Phân lập, tuyển chọn và định danh vi khuẩn liên kết với thực vật (plant associated bacteria) ở lúa, khoai trồng trên đất phèn ở đồng bằng sông cửu long tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY DOCTORAL THESIS SUMMARY Specialized: Soil Science Code: 9620103 LY NGOC THANH XUAN ISOLATION, SELECTION AND IDENTIFICATION PLANT ASSOCIATED BACTERIA AT RICE, SWEET POTATO CULTIVATED ON ACID SULPHATE SOILS IN THE MEKONG DELTA Can Tho, 2019 THE Ph.D THESIS WAS COMPLETED AT CAN THO UNIVERSITY Advisor: Assoc Prof Dr TRAN VAN DUNG Prof Dr NGO NGOC HUNG The doctoral thesis was evaluated by The Board of Examiners at basic level Meeting at: Meeting room 3, 2nd floor, administrative house, Can Tho University At 14.00 p.m, date 22/6/2018 Reviewer 1: Dr LUU HONG MAN Reviewer2: Dr CAO VAN PHUNG You can find thesis at the library: Learning Resource Center, Can Tho University National Library of Vietnam LIST OF PUBLICTION Ly Ngoc Thanh Xuan, Trinh Quang Khuong, Le Van Dang, Tran Van Dung Ngo Ngoc Hung, 2016 Applcation of plantassociated bacteria Burkholderia vietnamiensis on the growth and yield of rice crops cultivated on acid sulphate soil in the Mekong Delta Can Tho University Journal of Science, 44b: 1-8 Ly Ngoc Thanh Xuan, Tran Van Dung, Ngo Ngoc Hung,Cao Ngoc Diep, 2016.Isolation and characterization of rice endophytic bacteria in acid sulphate soil of Mekong delta, Vietnam World journal of Pharmacy and Pharmaceutical sciences,5 (8): 301-317 Ly Ngoc Thanh Xuan, Tran Van Dung, Ngo Ngoc Hung,Cao Ngoc Diep, 2016.Isolation and characterization of rhizospheric bacteria in rice (oryza sativa l.) cultivated on acid sulphate soils of the Mekong delta, Vietnam World journal of Pharmacy and Pharmaceutical sciences, (9): 343-358 Ly Ngoc Thanh Xuan, Tran Van Dung, Ngo Ngoc Hung,Cao Ngoc Diep, 2017 Isolation and characterization of endophytic and rhizopheric bacteria associated sweet-potato plants cultivated on soils of the Mekong delta, Vietnam World journal of Pharmacy and Pharmaceutical sciences, (1): 129149 Ly Ngoc Thanh Xuan, Le Van Dang, Tran Van Dung and Ngo Ngoc Hung, 2018.Applcation of plantassociated bacteria on the yield of sweet potato cultivated on acid sulphate soil in the Mekong Delta Science and Technology Journal of Agriculture and Rural Development, Ministry of Agriculture and Rural Development, Vietnam, 7: 93-103 INTRODUCTION Rationale and background Nitrogen (N) is the most essential nutrient to promote rapid plant growth and grain yield; thereby, high amounts of chemical N fertilizers have been applied to gain high crop yield in agricultural ecosystems for intensive fertilization practices (Galloway et al., 2004), especially in low-fertility soils like ASS as an example This issue faces not only environmental problems as greenhouse gas emission but also microbial communities as changes of N2-fixer growth and activity (Reardon et al., 2014; Tang et al., 2017) Therefore, a biological nitrogen source should be altered to tackle with this problem and make a use of natural resources Specifically, biological nitrogen fixation (BNF) is one of the important natural processes to fix N2 from the atmosphere into bioavailable NH4+ in the soil by nitrogenase enzyme, which is an important source of nitrogen in agricultural terrestrial systems (Peoples and Craswell, 1992; Kennedy and Islam, 2001) Normally, insufficient phosphorus (P)for rice has been observed in ASS due to immobilized P asits precipitation with free aluminum and iron ions to form