Research and utilization progress in banana germplasm resources in China

Abstract：Banana is one of the main fruit crops and important food crops in the world, and it is also an important economic fruit in southern China. China is the border area of the origin of modern bananas, and one of the secondary origin centers as well. China has a history of banana cultivation for more than 2000 years and is the second largest country in banana production and consumption. Banana producing areas in China are mainly concentrated in Guangdong, Guangxi, Hainan, Yunnan, Fujian and Taiwan, with a small amount of cultivation in the south of Sichuan, Guizhou and Tibet. Most cultivated bananas are evolved from two wild species, Musa acuminate and Musa balbisiana, and their interspecific hybridization. The genome of Musa acuminata is called“genome A”, while the genome of Musa balbisiana is called“genome B”. According to the classification value of characteristics, banana cultivars can be divided into genotypes such as AA, AAA, AB, AAB, ABB, AAAA, AAAB, AABB, BB and BBB. Bananas cultivated in China are simply divided into four categories: Cavendish (AAA), Pisang Awak (ABB), Silk (AAB) and Dajiao (ABB). Cavendish banana is planted mostly in China (more than 80% ), followed by Pisang Awak (more than 10% ). Notably, in China, few people plant and consume Plantain (AAB), which is an important staple food in some area. Banana breeding mainly includes introduction (like Brazil and Williams banana), vegetative line selection (like GCTCV bananas), artificial mutation breeding (like Jiali banana), cross breeding (like Fenza No. 1 and Zhongjiao No. 9 banana), chromosome ploidy breeding, transgenic breeding and gene editing breeding. The introduction method is sim-ple and direct. Our group took the lead in establishing the National Banana Germplasm Resource Garden in 1989. In the future, we should introduce not only high-quality varieties, but also multifunctional and diverse banana varieties to enrich China’s banana market. After introduction, people often get better lines that adapt to Chinese geographical and climatic conditions and planting habits, and then popularize them. Mutation breeding is easy, but the ideal excellent lines can only be obtained through a large number of screening and evaluation. The female flowers of some bananas, like Dajiao and Pisang Awak, have strong fertility, so they are often used as female parents to cross with wild bananas or cultivated varieties with certain fertility. Although sexual hybridization of banana needs a long period and is easy to fail, this method can often create new germplasm with diverse genetic background and relatively controllable traits, which is the most potential and promising method in traditional banana breeding at present. In recent years, researchers in China have created many new hybrid banana germplasm, and it can be predicted that a large number of new hybrid banana varieties will emerge in China in the near future. Banana transgenic and gene editing breeding have strong pertinence. China has made good achievements in the fields of banana transgenic and gene editing. However, as in many other parts of the world, these methods cannot be applied to business at present. At last, other breeding methods like somatic hybridization, rapid breeding and molecular- assisted breeding are rarely used at present. Banana Fusarium wilt and other diseases seriously threaten banana industry in China. At the same time, frequent typhoons and floods, severe frost and poor soil in the main banana producing areas in China also limit the further development of banana industry. Breeding new banana varieties with high yield, high quality and high stress resistance and adaptability is the key to break the bottleneck of banana industry development in China, and it is also a challenge for banana breeders in China. In addition, it is also an important direction to cultivate bananas with high nutrition and health care function, which are suitable for industrial processing or feed. During the last decades, China has made great achievements in banana breeding, but there are still many problems. First of all, banana biodiversity is relatively lacking, with few wild banana resources. Moreover, the careful evaluation of banana germplasm resources is not enough, limiting the utilization of them. Secondly, the main banana varieties in China were bred by introduction and mutation breeding, and only a few were bred by hybridization or other means. Moreover, due to many reasons, there is a lack of varieties with good comprehensive characteristics. Finally, it is difficult to study genes in banana through the forward or reverse genetic means, limiting the molecular research on banana. In the future, we should: (1) Continue to strengthen the collection, evaluation and utilization of global banana germplasm resources, and especially promote banana cross breeding vigorously; (2) Pay attention to the basic research on banana, dig out the key genes related to important economic traits, and analyze their regulatory networks, so as to lay the foundation for creating new banana varieties without transgene through gene editing technology in the future; (3) Continuously develop and upgrade new breeding techniques, promote the integration of various means, and breed efficiently and scientificly; (4) Breed new varieties that are resistant to various diseases and have good comprehensive properties, so as to win the banana defense war. In a word, we have summarized the research results of banana breeding in China in recent years, discussed the methods of banana breeding, the direction of new variety breeding and the main problems, in order to provide reference for banana breeding in China.