| Rhizobium-legume symbiotic nitrogen fixation system is the biological nitrogenfixation system possessing the highest nitrogen fixation efficiency and output in nature.Biological nitrogen fixation is the most important strength of soybean, unlike other crops.Planting soybeans leads to less fertilizer, soil fertility, improvement of soil. Yellow RiverDelta region is characterized by sparse vegetation, and ecological fragility, a large numberof salinized lands, much of the land soil with more than 1% salinity, and weakly alkalinesoil. There are a certain number of wild soybeans (Glycine soja) growing in the fashion ofscattered chip. The wild soybean is an annual herb, closely related species of cultivatedsoybean, possesses good traits such as salt and alkali resistance, cold hardiness resistance,disease resistance, and rich nutrient and so on.To better protect and utilize the valuable resources of the wild plants, as early as 2004,wild soybean Nature Reserve in the Yellow River Delta was set up. Presently, the researchinto the wild soybean rhizobia in this region is rarely reported. We, from more than 20sampling points of the vicinity of this region, collected more than 200 strains of wildsoybean, from the root nodules of which 100 strains of rhizobia were isolated and purified.These 100 strains were systematically studied by a series of surveys of stress resistance,nodulation capacity, the nodulation broad spectrum and diversity of wild soybean rhizobia.The concrete results of this paper are as follows:1. Congo red medium experiments, beef extract protein peptone medium experiment,3-keto-lactose medium experiments, citrate medium experiment, the BTB experiment, milklitmus test and the sole nitrogen source experiment are conducted to further determinatelydistinguish Rhizobium Genus and other soil bacteria which are easily confused withRhizobium Genus. According to the measured physiological and biochemicalcharacteristics and the length of culture time of wild soybean rhizobia, the strain coded as7K-8 is classified as Bradyrhizobium genus, and the rest strains are classified as fastgrowing rhizobia genus.2．Tolerance of these 100 strains for acid, alkali, salt, antibiotic and temperature aretested to demonstrate that: 100 strains of the isolated and purified Rhizobia vary in thestress resistance. Among them, strain 3D-21, 3D-24, 3K-3K-23 possess particularly weaktolerance, while K-5 etc. possess strong tolerance for acid, alkali, salt, antibiotic, hightemperature and low temperature. These provide the basis of breeding high-quality strainswith stress resistance.3.Tieback test results of these more than 100 strains show that although they havecertain nodulation capacity, there are some differences in the size aspects of nodulation capacity. And the tests of their nodulation broad spectrum demonstrate that these strainscan only make wild soybean plants nodulate, and can’t make peanut and broad bean plants,the same legumes as wild soybean, nodulate, indicating that these strains have nodulationspecificity.4.We select several strains of fast-growing rhizobia and Bradyrhizobium coded as7K-8, which have stronger nodulation capacity, and compare their stress resistance andnodulation capacity. The results show that although the Bradyrhizobium 7K-8 hasobviously lower growth rate and stress resistance than the fast growing rhizobia, itsnodulation capacity is not worse than the fast growing rhizobia, and this is perhaps relatedto its strong viability, plump lawn and uneasy degradation.5.We, by 16S rDNA sequencing and physiological and biochemical experiments,determine that these over 100 strains of Rhizobium belong to Sinorhizobium, cowpeaRhizobium, Bradyrhizobium, which belong to theα- proteus, respectively. Among these,Sinorhizobium, which accounts for a higher proportion up to 98%, is the dominant flora ofthe region6.Using RAPD technique, we test more than 30 strains of Sinorhizobium, and theresults show that there are still significant differences among the strains of the samespecies. |
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