aluminum phosphate (AlPO4) and iron phosphate (FePO4) (Margenot et al 2017); and this leads toless available forms of P for plants (Rengel and Marschner 2005) and altered the soil microbial community structure (Ragot et al 2016; Soman et al 2017) Hence, several tools to resolve this problem include chemical, physical and biological approaches Rice cultivation in actual ASS faced with toxicity of toxicity (Högfors-Rönnholm et al 2018) and acidic environment that cause low yield (Johnston et al 2016) The ASS can be reclaimed by physical and chemical techniques although there are many constraints of both systems such as high costs, water shortage and Cd contamination derived from phosphorus fertilizers (Chaitanya et al 2017; Shamshuddin et al 2017) However, these problems can be tackled by the endophytic bacteria and rhizobacterial strains because they possesses the ability of N2-fixation, P-solubilization from P-Al, and P-Fe sources Moreover, the efficacy of microorganism is depended on interaction between bacteria and host (Patnailk, 1994) Regarding above information, to achieve the sustainable agricultural system for solving the serious problems of rice cultivation on ASS, isolation, selection and application of endophytic bacteria and rhizobacterial strains from rice, sweet potato and their soils are necessary Objectives (i) Isolation of endophytic and rhizospheric bacterial strains associated with sweet potato and rice for abilities of nitrogen fixing, phosphate-solubilizing; (ii) Selection of promising nitrogen fixing, phosphatesolubilizing bacterial strains for improvement of sweet potato and rice growth and yield in the greenhouse and field conditions; (iii) Suggestion of promised 2-3 strains to apply on acid sulfate soil Novelty of research The without nitrogen fertilizer application decreased rice yield on acid sulfate soil in Long My – Hau Giang, Hon Dat – Kien Giang and Hong Dan – Bac Lieu, but the application of both 60 kg N ha-1 and Burkholderia vietnamiensis X1 resulted in higher rice yield compared to control treatment (90N-60P-30K) on acid sulfate soil in Hon Dat – Kien Giang Similarly, the applied B vietnamiensis X3 increased productivity in Long My – Hau Giang, and Hong Dan – Bac Lieu However, without phosphorus fertilizer application have not been improved yield by application of B vietnamiensis X1 B vietnamiensis X3 The bacterium Burkholderia acidipaludis X5 has high nitrogen fixation capability compared to those in the other bacteria through increasednumber oftubersand yield of sweet potato Applying 60kgN/hain combination with incubation ofbacteria Burkholderia acidipaludis X5 showed that the tuber number, tuberlength, tuber diameter and sweet potatoyield were equivalent with applying 90 kg N/ha Incubation with bacteria Burkholderia acidipaludis X5 could save30% of nitrogenfertilizersforsweet potato Outline of thesis content The thesis included 103 pages with chapters Chapter 1: Introduction (Pages: 1-5); Chapter 2: Literature review (Pages: 635); Chapter 3: Materials and methods (Pages: 36-58); Chapter 4: Results and discussion (Pages: 59-102); Chapter 5: Conclusions and recommendations (Pages: 103-104) CONTENT OF THESIS Chapter 1: Literature review Rice (Oryza sativa L.) is one of the most important crops in the world and paddy soil comprise the largest anthropogenic wetland on earth (Kogel-Knabner et al 2010) and the main dietary component of 20% of the world’s population (IRRI, 2010)(Seck et al., 2012); feeding more