| The propagation of potato by in vitro culture of axillary buds is not only used in the production of disease-free seed tuber, germplasm exchange and conservation, but also is a suitable experimental system to study the tuber formation and carbohydrate metabolism. The microtuber is also a good material to be used in genetic transformation. This research was carried out to determine the effect of various factors on microtuber formation and development on the base of the micropropagation system established. In addition, the effects of salt stress on plantlet and microtuber in vitro were also investigated. The main results were as follows:1. The results of comparing 3 microtuber inducing systems showed that the liquid system has more microtuber number and weight, lower cost due to the exclusion of agar. It was still the main approach to produce microtubers. The liquid + solid system also has higher yield and still has the potential for further improvement. The solid system was to produce microtubers by the node directly, which is not only helpful to reduce the induction period and obtain more uniform microtubers, but also make researchers easier to estimate the development stage. Therefore, it was a suitable tool to study the tuber formation, and the liquid + solid and solid systems were mainly used in this study.2. The information and yield of microtubers were affected by photoperiod and temperature. The result showed that lower temperature (17℃) was more suitable for the microtuber information while 25℃, higher temperature (25℃) was helpful for the development of inducedformed microtubers. The highest yield was got obtained in darkness for genotype Kexin-1 and in 8h photoperiod for Helanwuhua. The chlorophyll content of microtubers was affected mainly by photoperiod, and itwhich was increased with the increasing of photoperiod. Chlorophyll b content was more than chlorophyll a on in the same condition of photoperiod and temperature, and total chlorophyll content for each every cultivar was higher at 17℃ than 25℃3. The formation and yield of microtubers were affected by nutrient composition in culture medium. The result showed that increasing of KH2PO4, CaCl2-2H2O and decreasing of MgSO4-7 H2O can significantly promote microtuber number, diameter and fresh weight. In all microelements, Mn and Fe were more important than B on the microtuber production, and Cu and Zn had no significant effect. The best treatment was MnSO4-4H2O (25.35 mg/L), FeSO4-7 H2O (55.6 mg/L), H3BO3(6.2 mg/L), CuSO4-5H2O (0.0125 mg/L), ZnSO4-7H2O(4.3 mg/L).4. Plantlet growth and microtuber development can be controlled by plant growth regulators. The result showed that: 1). The shoot length of potato explants increased with the increasing of IAA concentrations (0.5-10 mg/L) in all hormonal treatments especially with the addition of GA3 (0.5 mg/L), but inhibited by BAP (5 mg/L). The root number and root fresh weight of potato explants increased with the increasing of IAA levelseither in the presence of GA (treatment IAA+GA) or not (IAA alone). However, no any root was observed in the treatment IAA+BAP, instead there were brown swollen calli formed around the lower cut surface of the explants. The addition of GA remarkably increased the fresh weight and diameter of such calli. Microtubers were formed in the treatments of IAA + BAP and IAA + GA + BAP, but were not observed in the treatments of IAA alone or IAA + GA. Higher IAA concentrations (2.5-10 mg/L) were helpful to form sessile tubers. With the increasing of IAA levels, the fresh weight and diameter of microtubers increased progressively. At 10 mg/L IAA, the fresh weight and diameter of microtubers in the treatment of IAA + GA + BAP were 409.6% and 184.4% of that in the treatment of IAA + BAP respectively, suggesting the interaction effect of GA and IAA in potato microtuberization. 2). Growth of potato explants was inhibited completely by the application of 0.1-1 mg/L paclobutrazol in the MS propagation medium. The growth of stems and leaves was inhibited, but leaf c...
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