Research progress in kiwifruit breeding

Abstract: China is the origin of the majority of Actinidia germplasm resources, and our country's rich germplasm resources have nurtured the development and growth of the global kiwifruit industry. There are 25 countries worldwide that produce kiwifruit. The kiwifruit area and production in China rank first in the world, and China’s share of the world's total kiwifruit harvested area reaches a substantial highland of 69.58%, while its production constitutes 52.44% of the global total production. The cultivation of superior cultivars is the foundation for the high- quality development of the industry. However, the characteristics of kiwifruit, such as dioecism (the presence of separate male and female plants), complex ploidy (varying numbers of chromosome sets), high heterozygosity (genetic diversity), and long breeding cycles, pose significant challenges for breeders. These biological traits make the development of new cultivars a complex and time-consuming process. In addition to these inherent challenges, recent environmental issues like soil salinization and frequent flood disasters in China’s kiwifruit production areas have presented new challenges to breeders. These environmental cues can significantly impact the growth and yield of kiwifruit, making the development of stress-resistant cultivars a priority. Cultivating top-quality, high-yield and stress-resistant new cultivars is a key to breaking through the bottlenecks in the development of China’s kiwifruit industry. The industry must adapt to these challenges to ensure its continued growth and sustainability. To date, a total of 265 new cultivars have been cultivated through methods such as wild germplasm selection, seedling selection, bud mutation selection, mutation breeding and hybrid breeding. Moreover, in China, 94.6% of kiwifruit cultivation area is plantedwith the cultivars developed in China with independent intellectual property rights. Molecular marker assisted selection and other high efficiency breeding technologies have begun to be applied in kiwifruit, representing a step forward in the precision and efficiency of breeding programs. However, there has not yet been a new cultivar released that fully relies on molecular breeding technology research and development. This suggests that, while molecular techniques are still in early stage of being integrated into breeding programs, there is still room for growth and further development in this area. Currently, a total of 10 kiwifruit genomes and 11 genetic linkage maps have been published domestically and internationally. These resources are invaluable for understanding the genetic makeup of kiwifruit and for identifying the genes associated with desirable traits. They have laid the foundation for the future development of efficient breeding technologies, like marker- assisted selection and genomic selection, which can accelerate the breeding process and improve the precision of trait selection. However, there are still some issues to slow down the progress in the discovery of excellent new genes and unclear genetic mechanisms for many important agronomic traits in kiwifruit. These challenges highlight the need for continued research and investment in the genetic understanding of kiwifruit. The identification and utilization of new genes can lead to the development of cultivars with improved resistance to diseases, strong tolerance to environmental stress and enhanced fruit quality. In the future, it is necessary to further strengthen scientific research on the development and utilization of germplasm resources and the cultivation of superior male and rootstock varieties. This includes investing in the infrastructure and expertise required to conduct advanced genetic research, as well as fostering collaboration among researchers, breeders and farmers to ensure that new cultivars are not only scientifically sound but also practical for cultivation and market demands. In conclusion, the future of the kiwifruit industry in China, and even on the world, depends on a combination of continued genetic research, the application of modern breeding technologies and sustainable agricultural practices. By addressing the challenges of breeding and cultivation, and also by leveraging the rich germplasm resources of China, the industry can continue to thrive and meet the needs of a growing global market.