐based SSRSeq method was applied to obtain accurate hexaploid genotypes of wild C. oleifera. The results demonstrated that the new method could resolve allele dosage uncertainty and considerably improve genetic diversity, structure and differentiation analyses for polyploids. The genetic variation patterns of wild C. oleifera across geographical ranges agree with the “central‐marginal hypothesis”, stating that genetic diversity is high in the central population and declines from the central to the peripheral populations, and genetic differentiation increases from the centre to the periphery. This method and findings can facilitate the utilization of wild C. oleifera genetic resources for the breeding of cultivated C. oleifera.

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The evergreen versus deciduous leaf habit is an important functional trait for adaptation of forest trees and has been hypothesized to be related to the evolutionary processes of the component species under paleoclimatic change, and potentially reflected in the dynamic history of evergreen broadleaved forests (EBLFs) in East Asia. However, knowledge about the shift of evergreen versus deciduous leaf with the impact of paleoclimatic change using genomic data remains rare. Here, we focus on the Litsea complex (Lauraceae), a key lineage with dominant species of EBLFs, to gain insights into how evergreen versus deciduous trait shifted, providing insights into the origin and historical dynamics of EBLFs in East Asia under Cenozoic climate change. We reconstructed a robust phylogeny of the Litsea complex using genome‐wide single‐nucleotide variants (SNVs) with eight clades resolved. Fossil‐calibrated analyses, diversification rate shifts, ancestral habit, ecological niche modelling and climate niche reconstruction were employed to estimate its origin and diversification pattern. Taking into account studies on other plant lineages dominating EBLFs of East Asia, it was revealed that the prototype of EBLFs in East Asia probably emerged in the Early Eocene (55–50 million years ago [Ma]), facilitated by the greenhouse warming. As a response to the cooling and drying climate in the Middle to Late Eocene (48–38 Ma), deciduous habits were evolved in the dominant lineages of the EBLFs in East Asia. Up to the Early Miocene (23 Ma), the prevailing of East Asian monsoon increased the extreme seasonal precipitation and accelerated the emergence of evergreen habits of the dominant lineages, and ultimately shaped the vegetation resembling that of today.