| Salinization has become a problem worldwide that threatens the agricultural production. Biological improvement method may utilize and improve the saline-alkaline soil by cultivating salt tolerant crops. The potato is a moderatly salt sensitive crop, and the common tetraploid (Solanum tuberosum L.) parents have narrow genetic basis, however, the diploid potato contains very valuable genes, and is an important germplasm that can widen the existing genetic base and be used for breeding the salt tolerant varieties. Therefore, in this research, the salt tolerance, alkali tolerance and QTL analysis of morphological traits under NaCl stress of the long-day adapted diploid Solanum phureja (PHU)-S. stenotomum (STN) hybrid clones (PHU-STN) were studied. The research results may have important theoretical and practical implications for salt and alkali tolerant breeding.In this research, the PHU-STN hybrid clones in vitro were used as materials to screen diploid potato clones of various levels of NaCl tolerance under NaCl stress, and understand if there is any consistency of salt sensitivity for dipoloid potatoes cultured in vitro and in pot under NaCl stress. Also, alkali tolerance of clones with various levels of NaCl tolerance was investigated under NaHCO3stress. Furthermore, the molecular genetic map of potato was constructed using SSR and AFLP molecular marker technology, and preliminary position QTL of morphological traits was conducted under NaCl stress and reliable QTL were detected, that can provide theoretical and material basis for QTL fine mapping and cloning of potato salt-tolerant gene. The main results are as follows:1. The PHU-STN hybrid population that included164diploid potato clones and their parents were sressed under80mmol·L-1NaCl, and parents were used as controls. Based on the performance of morphological traits, nineteen clones with stronger salt tolerance than the salt tolerant parent and one clone with weaker salt tolerance than the salt susceptible parent were identified. These clones will be important germplasm that could widen the existing genetic base and be used for breeding the salt tolerant varieties. The broad sense heritability of six morphological traits of the PHU-STN hybrid population were over0.9, suggesting that these traits were controlled mainly by genetic factors and affected less by the environments.2. The diploid potato clones with various levels of NaCl tolerance that included five salt tolerant clones, five moderatly salt tolerant clones,5salt susceptible clones and their parents were stressed under10,20and30mmol·L-1NaCl. On the basis of performance of physiological traits, the conclusions are as follows:1) Under10mmol·L-1NaCl stress, the chlorophyll content and relative water content of salt tolerant clones increased, while the chlorophyll content and relative water content of salt susceptible clones decreased. Under NaCl stress greater than20mmol·L-1, the chlorophyll content and relative water content of the clones with various levels of NaCl tolerance decreased.2) Under NaCl stress, the malondialdehyde (MDA) content, proline (pro) content, soluble sugar content, soluble protein content, superoxide dismutase (SOD) activity and peroxidase (POD) activity of the clones with various levels of NaCl tolerance increased, and with NaCl concentration continuing to increase, the values of all six traits tested tended to incease further.3) Under NaCl stress, the chlorophyll content, relative water content, MDA content, proline content, soluble sugar content, soluble protein content, SOD activity and POD activity of the salt tolerant clones were higher than moderatly salt tolerant clones, and the moderatly salt tolerant clones were higher than the salt susceptible clones, suggesting that the sensitivity of parents and15progeny clones to salt stress was consistent in physiological traits and morphological traits.4) The physiological traits measured were differently sensitive to salt stress, and proline, MDA, SOD and soluble sugar were more sensitive, hence, they could be used to evaluate the salt tolerance of diploid potato. Comparing the physiological traits measured between treatments and control, the difference was obvious under30mmol·L-1NaCl stress, so the concentration was suitable for evaluating the salt tolerance of diploid potato.3. In pot experiment conditions, the diploid potato clones with various levels of NaCl tolerance that included two salt tolerant clones, two moderatly salt tolerant clones, two salt susceptible clones and their parents were stressed under30and60mmol·L-1NaCl, and the performance of physiological traits showed that salt sensitivity of dipoloid potato in vitro and in pot was consistent, therefore, evaluating