Xiao Deng

The Degradation Dynamics of Acetamiprid in Hainan Cowpea and the Soil

The HPLC method for acetamiprid in soil and cowpea was developed. The degradation dynamics of the acetamiprid in the soil and cowpea and the last residue in the cowpea were researched. The method recovery was 81% - 88% and the linear relationship was good from 0.05 to 5μg·mL-1 with a CV less than 5%, which could meet the detection requirement. The half-life of the acetamiprid were 3.3 days and 4.1 days, respectively in soil and cowpea. The residue of the acetamiprid in the cowpea was less than 0.5μg·g-1 4 days later when two times of the recommended dose. The half-life of the acetamiprid was short, which belongs to the easy degradation pesticide. The cowpea was sprayed 3 times, respectively with two times and 2.5 times of the recommended dose, which had a two days interval each time. The results showed that 4 days and 6 days later the acetamiprid residue in the cowpea were less than 0.5μg·g-1.

Kocuria Rosea HN01: A Newly Discovered Alkaliphilic Humic-Reducing Bacteria Isolated from Cassava Dregs Composting

The aims were to isolate a humus-reducing microorganism from cassava dregs composting and to investigate the main factors affecting humus reduction rate by the isolate. A halotolerant and alkaliphilic humic-reducing strain, designated as HN01, was successfully isolated. The strain was facultatively anaerobic, Gram-positive, coccus-shaped, and identified as Kocuria rosea with 16S rRNA analysis. Microbial growth was observed at NaCl concentrations below 12% (w/v), pHs of 6–10, and temperatures of 15–30°C under aerobic condition. HN01 was capable of anaerobic reducing humic substance analogs, anthraquinone-2,6-benzene sulfonic acid (AQDS), with glucose, sucrose, methanol, ethanol, or glycerol as an electron donor, and the reduction rates were 46, 42, 40, 41, and 37%, respectively, within 48 h at pH 8.5. Organic substrates such as formate, acetate, propionate, and citrate were not available electron donors with respect to AQDS reduction. The range of pHs and NaCl concentrations for humus reduction by strain HN01 were pH 7–10 and NaCl% (w/v) 1–10%; pH 8.5 and 3% NaCl were the optimum.

Soil Microbial Functional Diversity from Different Infection Grades of Banana Fusarium Wilt (Fusarium oxysporum f. sp. Cubense)

Thirty rhizosphere and non-rhizosphere soil samples from different infection grades(0, I, III, V and VII) of three typical banana plots(Jianfeng, Shiyuetian, Chongpo) infected by banana fusarium wilt (Fusarium oxysporum f. sp. cubense) in Hainan province were collected to study the microbial community functional diversity applying Biolog-ECO microplates technology. The results are as follows: (1) Overall carbon source metabolic capacities of soil microbial community weaken with increasing of infection grades of banana fusarium wilt. (2) Richness indices, Simpson indices, Shannon indices and McIntosh indices of soil microbial community gradually decreased with increasing of infection grades of banana fusarium wilt. (3) Principal component analysis show that metabolic characteristics of soil microbial community significantly change between the healthy plants and diseased plants in the same banana plot. The results would provide information for explaining the pathogenesis of banana fusarium wilt and controlling its incidence by applying microbial ecology to regulate soil environmental measures.

Study on the Effects of 8 Strains on Growth Promotion and Disease Resistance of Tomato (Solanum lycopersicum)

The pot experiment was carried out to study the effects of eight functional strains on growth promotion of tomato and resistance to tomato bacterial wilt. The results indicated that the two strains both Paenibacillus polymyxa and Bacillus megaterium could significantly increase the plant height of tomato; the two strains of Paenibacillus azotoformans and Bacillus laterosporus could significantly improve the stem diameter of tomato; the three strains of Paenibacillus polymyxa, Bacillus laterosporus and Paenibacillus azotoformans could significantly increase the average leaf area and chlorophyll contents of Tomato; the four strains of Bacillus subtilis, Bacillus licheniformis, Paenibacillus polymyxa and Streptomyces microflavus could obviously inhibit occurrence of tomato bacterial wilt. All above results indicated that Paenibacillus polymyxa could not only significantly increase the height, the average leaf area and chlorophyll content of tomato plant, but also could obviously reduce the incidence of tomato bacterial wilt. So this strain can be used as one of core strains to construct multifunctional composite inoculants.

Isolation and Characterization of Paraquat-Degrading Extracellular Humus-Reducing Bacteria from Vegetable Field

The aim of this paper is to isolate pure cultures that are capable of degrading paraquat (PQ) anaerobically with humic substances (humus) as the sole electron acceptor. Three facultative anaerobic bacteria (PQ-1, PQ-2, and PQ-3) were successively isolated from vegetable soil in Sanya city, China, via enrichment procedure with PQ and anthraquinone-2,6-disulphonate (AQDS) under anaerobic conditions. Batch experiments were conducted to investigate isolates PQ anaerobic degradation activity. Results showed that three strains were all capable of degrading PQ directly with AQDS as the sole electron acceptor (18.6% removal within 48h), and the microbial process might be AQDS dependent. The addition of low molecular weight organic substrate, such as sucrose, could enhance the anaerobic degradation of PQ from 18.6% to 34.2%, and the degradation rate reached 100% after 5-day incubation. This study was the first paper reporting that pure cultures have the ability to anaerobically degrade PQ with AQDS as the sole electron acceptor.

Residual Characteristics of Organochlorine Pesticides in Vegetable Soils from the Middle of Yuanmou

The aim of this paper is to analyze the characteristics of organochlorine pesticides (OCPs) residues in vegetable soils from the middle of Yuanmou. 12 surface soil (0~20 cm) samples of vegetable fields soil were collected and 18 types of OCPs in soil were analyzed by gas chromatography Results show that excepting for α-endosulfan, endrin, aldrin, o,p’-DDT and p,p’-DDT, other 13 types of OCPs was found with different degree in all the samples. The detection rate of 18 types of OCPs was nd~100%, the residue level was nd~11.76 μg•kg-1, OCPs residues were main chlorthiepin sulfate, HCHs and dieldrin. Residues of endosulfan, HCHs and dieldrin in the soils might come from the old usage and residues of heptachlor might come from the recent usage. Contamination of OCPs in soils from the middle of Yuanmou were relative lower than most areas in south of China.

Influence of the Number of Pathogen Causing Banana Fusarium Wilt and Soil Factors on the Infection Degree of Banana Plants

Banana fusarium wilt is one of the soil-borne diseases of seriously threat to banana production in the world. However, there is no effective method for prevention. The objective was providing theoretical basis for field diagnosis of banana fusarium wilt. Thirty rhizosphere and non-rhizosphere soil samples were collected from three typical banana plots (Jianfeng, Shiyuetian, Chongpo) infected by banana fusarium wilt. Applying dilution plate method to estimate the pathogenic number, fourteen soil physicochemical properties and nutrient concentrations were chemically determined. Results showed that pathogenic number and nutrient concentrations in rhizosphere soil were higher than non-rhizosphere soil, the pathogenic number and pH in rhizosphere soils significantly increased with increasing of plant infection grades, while the concentrations of available P and B decreased with increasing of plant infection grades. It was concluded that infection degree of banana plants was mainly determined by pathogenic number, pH and the concentrations of available P and B.