Evaluation Of Rapeseed Drought Tolerance At Different Developmental Stages And Accociation Mapping By Transcriptomics

Rapeseed, the most important winter oil crop in China, requires a lot of water during the life cycle and is heavily affaced by drought stress. In China, most of the rapeseed is planted across the Yangtze River Valley. The Yangtze River Valley frequently experiences drought stress in the autumn and spring, coinciding with the rapeseed seedling stage and the reproductive stage, respectively. This drought stress had critical influence on the seed yield. However, a deep- and systematic- study on drought resistance of rapeseed is still lacking. Therefore, studying the drought tolerant between seedling and reproductive stages will certurnly lead to the establishment of methods for the early screening of drought-resistant genotype. Moreover, it will also help to difine the drought resistant candidate genes by genome wide association mapping, which will provide the key materials and technical support for rapeseed breeding and industry development.This project studied the different responses to seeding stage and the reproductive stage under drought stress, defined the relationship between the seed yield and the yield component factors, explored the drought resistance between seedling stage and the reproductive stage, and evaluated the correlation between the indicator of drought tolerance and seed yield. A novel association mapping methodology termed ‘Associative Transcriptomics’（AT） was applied to define genetic regions underlining drought tolerance candidate genes. The main results are as follows:1) The impact of water deficit imposed at the germination stage or the reproductive stage on biological traits of 37 semi-winter rapeseed varieties was analyzed. The osmotic stress induced by 14% polyethylene glycol had a substantial impact on seed germination and caused a significant reduction in plant growth and seed vigor. Relative water content was highly correlated with seed yield and DSI, Which indicate the relative water content can be a good indicator for early screening of drought resistance.At the reproductive stage, the result show that seed yield, 1000-seed weight, height of the first branch, plant height, and number of pods per plant were all markedly changed, which caused 78.7%, 35.8%, 28.5% and 7.03% reduction, respectively. Base on drought stress index, 3 drought tolerant and 21 drought sensitive and 13 moderate drought accessions were identified. Path analysis was employed to rank the relative importance of other agronomic traits with regard to seed yield. The important contributors to seed yield under drought conditions, in descending order, were as follows: 1000-seed weight, days to maturity, number of pods per plant, and plant height.2) The effects of drought stress on the rapeseeddiversity panel were analyzed. The objective of this task was to evaluate drought resistance of the 79 rapeseed lines by polyethyleneglycol（PEG6000） during germination period. The results indicated that the fresh weight of the aboveground was significant reduce, and the relative activities of SOD, CAT, POD and proline were also significant reduce. Investigations were also carried out to record the responses of the temperature of leaves and the leaf SPAD values. The result showed that both the drought-resistant varieties and sensitive lines were all significantly increased in the early stage of drought stress, and with the stress time and concentration of PEG increasing, drought resistance lines show higher temperature than drought sensitive lines. Base on D value, 8 drought tolerant and 39 drought sensitive and 32 moderate drought accessions were identified. This result was verified by the percentage of seedling survival experiment. Correlation analysis between D value and the drought resistance index showed that it was feasible to use the relative water content, the fresh and dry weight of the overground and the fresh and dry weight of the underground as an indicator of drought tolerance at seeding stage.3) Associative transcriptomics was applied to define genetic regions and drought tolerance candidate genes. By this approach, 144131 informative single-nucleotide polymorphisms（SNPs） and 100534 gene expression markers（GEMs） were developed which enabled the identification of loci significantly associated with dourght tolerance. Within these loci, 4 genes were inferred to be drought tolerance candidate genes. These drought tolerance candidate genes are JCVI₁7979、JCVI₁8549、A_JCVI₁1915 and JCVI₁9909.