salt tolerance of diploid potato in vitro was feasible.4. The diploid potato clones with various levels of NaCl tolerance that included5salt tolerant clones,5moderatly salt tolerant clones,5salt susceptible clones and their parents were stressed under5and10mmol·L-1NaHCO3, and on the basis of performance of morphological and physiological traits, the conclusion are as follows:1) NaHCO3stress inhibited the growth of diploid potato clones, and the higher the NaHCO3concentration was, the stronger the inhibition was.2) Under NaHCO3stress, the chlorophyll content, soluble sugar content and SOD activity of diploid potato clones decreased, and when NaHCO3concentration was higher, the values of three traits were smaller.3) Under5mmol·L-1NaHCO3stress, the relative values of carotenoid content of salt tolerant and moderatly salt tolerant clones were greater than100, while the relative values of carotenoid content of salt susceptible clones were smaller than100; the relative values of relative water content of salt tolerant clones were greater than100, while the relative values of relative water content of moderatly salt tolerant and salt sensitive clones were smaller than100. Under10mmol·L-1NaHCO3stress, the carotenoid content and relative water content further decreased, and the relative values of clones with various levels of NaCl tolerance were all smaller than100.4) Under NaHCO3stress, the proline content, MDA content and soluble protein content of diploid potato clones increased. When NaHCO3concentration was increased, the MDA content and soluble protein content were increased, but the proline content decreased, however it is still greater than100.5) Under5mmol·L-1NaHCO3stress, the POD activity of salt tolerant clones decreased, but the POD activity of salt sensitive clones increased,.With NaHCO3increase, the POD activity of clones with various levels of NaCl tolerance was all increased.6) Under5mmol·L-1NaHCO3stress, the performance of morphological and physiological traits showed that the alkali tolerance of salt tolerant clones were stronger than moderatly salt tolerant clones, and moderatly salt tolerant clones were stronger than salt susceptible clones. Under10mmol·L-1NaHCO3stress, except shoot lengh, the performance of other traits indicated that the alkali tolerance of salt tolerant clones were stronger than moderatly salt tolerant and salt sensitive clones, but the alkali tolerance of moderatly salt tolerant and salt susceptible clones had no difference.7) Alkali stress was different from salt stress. Alkali stress inhibited the growth of diploid potato clones more than salt stress. The performance of diploid potatos under NaHCO3stress indicated that the salt-tolerant diploid potatoes were also tolerant to alkali, namely, salt tolerance and alkali tolerance had a certain correlation5. The software Joinmap4.0was used for linkage analysis on a population including94diploid potato clones, and a molecular genetic map that consisted of16main linkage groups was constructed. One hundred and forty AFLP and19SSR markers were organized into the linkage groups covering a total distance of1093cM. The average interval distance was6.87cM between markers, length of linkage group varied from10.06-138.27cM, and the average length was68.31cM. Among16linkage groups, the longest LG1was138.27cM, and the shortest LG8was10.06cM. The molecular genetic map may provide the basis for preliminary position QTL of morphological traits under NaCl stress.6. QTL IciMapping3.2software, inclusive composite interval mapping and the phenotypic data of the relative value of six morphological traits under NaCl stress were employed to detect QTL and the marker interval. Six QTLs were detected that were associated with4morphological traits under NaCl stress. Among six QTLs, qSL-1-1for shoot length explained the genetic variance of10.25%; qSDW-14-1for shoot dry weight explained the genetic variance of9.20%; qRFW-10-1, qRFW-10-2and qRFW-14-3for root fresh weight explained the genetic variance of16.79%,10.83%and10.29%, respectively; and qRDW-1-1for root dry weight explained the genetic variance of31.48%, which was possibly a major gene locus. In addition, qSDW-14-1and qRFW-14-3were located on the same position which was between EACAMCAC307.5and EACAMCAC111.54on LG14, and they closely linked with marker EACAMCAC307.5. It showed that a major gene locus or several closely linked genes existed in the interval and the gene locus simultaneously controlled shoot dry weight and root fresh weight under NaCl stress. Six QTLs detected that were associated with4morphological traits under NaCl stress could provide the basis for MAS and QTL fine mapping. |
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