Construction of a high-density genetic map and QTL mapping of growth traits in kiwifruit

• A high-density genetic map was constructed in a diploid kiwifruit F1 population. • Eight QTLs related to the growth vigor of kiwifruit were identified. • SNP markers related to trunk diameter and annual branch diameter were developed. The trunk diameter (TD) and annual branch diameter (ABD) are closely associated with the growth vigor, abiotic resistance and fruit yield of kiwifruit. These traits are quantitative traits that are controlled by more than one quantitative trait loci (QTLs). However, QTLs for TD and ABD in kiwifruit remain unelucidated. In this study, we generated a cross of the diploid species Actinidia chinensis ‘Hongyang’ (♀) × ‘Boshanbiyu’ (♂) and performed restriction-site associated DNA sequencing on the parents and 173 F1 progeny to identify single-nucleotide polymorphisms (SNPs) in the population. A high-density linkage map spanning 2,548.97 cM was developed using 6,506 bin markers. This bin map consisted of 29 linkage group (LG), with an average genetic distance of 0.39 cM. A total of 8 QTLs were identified: four for TD and four for ABD, with the variance explained by these QTLs ranging from 4.43 % to 16.11 %. A total of 358 TD genes and 181 ABD genes were extracted from the mapped QTLs, and analyzed by KEGG enrichment. In addition, we developed a TD marker from LG23 and an ABD marker from LG10 which were significantly correlated with growth traits. The TD marker is associated with Actinidia22292, a gene involved in protein polar localization, while the ABD marker is linked to Actinidia40478, an Ein3-binding F-box protein. The two SNP markers developed in this study were further validated in a biparental population, indicating their potential use in predicting seedling growth vigor. In summary, these genetic findings deepen our understanding of the genetic basis of growth traits in kiwifruit, and provide valuable information to facilitate kiwifruit breeding.