Tree Genetics and Molecular Breeding 2025, Vol.15, No.2, 70-79 http://genbreedpublisher.com/index.php/tgmb 71 The traditional breeding method is to select individuals with good growth and good traits from the natural population for reproduction. “Hayward” kiwifruit is a variety selected through natural selection. 2.2 Milestones in kiwifruit breeding history In the 1970s, New Zealand established a formal breeding program, which promoted the birth of many new varieties and introduced yellow-fleshed and red-fleshed kiwifruits that had significantly improved in appearance and flavor compared to the original green-fleshed types (Hanley, 2018). The development of in vitro culture technology has made the breeding of kiwifruit more efficient. Wu’s research in 2018 found that the combination with polyploid breeding methods enriched the variety types and improved the overall quality of the fruits. The linkage maps established by RAD technology have helped breeders identify genetic markers related to the target traits and made mark-assisted selection (MAS) more accurate and reliable (Scaglione et al., 2015). 2.3 Transition from conventional to modern breeding techniques The genome of kiwifruit has been sequenced, and the cost of genotyping is now much lower than before. Hanley (2018) found that techniques such as MAS and genomic selection (GS) have begun to be used in actual breeding, which is beneficial for breeders to find plants with ideal traits more quickly and also accelerates the selection and breeding of new varieties. Varkonyi-Gasic et al. (2018) edited the gene CENTRORADIALIS-like through CRISPR/Cas9, enabling kiwifruit to flower earlier and become a compact plant type, which made breeding faster and cultivation more convenient. Zhao et al. (2022) demonstrated that molecular cellular genetic techniques such as FISH and GISH have now also been optimized. These techniques are useful for a clearer understanding of the genetic structure and evolutionary relationships of kiwifruit, as well as for improving the accuracy and efficiency of breeding. 3 Genetic Diversity and Parent Selection 3.1 Overview of genetic diversity in kiwifruit Kiwifruit belongs to the Actinidiaceae family. The A. chinensis complex has rich genetic diversity, and these genetic differences are crucial for resource conservation and the long-term development of kiwifruit. When Hu et al. conducted an analysis using SSR in 2022, they discovered a large number of genetic variations, identified 888 alleles, and the expected heterozygosity was as high as 0.846. However, the actual measured heterozygosity was only 0.622, indicating that there was inbreeding among the materials. Liao et al. (2019)’s study on wild kiwifruit (A. eriantha) also found that it has significant variations in fruit traits. The obvious linkage disequilibrium found at some SSR loci indicates that these traits are related to specific gene regions. 3.2 Criteria for selecting parent plants The parents should have a relatively high genetic diversity for the offspring to be more likely to develop the desired good traits. Liao et al. (2019) and Hu et al. (2022) used molecular markers such as SSR to determine which plants had more abundant genes. The internal traits of fruits such as sugar content, carotenoids and chlorophyll can affect the sweetness, color and nutrition of the fruits. Liao et al. (2019) found that materials with good fruit quality in wild species were often selected as parents. Whether the pollen germination rate is high or not and whether it is compatible with the female parents are very important when selecting male parents. Iliescu et al. (2022) identified male materials with a pollen germination rate exceeding 90%, which performed better during pollination and were highly suitable for use as the male parent. Hanley (2018) indicated that in order to make the newly bred varieties more stable and disease-resistant, the breeding program would select disease-resistant materials from parents of different sources for use. 3.3 Role of wild relatives and existing cultivars Wild kiwifruits such as A. eriantha bring rich genetic resources and have many special traits that can be used in breeding. Liao et al. (2019) argued that wild materials have good fruit quality and significant genetic differences, and are of great value for developing new varieties. The kiwifruit varieties that have been promoted in the market have stable traits, good fruit shape, taste or yield, and are also relatively recognized by consumers. In breeding practice, these two types of materials are usually combined. Wild species provide new traits, while cultivated
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