Litchi (Litchi chinensis Sonn.), an important fruit tree in tropical and subtropical regions, possesses substantial economic value. The branch- and leaf-related traits of litchi have a significant impact on litchi yield and quality. However, due to limitations such as the density of the genetic linkage map, there have been few studies on mapping QTLs of branch- and leaf-related traits. In this study, a high-density genetic map was constructed by next-generation sequencing (NGS) using an F₁ population of 264 progenies, derived from the cross between the cultivars ‘Sanyuehong’ and ‘Ziniangxi’. A total of 2574 high-quality BINs (binomial intervals) were obtained, and a genetic linkage map was constructed with a total length of 1753.3 cM and an average marker distance of 0.68 cM. With the genetic map and the phenotyping of single leaf length (SLL), single leaf width (SLW), leaf shape index (LSI), weight of specific leaf (WSL), petiole length (PL) and compound leaf length (CLL) measured in three seasons, 11, 9, 9, 10, 9 and 12 QTLs were detected for SLL, SLW, WSL, LSI, PL and CLL traits, respectively. Among these QTLs, five QTLs were consistently detected in two seasons and 12 pleiotropic QTLs were identified for at least two traits. These findings will provide new insights for the gene cloning for branch- and leaf-related traits as well as marker-assisted selection (MAS).

Litchi (Litchi chinensis Sonn.) is a type of commercially prevalent subtropical and tropical fruit. Since litchi has a highly heterozygous genetic background and a long reproductive cycle, conventional breeding methods (such as hybridization) have limited ability to nurture new litchi cultivars. Here, an efficient and stable Agrobacterium tumefaciens-mediated genetic transformation of embryogenic callus was established in ‘Feizixiao’ litchi. Transgenic materials were verified using polymerase chain reaction (PCR) analysis, β-glucuronidase (GUS) assay, and green fluorescent protein (GFP) assay. To implement the technology of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/associated protein 9 (CRISPR/Cas9) technology in ‘Feizixiao’ litchi and verify the validity of these transformation systems, the litchi polyphenol oxidase gene (LcPPO, JF926153) was knocked out. Various categories of mutations, covering base insertions, deletions, and substitutions, were found in transgenic materials via sequence analysis. The transformation system achieved high feasibility and efficiency, and the system of CRISPR/Cas9 was successfully employed to edit genes in ‘Feizixiao’ litchi. This work provides an essential foundation for investigating the functions of genes and accelerating litchi genetic improvement.