than 50% of the world’s population (Gyaneshwar et al., 2001) In the next three decades, the world will need to produce about 60% more rice than today’s global production to feed the extra billion people (Ladha and Reddy, 2003) Increases in the demand for rice, as a result of an increase in population, creates the need to improve rice productivity and one of the most important factors for high yields of rice production are chemicals fertilizers and pesticides, which may cause environmental pollution and negatively influence human health Sweet-potato (Ipomoea batatas (L.) Lam.), a dicotyledonous plant belongs to the Convolvulaceae family, is a subsistence crop which store starch in their roots and form tuberous roots It has a huge economic and social importance in developing countries (Souza and Lorenzi, 2008) with over 95% of the global sweet potato crop which is produced in developing countries (Reiter et al., 2003) It also is resilient, easily propagated crop, growing well in infertile and nitrogen (N) poor soils (Khan and Doty, 2009) Besides rice and fruit plants, sweet potato plant also is cultivated popularly on alluvial soil in the dry season as crop for food and exporting in the Mekong Delta, Vietnam Sweet potato area occupied 21,500 (9.3% sweet potato area in Vietnam) with yield over 20 tons/ha in the Mekong Delta (Agricultural Statastic in 2010) In the kinds of chemical fertilizers, substances composed of known quantities of nitrogen, phosphorus and potassium, keep an important role in the growth and yield of crops as high-yielding rice Nitrogen (N) is one of the most important nutrients in plants and is a limiting in plant growth and development and available phosphorus (P) deficiencies in many parts of the world (Fageria et al 2011) also is the limiting factor for rice growth and development especially root development, poor flowering and lack of seed etc., consequently causing degradation in quality and quantity (Ji et al 2014) Soil is replete with microscopic life forms including bacteria, fungi, actinomycetes, protozoa and algae Of these different microprganisms, bacteria are by far the most common (i.e., 95%) It has been known for some time that the soil hosts a large number of bacteria (often around 108 to 109 cells per gram of soil) and that the number of culturable bacterial cells in soils is generally only about 1% of the total number of cells present (Schoenborn et al 2004) They are involved in various biotic activities of the soil ecosystem to meke it dynamic for nutrient turn over and sustainable for crop production (Ahemad et al., 2009) Most plants depend on soil, but plants and their associated microorganisms also play a crucial role in the formation or modification of soil (Pate and Verboom, 2009; Taylor et al., 2009) and microorganisms present in the rhizosphere play important roles in the growth and in the ecological fitness of their plant host (Buee et al., 2009) Microbial interactions with roots may involve either endophytic or free living microorganisms and can be symbiotic, associative or casual in nature; beneficial microorganisms include N2-fixing bacteria in association with legumes and interaction of roots with mycorrhizal fungi and phosphate-solubilizing microorganisms in relation to plant P uptake, enhancement of root growth (Raaijmakers et al, 2009).Therefore, the plant growth promoting rhizobacteria (PGPR), are characterized by the following inherent distinctiveness’s: (i) they must be proficient