Establishment of a 2n pollen induction method based on minimum invasion in Chinese jujube (Ziziphus jujuba Mill.)

As a native fruit tree species in China, Chinese jujube has a cultivation history of more than 7000 years. Nowadays, it has almost 1000 cultivars most of which are diploid with somatic chromosome number of 24 (2n=2x=24). 'Zanhuangdazao' and Pingguozao' are natural triploids identified up to now, which have the valued attributes of big fruits, high yield and good adaptation. Thereby, polyploid breeding is becoming more and more attractive. Unreduced pollen has been widely used in breeding of many fruit tree species, however, it has not yet been used in Chinese jujube breeding. The reason is that jujube flowers produce less number of 2n pollen naturally and about 70% cultivars never produce 2n pollens naturally. Colchicine application can induce 2n pollen production in many plants. The application time, concentration and treating duration were tested systemically aimed to induce 2n pollen. A minimum invasive method (MIM), which combines half-cutting with colchicine treatment on the base of bearing shoots when the flower buds were at meiosis, was developed. Colchicine concentrations significantly influenced the induction of 2n pollen with ratios of 3.39, 10.71, 16.75, 3.84 and 3.82% when colchicine concentration was 0.05, 0.1, 0.3, 0.5 and 0.7%, respectively. And, colchicine treatment duration also remarkably affected the induction of 2n pollen with ratios of 16.75, 3.04 and 4.20% when the duration was 24, 36 and 48 h, respectively. The viability of 2n pollens was at the same level with that of n pollens which provided useful materials for polyploid breeding in Chinese jujube.