Screening Of Salt Tolerant Diploid Potatoes And Their Physiological Characters

The threat of soil salinity to agricultural production has become a global problem, which seriously affects crop growth and yield. At present, potato has become one of the world's major food crops, ranking the fourth in production only after wheat, maize and rice. Potato is a moderately salt-sensitive crop, and soil salinity causes seriously harm to the production of potatoes. Breeding salt-tolerant potatoes is the most simple and effective way to solve the problem of soil salinization. However, potato varieties being widely used are less salt-tolerance, and this makes great restriction to breeding work. So it is in urgent need to screen germplasm for salt tolerance and study their physiological response to salt stress in a potato breeding effort aimed at the development of salt tolerant potato varieties.In this research, long-day adapted diploid Solanum phureja (PHU)– S. stenotomum (STN) hybrid clones were screened in vitro for salt (NaCI) tolerance, using tetraploid varieties, Bintje (tolerant) and Mainchipe (susceptible), as controls, and three groups of five salt tolerant, five salt susceptible and five mid-salt tolerant clones were set up based on their performance of shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, and root dry weight. Salt-tolerant physiological indicators were found by determinating physiological indices of potato plantlets in vitro at the different levels of NaCI or different treatment periods. Data were expressed in relative values prior to statistical analysis. Cell ultrastructure observation under salt stress was made to find salt-tolerant cellular indicators. Use of RAPD technology was to verify the results of salt-tolerance screening. These results could provide the material foundation and theoretical basis for screening salt-tolerant potato resources and developing new varieties of salt-tolerant potato. The main results are as follows:1. Forty five diploid clones and two tetraploid controls were partitioned into two groups by cluster analysis based on performance of the six growth parameters, shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, and root dry weight. Five diploid clones, higher in salt tolerance than Bintje, 472-1, 267-1, 89-2-1, 188-1 and 566-1, five diploid clones, more sensitive to salt stress than Mainechip, 354-1, 507-1, 270-2, 9-3 and 138-1, and five diploid inbetween, 592-3, 412-1, 474-1, 292-1 and 301-1, were selected out based on cluster analysis combined with mean value comparison.2. Main results after physiological index measurement:(1) With increase in stressed period and NaCI level, the relative value of water content in these diploid potatoes tended to increase, with salt tolerant diploid potatoes being increased less compared with salt sensitive diploid potatoes. The three groups, stressed at 40 and 60 days, or at 20 and 30 mmol·L-1 NaCI, showed highly significant difference.(2) With increase in stressed period and NaCI level, relative value of total Chlorophyll content and Chlorophyll a content tended to decrease, but the relative value of Chlorophyll b content showed no regular pattern in the. The reduced range of the salt tolerant clones was less than that of the salt sensitive clones, and there were highly significant difference between the three groups. Therefore, Chlorophyll content can be used as the index of salt tolerance in diploid potatoes.(3) With increase in the days of salt stress, SOD activity were increased at first and then decreased. The reduced range of the salt tolerant clones was less than that of the salt sensitive clones, and there were highly significant differences between the three groups. With salt concentration increased, SOD activity of the salt tolerant clones was increased, while POD activity of the salt sensitive clones was reduced. The reduced range of the salt tolerant clones was less than that of the salt sensitive clones, and there were highly significant differences between the three groups. The SOD activity of the microtuber was increased after salt stress, and the increased range of the salt tolerant clones was higher than that of the salt sensitive clones. However the POD activity of the microtuber was reduced after salt stress, and the reduced range of the salt tolerant clones was less than that of the salt sensitive clones. There were highly significant differences between the three groups for SOD and POD. Therefore, the activity of SOD and POD can be used as the index of salt tolerance in diploid potatoes.(4) With the days of salt stress and salt concentration increased, the relative conductivity and relative content of MDA in the plantlets in vitro were increased. The two parameters showed the same trend in microtuber of diploid potatoes after salt stress. However, the increased range of the salt tolerant clones was less than that of the salt sensitive clones. Therefore, the relative conductivity and relative content of MDA can be used as the indices of salt tolerance in selection for salt tolerant diploid potatoes.(5) With the days of salt stress increased, the relative value of proline content was increased at first and then decreased, and the increased range of the salt tolerant clones was higher than that of the salt sensitive clones. The relative value of soluble sugar content was increased in the salt tolerant group and decreased in the salt sensitive group. There were highly significant differences in between the three groups. With the concentration of salt stress increased, the relative value of proline content and soluble sugar content were increased, and the increased range of the salt tolerant clones was higher than that of the salt sensitive clones. The proline content was highly significantly different between the groups, and soluble sugar content of diploid potatoes under stress of 10 and 30 mmol·L-1 NaCI was highly significantly different between the groups. The proline content and soluble sugar content of the microtuber were increased after salt stress. The increases in the salt tolerant clones were higher than those of the salt sensitive clones, and there were highly significant differences between the groups. Therefore, proline content can be used as the physiological index of salt tolerance in diploid potatoes.(6) With the days and the concentration of salt stress increased, the relative value of soluble protein content in plantlets in vitro was decreased, but the change was small in both the salt tolerant and the salt sensitive clones. The soluble protein content of microtuber was decreased after salt stress. There were highly significant differences between the groups.(7) The microtuber diameter, number, the largest sized tuber weight and microtuber yield were all decreased after salt stress. It was showed that the formation and growth of the microtuber could be seriously inhibited by NaCl. The decreased range of the salt sensitive clones was higher than that of the salt tolerant clones, and there were highly significant differences between the groups.(8) The microtuber yield was highly significantly positively correlated to the microtuber diameter, tuber number, the largest sized tuber weight, the activities of SOD and POD, proline content, soluble sugar content and soluble protein content of the microtuber, while highly significantly negatively to relative conductivity and malondialdehyde (MAD) content.3. The plasma membrane, chloroplast, mitochondria and grana were all changed through the ultrastructure observed of plantlet leaves after salt stress. The destructions of the salt tolerant clones were smaller than those of the salt sensitive clones. Therefore, the plasma membrane, chloroplast, mitochondria and grana could be used as the cytology index of salt tolerance evaluation.4. The fifteen diploid clones when under stress of 10, 20, 30 mmol ? L-1 NaHCO3 were inhibited more in terms of the shoot length, shoot fresh weight, shoot dry weight, root length, root fresh weight, and root dry weight than under stress of 10, 20, 30 mmol ? L-1 NaCl, suggesting that NaHCO3 would do more harm to diploid potato than NaCI at the same concentration. At the range of concentration tested, all the six parameters were higher in the salt tolerant group than in the salt sensitive group when stressed under NaHCO3, and highly significantly difference was found between the three groups. When stressed under 10 mmol·L-1 of NaCl and NaHCO3, the diploid potato showed significantly positive correlation for shoot length, shoot fresh weight, and shoot dry weight, suggesting that diploid potatoes resistant to salt are also resistant to alkali.5. In RAPD cluster analysis, all five clones resistant to salt were assigned to one group, while salt sensitive clones and middle salt-tolerant clones were not well separated. The results demonstrated the use of growth parameters for salt tolerance screening is similar to the use of RAPD data. By RAPD cluster analysis and principal coordinates analysis, the 15 diploid potatoes were all divided into four groups, indicating that the results using the two classification methods were consistent.