to colonize the root surface (ii) they must survive, multiply and compete with other microbiota, at least for the time needed to express their plant growth protion/protection activities, and (iii) they must promote plant growth (Kloepper, 1994) Endophytic bacteria are microorganisms that live in plant tissues and they may be responsible for the supply of biologically fixed nitrogen to their host plant (Boddey et al., 2005) Endophytes also promote plant growth by a number of similar mechanisms as phosphate solubilization activity (Waklin et al., 2004), indole acetic acid production (Lee et al., 2004) and the production of a siderophores (Costa and Lopez, 1994) Recently, the potential for microbes to increases nutrient availability and to enhance crop growth has garnered the attention of the researchers, and the increasing reliance on biological processes and plant interactions with microbes through ‘ecological intensification’ may be one of the most promising strategies to overcome these problems (Yang et al 2014) Bio-fertilizers containing efficient microorganisms, improve plant growth in many ways compared to synthetic fertilizers, by way of enhancing crop growth, sustainability of environment and crop productivity and efficient microbes with PGPR and endophytic bacteria have been produced as bio-fertilizer for crop production in sustainable agriculture (Bhardwaj et al 2014) In the Mekong Delta is the main area of food production of crucial importance of ensuring national food security and agricultural product export (Dan et al., 2015), it has more than millions hectare but area of rice production only occupied 1,9128 millions hectare (46.9%)(MRE, 2014) and acid sulphate soil occupied millions hectare with regions Chapter 2: Materials and methods 2.1 Materials Rice, sweet potato samples were collected from Long Xuyen Quadrangle, Plain of Reed, Depressed of Hau River and Ca Mau Peninsula, Mekong Delta, Vietnam, their soils were also collected at corresponding sites Media were used to isolate plant associated bacteria at rice, sweet potato and rhizospheric soil as Burk, NBRIP, LGI, NFb Bacterial identification from rhizospheric soil: use a pair of primers as Forward Primer 8F and Reverse Primer 1492R (Turner et al., 1999) 8F: 5’- AGAGTTTGATCC TGGCTCAG-3’ 1492R:5’-TACGGTTACCTTGTTACGACTT-3’ Bacterial identification from rice, sweet potatoendophytic bacteria: use a pair of primers as P515FPL and P13B (Zinniel et al., 2002): P515FPL: 5’- GTGCCAGCAGCCGCGGTA A -3’ P13B: 5’- AGGCCCGGG AACGTATTCAC -3’ 2.2 Methods 2.2.1 Sample collection Rice and rice rhizospheric soil samples were collected from Long Xuyen Quadrangle, Plain of Reed, Depressed of Hau River and Ca Mau Peninsula For sweet potato samples were also collected from areas, the exception for Ca Mau Peninsula 2.2.2 Isolation and selection of endophytes with nitrogen fixation and P solubilization Media were used to isolate plant associated bacteria including Burk, NBRIP, LGI, NFb; for biofertility activities were Burk’N free; and insoluble P as Al-P and Fe-P were added to NBRIP’P free 2.2.3 Bacterial identification The selected bacteria isolated from both plant and soil were identified by 16S rDNA sequence analysis The amplified PCR products were purified using a Invitrogen Kit as described by the manufacturer’s guide The sequencing results along with the chromatograms were analyzed using BioEdit, version 7.0.5.3 and ChromasPro version 1.7 The corrected sequences were compared tothe available