Tree Genetics and Molecular Breeding 2024, Vol.14, No.6, 269-276 http://genbreedpublisher.com/index.php/tgmb 270 2 Key Traits of Kiwifruit and Their Genetic Basis 2.1 Overview of key traits in kiwifruit Kiwifruit, belonging to the genus Actinidia, is valued for several key traits including yield, fruit quality, and disease resistance. Yield is influenced by factors such as flowering duration and fruit weight, which have shown high heritability, indicating potential for genetic improvement through selection. Fruit quality is characterized by attributes like vitamin C content, soluble solids, and fruit weight, with significant genetic variation observed among different kiwifruit germplasms. Disease resistance, although less frequently highlighted, is crucial for maintaining healthy crops and ensuring consistent yield and quality (Scaglione et al., 2015). 2.2 Advances in kiwifruit genomics and the identification of regulatory genes Recent advances in kiwifruit genomics have significantly enhanced our understanding of its genetic makeup. The draft genome of Actinidia chinensis has been sequenced, revealing important insights into its genetic structure, including ancient hexaploidization and recent whole-genome duplication events that have contributed to the diversification of genes regulating key traits like vitamin C and flavonoid metabolism (Liao et al., 2019). Genome-wide association studies (GWAS) have identified SNP markers associated with important traits, facilitating molecular breeding efforts4. Additionally, transcriptome analyses have identified key genes involved in anthocyanin biosynthesis, which are crucial for fruit coloration (Figure 1) (Liao et al., 2021a). Figure 1 Analysis of key regulatory genes for key metabolites in kiwifruit (Adopted from Liao et al., 2021a) Image caption: Test materials (A) ‘Ganlv 1’ and ‘Ganlv 2’ had similar botanical traits and flowering stages; (B) Simple sequence repetition (SSR) technology was used for genetic similarity coefficient analysis, and the genetic similarity coefficient value of test materials was less than 0.08, the bar at the bottom is the bar of genetic similarity coefficient, the solid circle represents the female germplasm, the hollow circle represents the male germplasm, and ‘Ganlv 2’ was marked in red; (C) Fruit developmental stages and sampling time points of ‘Ganlv 2’ and ‘Ganlv 1’, the early mature germplasm ‘Ganlv 2’ had reached the commercial harvested standard at S7 (Adopted from Liao et al., 2021a) 2.3 Impact of genomic complexity on genetic improvement of kiwifruit The genomic complexity of kiwifruit, characterized by polyploidy and extensive genetic diversity, presents both challenges and opportunities for genetic improvement. The presence of multiple whole-genome duplication events complicates the genetic landscape, making it challenging to pinpoint specific genes responsible for desirable traits (Liao et al., 2021b). However, this complexity also provides a rich genetic resource for breeding programs, allowing for the incorporation of diverse traits through techniques like marker-assisted selection and interspecific hybridization. The development of linkage maps and identification of sex-determining chromosomes further aid in the efficient selection and breeding of kiwifruit varieties (Lee et al., 2020).
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