Studies On The Potato Quality Formation And Regulation Using Microtuber-inducing System

Formation of potato microtubers in vitro is a suitable experimental system to study the tuber formation and carbohydrate metabolism. Based on the micropropagation system established, this research was carried out to determine the effect of various environmental conditions, such as photoperiod and temperature, nutrient, irradiation and salt stress on microtuber development, yields and quality. In addition, the effects of storage temperature and period on the changes of quality and physiological characters in tubers were also investigated and discussed. The main results were as follows:1. The yield and quality of microtubers were affected by photoperiod and temperature. The result showed that lower temperature (17 ℃) was more suitable for the microtuber information while higher temperature (25℃) was helpful for the development of formed microtubers. The highest yield was obtained in darkness for cultivar Kexin-1 and in 8h-photoperiod for Helanwuhua. The chlorophyll content of microtubers was affected mainly by photoperiod, which was increased with the increasing of photoperiod. Chlorophyll b content was higher than chlorophyll a at the same photoperiod and temperature. The content of TGA increased with the increasing of photoperiod and showed very significant (positive) relationship with chlorophyll content. Longer photoperiod was helpful for the accumulating of dry matter, starch and sugar in tubers, and they were higher at 25℃ than at 17 ℃. While Vc content also increased with increasing of photoperiod but it was higher at 17 ℃ than at 25 ℃.2. Microtuber yield and qulity could be controlled by plant hormones and growth regulators. The result showed that: 1) GA improved stem and leaf growth and stolon elongation of microplantlets, but inhibited or prolonged microtuber formation and decreased markedly the production; 2) CCC inhibited the growth of plantlets, and played a inducing role for the formation of tubers in cultivars Kexin 1 and Helanwuhua but restricted the further expantion of tubers formed. 3) Adding of JA and SA promoted the formation of microtubers, and improved their yields significantly. 4) GA inhibited the starch synthesis and increased the reducing sugar content which was not helpful for the process. CCC, JA and SA treatments not only increased the starch contents of 2 cultivars in this experiment, but also increased the Vc and protein contents and decreased reducing sugar content. Therefore, all 3 growth regulators were helpful for the improvement of process quality of tubers.3. The yield and quality of microtubers were affected by nutrient compositions in culture medium. The result showed that Mn and Fe were more important, while B, Cu and Zn had no significant effect on the microtuber production and quality. The microtuber yield and quality could be improved significantly if the content of MnSO4.4H2O was doubled and that of FeSO4.7 H2O and CuSO4.5H2O were increased 0.5 folds based on the content in standard MS medium.4. Explants obtained from in vitr-propagated plantlets of two potato cultivars were treated with five doses of gamma radiation (0, 2, 4, 6 and 8 Gy) to investigate the stimulating effects of low irradiation on the production and quality of microtubers in vitro. Irradiation of the plantlets with 4 Gy radiation led to a significant increase not only in the microtuber number (116.7 % and 34.5 % increase over the control) but also in the fresh weight of two potato cultivars (77.6 % and 23.2 % increase over the control, respectively). 2 Gy radiation treatment increased the dry matter content of microtubers, 2-4 and 6-8 Gy radiations werehelpful for starch and Vc contents in tubers respectively, but increased the reducing sugar content. No significant difference for the effect of radiation treatments on protein content was observed.5. With increasing salt intensity, the microtuberization of potato was delayed 5-10 days (20 and 40 mM NaCl) or inhibited completely (80 mM NaCl), along with the reduction of microtuber yields. Salinity applied from 20 to 60 mM p...