Study on tissue culture and rapid propagation of Xiaoguo Tianshi as a sweet persimmon rootstock

Abstract：【Objective】Persimmon (Diospyros kaki Thunb.) belongs to the genus (Diospyros Linn.) of the family Ebenaceae. China is rich in persimmon germplasm resources and one of the persimmon-producing countries with the longest cultivation history, the largest cultivated area and the largest yield in the world. Persimmon fruit tastes delicious, with unique flavor and high nutritional, and medicinal value, and is favored by consumers. At present, persimmon is often divided into sweet and astringent persimmon types according to whether the fruit can be deastringent naturally on the tree after maturity. Sweet persimmon can be crisp after ripening without any artificial treatment, sweet and refreshing, and the fresh experience of goods is excellent. The convenient transportation results in a higher economic value and persimmon industry at home and abroad focus on the development of varieties. At present, the lack of suitable rootstock in the sweet persimmon growing is the main reason that restricts its large scale development. Many domestic scholars have concluded that Xiaoguo Tianshi is a widely compatible and preferred rootstock for sweet persimmon. If the conventional seed and seedling breeding method is applied, the offspring traits will separate, and in this way, seedling breeding cycle is limited, and the yield is insufficient, so that it is difficult to meet the continuous growing market demand. Therefore, it is very important to use plant tissue culture technology for rapid propagation of Xiaoguo Tianshi as high-quality rootstock seedlings. Therefore, tissue culture has made great progress in persimmon cropsand has been widely used in persimmon varieties and rootstock seedling breeding. However, there are few reports on tissue culture of Xiaoguo Tianshi, and because of the differences in physiological characteristics, explants, culture methods and other aspects among different persimmon crop varieties, the tissue culture and rapid propagation technology system of other persimmon varieties cannot be effectively applied. Therefore, the establishment of Xiaoguo Tianshi tissue culture and rapid propagation technology system is of great significance to realize the factory production of Xiaoguo Tianshi tissue culture seedlings.【Methods】First of all, the materials were collected in different months and different disinfection methods were used to disinfect the surface of the stem segments of the current year’s young shoots, which were inoculated on the different start-up medium, and the contamination rate, browning rate and survival rate of explants were calculated. Secondly, the sterile bud obtained from the start-up medium was inoculated on different subculture media, and the subculture multiplication coefficient and the growth of the plantlets were counted. Finally, the sterile single bud with strong growth vigor, stem and leaf spreading and height of 3-4 cm was selected to inoculate on different rooting media, and the rooting rate, root number and root length were calculated. Through these methods, the best explants were selected, such as the time of material collection, sterilization method, start-up medium, subculture medium and rooting medium. The effects of time, sterilization method and proportion of plant growth regulators on explants disinfection, start-up culture, subculture and rooting culture were studied.【Results】In different months of the year, the suitable time for Xiaoguo Tianshi explant sampling was in April and June. The explants were sterilized in 75% alcohol and 0.1% HgCl2 for 10 s and 8 min, the explants of Xiaoguo Tianshi had the lowest contamination rate and browning rate, and the survival rate reached to 76.67%. The medium for the initial culture was (1/2N) MS+2.5 mg · L^-1 ZT +0.1 mg · L^-1 NAA+30 g·L^-1 sucrose and 4.5 g·L^-1 agar, the new buds grew well, the buds were robust and vigorous, and the percentage of axillary buds was up to 78.33%. The medium for the subculture was (1/2N) MS+ 2.0 mg·L^-1 ZT +0.1 mg·L^-1 NAA+30 g·L^-1 sucrose and 4.5 g·L^-1 agar, the subgeneration seedlings grew well, the leaves stretched fully, the plants were strong and vigorous, and the multiplication coefficient reached to 1.77. The rooting medium was 1/2MS+1.0 mg·L^-1 IBA+30 g·L^-1 sucrose and 4.5 g·L^-1 agar, with a rooting rate of 74.73%, the average root number was 3.33, and the average root length was 2.60 cm. 【Conclusion】The production efficiency of Xiaoguo Tianshi seedlings could be effectively improved by plant tissue culture. Therefore, in this study, the key technological processes were confirmed, including explant disinfection, start-up culture, subculture and rooting culture in tissue culture by using the stem segment of Xiaoguo Tianshi with buds as explants, and the results can provide a reference for the industrial production of tissue culture plantlets of Xiaoguo Tianshi.