The Investigation Of Indigenous Soybean Rhizobia In Five Provinces Of South China And Study Of Quorum Sensing In Noudulation

The symbiosis formed by rhizobia and legume host plays an important role in agriculture. The application of rhizobia inoculant can drastically reduce the dose of chemical nitrogen fertilizer and decrease the environmental pollutions. It's well known that the application effect of rhizobia inoculant in soybean-uncultivated field is more significant higher than that in soybean-cultivated farm. The application effect of rhizobia inoculant in soybean-cultivated soil is determined, in most extent, by the nusmber of indigenous rhizobia population. So it is difficult to reach the ideal aim and also is blind if we did not investigate the resource of indigenous rhizobia before the application of rhizobia inoculant.The number of indigenous soybean rhizobisa was measured and the proportion of fast- and slow-growing soybean rhizobia was determined from the 15 soil samples collected from Guangxi, Anhui, Jiangsu, Guizhou provences and Chongqing City. The results showed that (1) The number of indigenous soybean rhizobia in soybean-cultivated soil was significantly higher than the one in soybean-uncultivated soil; (2) In comparison with the nodulation ability, the local cultivar was higher than the foreign cultivar; (3) The proportion of fast- and slow-grower was affected weakly by the pH value of soil when the pH value was ranged from 4.0 to 8.0.High effective rhizobia should also have strong competition ability. The factors that influence the competition ability of rhizobia come from not only environment, but also rhizobia itself.A special pair of conservative primers and a pair of complete gene primers were designed based on the released nolA gene (Genbank Accession No. AF322013) sequence of Bradyrhizobium japonicum. PCR and sequencing results showed that Sinorhizobium fredii strain HH21 contained nolA gene, too. Nodulation repression was also proved in S. fredii strain HH21 by both of pot and test tube plant nodulation experiments. This character is triggered by the expression of nolA gene in B. japonicum and controled by the pathway of population density-dependent regulation. These results offer a hint to improve the competition ability for commercial rhizobia inoculant.