Propagation of of Yuluxiang pear (Pyrus bretschneideri Rehd.) through tissue culture

[Objective] Yuluxiang (Pyrus bretschneideri Rehd.) is an excellent mid-late repening variety with thin skin, delicate flesh, sweet taste aroma, and other excellent characteristics, which is widely recognized by the domestic and foreign fruit markets. In view of the large differences in tissue culture propagation among pear varieties and there was no rapid propagation system through tissue culture for Yuluxiang pear, the study aimed to establish the tissue culture technology for Yuluxiang pear, and provide technical support for further molecular biology research and production of virus-free nursery trees of Yuluxiang pear. [Methods] The experimental materials were prepared as follows: firstly, the new shoots of Yuluxiang pear were collected from the specimen garden of Hebei Agricultural University 5-10 days after flowering. Secondly, the blades of the leaves were removed, and only the petioles were kept on the stem. The single bud stem segments were cut in about 1 cm with pruning scissors and placed in a clean triangular bottle. They were rinsed with running water for 30 min, sterilized with 0.1%HgCl2 for 6 min, then sterilized with 75% alcohol for 1 min. After three times of rinsing with sterile water, they were dried using sterile filter paper. The explants were inoculated on the medium MS, with 1.00 mg·L-1 6-BA, 0.10 mg·L-1 IBA, 30.0 g·L-1 sucrose, 6.0 g·L-1 agar, and 2.0 g·L-1 PVA. Factors affecting proliferation and rooting, such as basic medium and plant growth regulator, were screened by completely randomized experiment design; the way of gradient for dark culture time and activated carbon concentration were used to optimize rooting conditions. [Results] The medium of MS+1.00 mg·L-1 6-BA+0.10 mg·L-1 NAA+30.0 g·L-1 sucrose+6.0 g·L-1 agar was suitable for the proliferation of Yuluxiang pear, and the propagation coefficient was 3.57 and the number of effective shoots was 1.17. The suitable medium for rooting of Yuluxiang pear was 1/2MS+2.0 mg·L-1 NAA+20.0 g·L-1 sucrose+6.0 g·L-1 agar. The rooting rate was 60.00%, and the average number of roots was 3.40. There was no significant difference in rooting rate and average number of roots between dark culture of 0 day, 5 days, and 15 days. The rooting rate and average number of roots of the treatments with 10 days and 20 days dark culture was significantly lower than that of the treatments with 0 day on the rooting rate and average rooting number. With the increase of dark culture time, the root became thinner, the stem tip dieback rate of the explants significantly increased, and the root callus became larger. Therefore, the dark culture had no promotion effect on rooting.0.5 g·L-1 activated carbon could promote the aboveground growth of Yuluxiang shoots. However, when the concentration of activated carbon was increased to 1.0-4.0 g·L-1, there was an obvious inhibitory effect on the aboveground parts, and the leaves of some plantlets turned brown. After 40 days culture after rooting, 132 Yuluxiang tissue culture seedlings were domesticated in the greenhouse for 10 days and transplanted into the nutrient pots. It was observed that Yuluxiang exhibited a mortality phenomenon 10 days after transplantation. The survival rate of Yuluxiang plantlets was 32.57% 60 days after transplantation, and the overall growth of the plants was robust and healthy. [Conclusion] This study screened out the optimal media for proliferation and rooting of Yuluxiang pear in vitro, successful acclimation and transplantation process for plantlets in glasshouse.