Mapping Quantitative Trait Loci For Associative Nitrogen Fixation Ability In Rice Rhizosphere And The Related Traits

Application of chemical fertilizer has promoted a great development in agricultural production. However, injudicious use of chemical fertilizer, especially chemical nitrogen fertilizer has induced a crucial negative impact to sustainable agriculture development, such as decrease of fertilizer utilization efficiency, reduction of agricultural product quality, and environmental pollution. Compared with the use of chemical nitrogen fertilizer, biological nitrogen fixation dispense with non-renewable resource. The products of N2-fixation could be directly assimilated and utilized by plants, so it is hard to be lost by volatilization, denitriflcation and eluviation from agro-ecosystem. Therefore, exhumation and utilization of biological nitrogen fixation in agro-ecosystem is particularly important to sustainable agriculture development. According to the results of field and pot experiments reported, inoculation with associative nitrogen-fixing bacteria can increase nitrogen concentrations in tissues, and biomass and grain yield of rice plants. But the response of inoculation for different rice genotypes showed great difference. The establishment of high efficient associative nitrogen-fixing system in rice rhizosphere, depends not only on inoculation with high nitrogen-fixing efficient bacteria strain, but on rice genotype that could effectively promote associative nitrogen fixation at rhizosphere as well. Hence, it is essential to find out the genetics background that controls the capacity of associative nitrogen-fixing in rice rhizosphere.A recombinant inbred lines (RIL) population and two strains of nitrogen-fixing bacteria denoted as W12 and FY were used in this study to detect the QTLs for associated nitrogen fixation capability by means of Spermosphere Model technique on condition of gnotobiotic culture. The RIL population (F11)consisting of 241 lines were developed by single seed descent procedure from a cross between an indica variety Minghui 63 (MH63) and an indica variety Zhenshan 97 (ZS97). The strain W12 with higher nitrogenase activity is isolated from cotton rhizosphere in Egypt. The strain FY, ACCC10084 is provided by Chinese Academy of Agricultural Sciences. Based on the molecular marker linkage map of RIL population generated by National Key Laboratory of Crop Genetic Improvement of Huazhong Agricultural University, QTLs for associated nitrogen fixation capability in rice rhizosphere and some related traits are detected using the program MAPMAKER/QTL. The resulted obtained are as follows:I. Modification of assay method for nitrogenase activity of associative nitrogen-fixing system in rice rhizosphere1. It is necessary to select a proper associative nitrogen-fixing period in the Spermosphere Model system after C2H2 injected for testing the nitrogenase activity of a batch of specimens. After inoculated with nitrogen fixing bacteria culture for 24h, 10% of the air in system was replaced by C2H2, then the amount of C2H4 reduced from C2H2 by nitrogenase in the system was detected by GC-14B of SHIMADZU CORPORATION at 24h, 48h, 60h, 72h, 90h and 120h after C2H2 injected. It was found that the amount of C2H4 was significantly increased from 24h to 48h, and the increment of C2H4 was not evident from 60h to 72h. So it is reasonable to finish nitrogenase activity detecting of a batch of specimens within 60 to 70h after C2H2 injected.2. For further ensuring the veracity of Acetylene reduction assay (ARA) in detecting numerous specimens, it is judicious to find a reagent to interdict the activity of nitrogenase catalyzing the acetylene reduction reaction in an associative nitrogen-fixing system at certain period. The effect of 3 bactericides with 2 concentrations each to restrain the growth of W12 and FY were test by means of the inhibition zone method. The results indicated that 3.5% formaldehyde, 2.6% sodium Hypochlorite and 0.1% mercuric chloride showed higher restricting effects and the best one is 3.5% formaldehyde.3. The bactericides selected previously were use...