| Rice has an important role in the grain production of our country and the world, the safety of rice production is important for food security. Hunan is the granary of our country, But it is very prominent for the rice which contains a large amount of cadmium. In addition, because of the high yielding cultivation mode of rice, we should pay attention to energy consumption and potential environmental problems caused by unreasonable application of nitrogen. We collected eight rice samples to isolate and identify rice endophytic diazotrophs and find the advantages. At the same time, we studyed the biological characteristics of these isolated strains and its influence on the cadmium accumulation of rice seedlings through potted plant experiment. We expected to find excellent bacterial resources for the safety of rice production. The main results are as follows:Isolation、identification and phylogenetic analysis of rice endophytic diazotrophs: there are 416 bacterias were isolated from rice root、stem、leaf and rhizosphere. After amplifying 、sequencing and blasting of 16 S r RNA, we found that these strains are from 39 generas and 136 species. Bacillus and Paenibacillus are dominate generas, Microbacterium, Pseudomonas, Fictibacillus and Flavobacterium are also have a big number. The types and number of these strains were different in different parts of rice and the root has the most. We found 330 strains that could amplificate nif H genes.The character of Biolog identification、produce spore and enzyme:We found the using map of carbon source of isolated strains by using Biolog experiment. Most of the tested strains could grow using starch as carbon source, Bacillus genus might use less carbon source than other bacteria, but Bacillus have stronger resistance. 22 strains could grow well and produce spores in 48 in beef paste ℃and nitrogen-free medium. There were 47 strains included Bacillus and Paenibacillus which could break down cellulose. Bacillus Was main source for producing extracellular proteases. There were 8 endophytic diazotrophs which can produce ACC deaminase, its activity were 0.19~1.68μmol/mg/h.The antagonism of plant pathogenic fungi and the tolerance of pesticide and antibiotic:Our results showed that there are 18 endophytic diazotrophs have antagonism to Fusarium graminearum ACCC36249, 18 endophytic diazotrophs have antagonism to Fusarium sporotrichioides ACCC37402, 9 endophytic diazotrophs have antagonism to Rhizoctonia solani ACCC36246 and inhibition rates were all higher than 33%. Some endophytic diazotrophs had tolerance to pesticides and antibiotics, they could grow in the high level of pesticides and antibiotics in the culture medium. Strains showed different abilities to tolerate the pesticides and antibiotics. Most of the strains had strong tolerance to Fludioxoni.The influences of endophytic diazotrophs inoculation on rice seedlings Cd accumulation: 48 strains were measured in greenhouse, the results showed that the scope of cadimum in rice seedings after endophytic diazotrophs inoculation was 5.40±2.30~11.45±6.58 mg/kg, compared with the CK(8.27±0.39 mg/kg), it changed-35%~39%, Which indicate that these endophytic diazotrophs can affect the rice seeding Cd absorption, it has positive significance for the screening of effective strain and control Cd into rice.The study found that rice endophytic diazotrophs has abundant diversity of genetic and functional.We not only isolated many kinds of endophytic diazotrophs, but also found that many Bacillus can produce spore and enzyme, has ability to antagonism phytopathogenic fungi and has the tolerance of pesticde and antibiotic. Some bacterials has one functional but the others may have more. Potted experiments also showed that rice endophytic diazotrophs plays an important role in control the cadimum pollution of rice. |
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