sequences in the GenBank database for the determination of the most similarity by Basic Local Alignment Search Tool (BLAST) of National Center for Biotechnology Information (NCBI) website Multiple sequence alignments were done using CLUSTALW then neighbor-joining phylogenetic tree was reconstructed using MEGA software, version 6.06, wherein evolutionary distance matrix was calculated by Jukes–Cantor model and topologies of the neighbor-joiningtrees were calculated by bootstrap resampling method based on 1,000 replicates 2.2.4 Selection of potential bacteria for field application The indentified bacteria sequenced was used to confirm the ability for nitrogen fixation from Burk’s N free and phosphorus solubilization from Al-P and Fe-P instead of adding Ca-P under acidic medium; strains for each plant was selected to apply on acid sulfate soil in paddy field and sweet potato 2.2.5 Evaluation of efficacy of selected bacterial strains on paddy field on acid sulfate soils Experiment 1: Effects of selected bacterial strains (VK1, VK2, VK3) and nitrogen fertilizer rates on rice yield in summer-autumn 2015 A x factorial experiment was carried out in a completely randomized block design including the main factor of inoculants (VK1, VK2, VK3) and the minor factor as N fertilizer rates (30N, 60N, 90N) to have a total of treatments, with replications from 20 m2 for each plot Treatments are shown in Table 2.1 Table 2.1: Effects of selected bacterial strains and nitrogen fertilizer rates on rice yield in summer-autumn 2015 N rate (kg/ha) 30 60 90 Tested bacterial strains VK1 NT1 NT4 NT7 VK2 NT2 NT5 NT8 VK3 NT3 NT6 NT9 P and K fertilizes was applied as recommendation as follows: 60P2O5 - 30K2O kg ha-1 Experiment 2: Evaluation of promised bacterial strains on rice yield in autumn–winter 2015 in the Mekong Delta An experiment has been conducted in a completely randomized block design including six treatments, with replications from 20 m for each plot Treatments are shown in Table 2.2 sequence analysis The phylogenetic analysis is belonged to Bacilli, Gammaproteobacteria and Betaproteobacteria groups Similarly, The 12 selected sweet potato, yam, and cassava endophytic bacterial strains had high promised capacities for nitrogen fixing, phosphatesolubilizing, which were identified by 16S rDNA sequence analysis The phylogenetic analysis is closely classified to Bacilli and Gammaproteobacteria groups From selected 15 and 20 rice endophytic bacteria and rhizobacterial strains having high nitrogen fixation capacity and P solubilization, respectively, under neuter broth (pH 7.0), they were used to evaluate both abilities under acidic medium (pH 4.0) The results showed that all strains have ability of nitrogen fixation, and P solubilization from Al-P and Fe-P Strains KG2-21, HG6-21b and BL1-21b produced 0.79 – 1.38 mg NH4+ L-1 at DAI Similarly, PO43- was produced 22.2 – 58.1 from Al-P source and 24.9 – 48.9 mg L -1 from Fe-P source (Table 3.1) Table 3.1: Ability of nitrogen fixation and P solubilization from Al-P and Fe-P sources at pH 4.0 by selected endophytic rhizobacterial strains in rice Days after incubation ASS area Strain NH4+ (mg L-1) KG2-21 1.51 1.49 1.83 1.37 AG5-13 0.25 0.66 0.88 0.73 Long DT10-12a 0.33 0.37 0.42 0.34 Xuyen AG8-13 0.28 0.30 0.35 0.29 Quadrang AG9-22 0.16 0.21 0.22 0.25 le KG5-3a 0.20 0.23 0.21 0.25 AG5-3 0.21 0.23 0.22 0.25 AG9-4b 0.17 0.23 0.18 0.27 Plain of LA2-21b 0.45 0.52 0.60 0.56 Reed LA5-22b 0.17 0.39 0.34 0.33 DT9-11 0.26 