Abstract:【Objective】‘Yuluxiang’ (Pyrus bretschneideri Rehd.) is an excellent mid-late maturing 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 tissue culture system for ‘Yuluxiang’ pear, this paper carried out relevant research, aiming to establish the tissue culture technology system for ‘Yuluxiang’ pear, and provide technical support for further molecular biology research and virus-free seedlings cultivation of ‘Yuluxiang’ pear.【Methods】We obtained the experimental materials as follows: firstly, the new shoot explant of ‘Yuluxiang’ pear was collected from the specimen garden of Hebei Agricultural University after flowering 5~10 days. Secondly, the leaves of the explants were removed, leaving only the petiole. The single bud stem segment was cut to about 1 cm with pruning scissors and placed in a clean triangular bottle. It was rinsed with running water for 30 min, sterilized with 0.1% HgCl2 for 6 min, then with 75% alcohol for 1 min. After rinsed three times with sterile water, it was dried using sterile filter paper. The explant was 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, and expanded to a certain amount to carry out the experiment. 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 was used to optimize rooting conditions.【Results】After compared the effect of basic medium (MS, 1/2MS, 1/4MS, NN69, WPM) and plant growth regulators (6-BA, NAA and IBA) on proliferation, it was found that 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 the suitable medium for the proliferation of ‘Yuluxiang’ pear, and the propagation coefficient was 3.57 and the number of effective seedlings was 1.17. The effects of basic medium (MS, 1/2MS, 1/4MS, NN69, 1/2NN69, 1/4NN69) and plant growth regulators (NAA or IBA) were compared on rooting effect of tissue culture seedlings. The suitable rooting medium for ‘Yuluxiang’ pear was 1/2MS+2.0 mg·L-1 NAA +20.0 g·L-1 sucrose +6.0 g·L-1 agar. Under this rooting medium, the rooting rate was 60.00%, and the average number of rooting strips was 3.40. Based on the selected rooting medium, other culture factors affecting rooting were compared and the results were as follows. Compared the effect of dark culture for 0, 5, 10, 15, 20 days on rooting efficiency, there was no significant difference on rooting rate and average rooting number between dark culture for 5 days, 15 days and 0 day. The treatment of dark culture for 10 days and 20 days was significantly lower than the 0 day on the rooting rate and average rooting number. Compared to other treatments, the root of dark culture for 0 day was more robust. With the increase of dark culture time, the root became thinner, the stem tip dieback rate of tissue culture seedlings significantly increased, and the root callus became larger. After dark cultured for 20 days, all the stem tips died and the callus reached the maximum, which had significant inhibition effect on rooting and the ground part. In sum, dark culture had no significant promotion effect on rooting. We also compared the effect of activated carbon of 0~4.0 g·L-1 added to the medium on rooting. It was found that when the activated carbon was added to the medium 0.5~4.0 g·L-1, the rooting number was significantly decreased compared with the control (without activated carbon). When activated carbon was 1.0~4.0 g·L-1, the rooting rate and rooting number were 0. When the concentration of activated carbon was 0.5 g·L-1, it could promote the aboveground growth of ‘Yuluxiang’ seedlings. 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 seedlings turned brown. To sum up, the addition of activated carbon significantly inhibited the rooting of ‘Yuluxiang’ pear. After 40 days of induced 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. This situation stabilized after 60 days, at this time, the survival rate of ‘Yuluxiang’ was 32.57%, and the overall growth of the plant was robust and healthy.【Conclusion】This study identified the optimal medium for proliferation and rooting, ensured the suitable rooting conditions for ‘Yuluxiang’ pear, and established a successful acclimation and transplantation process for tissue-cultured seedlings. In conclusion, the rapid propagation system for ‘Yuluxiang’ pear had been established.
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