Advances and achievements on Chinese jujube breeding in China

Chinese jujube (Ziziphus jujuba Mill.), an important fruit tree species native to China, has a cultivation and utilization history of more than 7,000 years. It is distributed throughout China now with a very high diversity of germplasms which provides a wide background for breeding. In this paper, the breeding objectives, techniques and achievements in Chinese jujube were reviewed and summarized. The breeding objectives on Chinese jujube changed with the development of economy and the improvement of people's living standards from focusing on high yield and big fruit to good quality, high nutrition, easy-management and high resistance to fruit shrinking and cracking. Nowadays, Chinese jujube breeding practice includes systematic selection, cross breeding, polyploid breeding and transgenic breeding. Selection from bud mutation, local rare germplasms and seedlings, is still a main way to obtain new cultivars in Chinese jujube. Cross breeding of Chinese jujube is very difficult owning to its small flower, cleistogamy phenomenon as well as high rate of embryo abortion. In view of the above obstacles limiting cross breeding, we first carried out researches on special germplasms screening. We found a number of germplasms suitable for parents, such as male sterile, self-fruitless or self-sterile germplasms, and those rich in cyclic nucleotides, saponins, flavones, triterpenic acids, water soluble polysaccharides, vitamin C, or resistant to fruit cracking or shrinking etc. Thereafter, techniques of controlled hybridization, embryo rescue and marker assisted selection were explored to increase the hybridization efficiency and improved in cross breeding. Polyploid breeding were even better practiced and a number of pure polyploids were acquired by combining colchicine application with in vivo bud regeneration technique. An obvious progress has been made in transgenic breeding recently. Some new excellent cultivars for table and dehydration were also briefly induced in the paper.