Germplasm Evaluation, Screening Of The Salt Tolerance In Rapeseed At The Germinatin Stage And Root Transcriptome Analysis Under Salt Stress

The increasingly soil salinization seriously reduces crops productivity, which is a great problem for the modern world agriculture. Research proves that improving the levels of crops’ salt tolerance may be one of the most efficient methods to ease that dilemma. Rapeseed is one of the most important oil crops in the world and acconts for more than half of the domestic pant oil production, which plays an important role in maintaining of the food security in China. And moreover, in the world of arid and semi-arid area, salt stress could decrease its yield up to 60 percent. This study has made the following outcomes on some aspects of salt-tolerance evaluation, germplasm acquisition and salt-stress-related genes through salt treatments on rapeseed varieties(or lines) at the germination stage.(1) Fifteen B. napus genotypes were stressed by gradient Na Cl concentrations and six physiological characteristccs including germination percent(GP), germination potential(GPO), root length(RL), hypocotyl length(HL), plantlet fresh weight(PFW) and up-ground fresh weight(UFW) were tested at the germination stage. Results showed:(a) The relative GP changed in Boltzmann curve with various Na Cl concentrations. The concentration of 214 mmol/L was defined as the optimum concentration for evaluating the salt tolerance of B. napus.(b) The six traits were affected by salt stress. And each line was inhibited by salt stress with different degrees. There were significant differences among the lines.(2) A total of 67 Chinese varieties were used to evaluate the salt tolerance by at the germination stage. Results showed:(a) The significant differences existed among rapeseed varieties based on the salt tolerance coefficient(STC) values of 11 traits.(b) The salt tolerance of hybrid varieties was higher than that of pedigree ones, but no difference were found in salt tolerance of varieties originated from up, middle and down streams of Yangtze River basin, the famous rapeseed belt in the world.(c) A consist result lied between PCA and clustering methodology on evaluating of varieties salt tolerance generally. Zhongyou821 and Naiyan1 were approved as highly salt-tolerant varieties, Xiangyou15 and Huashuang3 were highly salt-sensitive ones.(3) For exploring the salt tolerance levels of different species of rapeseeds and screening tolerant germplasm, a total of 203 accessions of three cultivated species(B. juncea, B. rapa and B. napus) were stressed by Na Cl concentrations. Results showed:(a) The GPs of three species were all inhibited but with different degrees under salt stress and B. rapa was most tolerant, which followed by B. napus and B. juncea sequentially in general.(b) Six physiological characters of fourteen lines from three species were tested and Br2 of B. rapa and Bn1 and Bn3 of B. napus were the best salt-tolerant germplasm which could be used in the future breeding application.(4) Roots of the salt-tolerance line WH126 were treated by H2O(control) and 214 mmol/L Na Cl solution(salt treatment) at the germination stage. And the digital gene expression(DGE) technique was explored on roots at 0, 3, 12 and 24 hours after treatments. Results showed that the root length was severely inhibited by salt treatment. Comparisons of gene-expression between the control and the treatment were conducted after tag-mapping to the sequenced B. rapa genome. The differentially expressed genes during the time course of salt stress were focused on, and 163 genes were identified to be differentially expressed at all the time points. Gene Ontology(GO) and Kyoto Encyclopedia of Genes and Genomes(KEGG) enrichment analyses revealed that some of the genes(Pro DH, P5 CS, MIOX, P450, 2OG oxygenase, XTH and etc.) were involved in proline metabolism, inositol metabolism, carbohydrate metabolic processes and oxidation-reduction processes and may play vital roles in the salt-stress response at the germination stage. Thus, this study provides new candidate salt stress responding genes, which may function in novel putative nodes in the molecular pathways of salt stress resistance.