The Chinese elm is an important tree ecologically; however, little is known about its genetic diversity and adaptation mechanisms. In this study, a total of 107 individuals collected from seven natural populations in eastern China were investigated by specific locus amplified fragment sequencing (SLAF-seq). Based on the single nucleotide polymorphisms (SNPs) detected by SLAF-seq, genetic diversity and markers associated with climate variables were identified. All seven populations showed medium genetic diversity, with PIC values ranging from 0.2632 to 0.2761. AMOVA and Fst indicated that a low genetic differentiation existed among populations. Environmental association analyses with three climate variables (annual rainfall, annual average temperature, and altitude) resulted in, altogether, 43 and 30 putative adaptive loci by Bayenv2 and LFMM, respectively. Five adaptive genes were annotated, which were related to the functions of glycosylation, peroxisome synthesis, nucleic acid metabolism, energy metabolism, and signaling. This study was the first on the genetic diversity and local adaptation in Chinese elms, and the results will be helpful in future work on molecular breeding.

No abstract

Carya ovata is a slow-growing, long-lived deciduous species that belongs to section Carya of genus Carya. In this study, we de novo assembled the complete chloroplast genome of C. ovata, and analyzed its phylogenetic relationship. The circular genome was 160,765 bp in length, comprising a large singlecopy region (89,975 bp), a small single-copy region (18,788 bp), and a pair of inverted repeat regions (26,001 bp each). The chloroplast genome was predicted to contain 131 genes, including 83 proteincoding genes, 40 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Overall, the GC content of the chloroplast genome was 36.16%. Phylogenetic analysis suggested that C. ovata was closely related to C. illinoinensis, a representative of section Apocarya within the genus Carya.

Koelreuteria bipinnata is an important ornamental tree with attractive flowers and fruits. In this study, we used next-generation sequencing technology to obtain the complete chloroplast genome of K. bipinnata. The entire genome was determined to be 163,863 bp in size, harboring a typical quadripartite structure with a large single copy (LSC) region of 90,240 bp, a small single copy (SSC) region of 18,883 bp, and a pair of 27,370 bp inverted repeat (IR) regions. The genome was predicted to contain 132 genes, including 84 protein-coding genes, 40 tRNA genes, and 8 rRNA genes. The overall GC content of K. bipinnata chloroplast genome was 37.29%. Phylogenetic analysis based on complete chloroplast genome sequences indicated that K. bipinnata was closely related to K. paniculate. This study would be useful for future population genetics studies and phylogenetic analysis of K. bipinnata.

Zelkova schneideriana is a highly valued tree species belonging to the Ulmaceae family. It can be used as a precious timber tree for large-scale planting because of its highdensity wood (Huang et al. 2019; Zhang et al. 2022). This species is also an important ornamental plant due to its graceful crown, straight trunk, and attractive leaves (Jin et al. 2009). Additionally, the bark and leaves of Z. schneideriana are especially significant in Chinese traditional medicine (Shao and Zhang 2021). Given the versatile application of Z. schneideriana, it has been overharvested over the past few decades in China (Shao and Zhang 2021). Moreover, because of its poor natural regeneration (Carra et al. 2019), the population of Z. schneideriana in the wild has been decreasing (Sun et al. 2020). Since 1999, Z. schneideriana has been listed as a national second-grade protected plant species in China (Shao and Zhang 2021).Generally, Z. schneideriana has a large crown (Liu et al. 2014), occupying a large planting space. In a limited area, the cultivated density could be highly increased by selecting cultivars that have small canopy diameter. In China, there is a limited space for planting trees. Therefore, Z. schneideriana with a small crown is in high demand. To alleviate this need, we performed breeding programs for selecting Z. schneideriana cultivars with a small crown. In 2016, we released a new cultivar named 'Chongtian', which exhibited small-angle branching.