0.35 0.33 0.43 LA4-3b 0.31 0.29 0.36 0.29 LA5-3 0.25 0.40 0.41 0.34 11 Depresse d of Hau River Ca Mau Peninsula ASS area Long Xuyen Quadrang le Plain of Reed Depresse d of Hau River LA4-3c HG6-21b HG9-3a HG10-3a VL3-21 VL4-12 VL3-3b VL3-3c BL1-21b BL5-12 CM7-22 BL2-21b BL3-4a BL4-3 BL5-4b BL5-3 0.22 1.06 0.47 0.32 0.15 0.12 0.19 0.16 1.51 0.44 0.11 0.18 0.17 0.17 0.33 0.27 Strain KG2-21 AG5-13 DT10-12a AG8-13 AG9-22 KG5-3a AG5-3 AG9-4b LA2-21b LA5-22b DT9-11 LA4-3b LA5-3 LA4-3c HG6-21b HG9-3a HG10-3a VL3-21 VL4-12 VL3-3b 73.9 10.03 21.35 12.98 14.56 11.26 11.70 10.32 24.5 14.21 9.58 11.05 18.06 11.00 145.0 44.3 33.2 15.1 7.9 11.8 12 0.30 0.28 0.91 0.81 0.64 0.60 0.28 0.54 0.33 0.62 0.29 0.44 0.18 0.42 0.15 0.35 1.48 1.82 0.76 0.78 0.33 0.28 0.16 0.33 0.32 0.20 0.13 0.18 0.31 0.31 0.24 0.47 P-Fe (mg L-1) 10 15 32.8 27.5 9.00 8.70 18.68 16.36 4.33 3.85 5.47 4.61 10.50 10.54 10.90 10.90 14.21 15.55 10.1 9.2 7.00 6.37 3.72 3.35 4.67 5.80 10.84 11.88 9.28 9.11 63.2 55.8 26.6 29.1 22.5 25.6 16.8 22.1 9.8 17.8 8.9 4.5 0.31 0.79 0.81 0.45 0.33 0.37 0.38 0.32 1.38 0.62 0.51 0.49 0.21 0.21 0.33 0.34 20 22.2 9.95 13.36 2.60 3.33 13.60 13.30 16.69 5.4 7.15 1.78 3.78 14.04 4.12 58.1 34.4 22.6 22.3 18.8 1.0 Ca Mau Peninsula ASS area Long Xuyen Quadrang le Plain of Reed Depresse d of Hau River Ca Mau Peninsula VL3-3c BL1-21b BL5-12 CM7-22 BL2-21b BL3-4a BL4-3 BL5-4b BL5-3 9.8 135.7 22.8 16.9 13.4 10.14 10.50 1.78 2.28 Strain KG2-21 AG5-13 DT10-12a AG8-13 AG9-22 KG5-3a AG5-3 AG9-4b LA2-21b LA5-22b DT9-11 LA4-3b LA5-3 LA4-3c HG6-21b HG9-3a HG10-3a VL3-21 VL4-12 VL3-3b VL3-3c BL1-21b BL5-12 CM7-22 BL2-21b BL3-4a BL4-3 BL5-4b 7.5 3.1 2.20 2.10 1.30 0.88 0.80 0.72 2.7 3.8 2.6 5.2 5.5 5.1 18.4 2.7 1.6 1.2 0.6 1.4 1.2 19.6 3.4 1.2 1.0 0.88 1.80 1.12 13 7.4 3.8 48.1 54.2 13.2 11.0 12.1 9.8 15.8 5.8 14.62 12.10 13.80 10.25 0.77 0.95 1.14 1.04 P-Al (mg L-1) 10 15 9.3 11.1 3.8 4.0 4.10 2.80 4.00 3.00 2.30 3.20 1.37 1.40 1.47 1.32 1.46 1.28 4.7 5.1 2.2 1.9 2.3 2.0 2.7 2.4 3.0 2.9 2.8 2.4 18.3 16.2 4.7 5.1 1.9 3.9 1.1 1.2 0.8 1.4 0.9 1.8 0.8 1.5 18.8 21.3 5.6 6.7 0.6 3.2 0.5 1.9 1.48 1.35 1.51 1.38 0.49 0.41 0.8 54.4 6.6 4.4 1.2 16.38 17.00 0.63 1.16 20 24.9 4.7 8.90 8.00 6.20 1.21 1.25 1.27 12.4 1.2 1.6 2.8 3.4 3.1 45.8 12.4 7.8 6.3 1.7 5.2 4.3 48.9 11.5 4.3 5.6 1.24 1.37 0.33 BL5-3 0.36 0.22 0.19 0.12 Selection of bacterial nitrogen fixer and phosphorus solubilizer for sweet potato The results of selection bacterial nitrogen fixer and phosphorus solubilizer from Al-P and Fe-P source for sweet potato from nitrogen fixer strains and 12 phosphorus solubilizer strains of endophytic and rhizopheric bacteria See in details, strains KG2-32, TG7-2-22 and HG7-2-12 produced 0.18 - 2.53, 9.94 - 13.73 and 7.59 - 11.88 mg L-1, respectively (Table 3.2) Table 3.2: Ability of nitrogen fixation and P solubilization from Al-P and Fe-P sources at pH 4.0 by selected endophytic rhizobacterial strains in sweet potato ASS area Long Xuyen Quadrangle Plain of Reed Depressed of Ha u River ASS area Long Xuyen Quadrangle Plain of Reed Days after incubation Strain KG2-32 KG9-211 AG1-111 AG9-31 TG7-2-22 LA2-33 LA1-33 LA2-113 HG7-2-12 VL9-42 VL5-211 HG5-32 Strain KG2-32 KG9-211 AG1-111 AG9-31 TG7-2-22 LA2-33 LA1-33 0.84 0.34 0.41 0.21 0.72 0.28 0.18 0.28 0.62 0.40 0.32 0.34 9.47 4.24 3.64 3.62 9.01 4.42 1.71 14 NH4+ (mg L-1) 1.09 2.15 0.23 0.39 0.30 0.34 0.24 0.28 0.82 1.73 0.31 0.48 0.20 0.23 0.26 0.26 0.77 1.49 0.52 0.26 0.29 0.29 0.38 0.36 P-Fe (mg L-1) 10 15 9.85 11.48 2.55 8.41 2.16 2.03 2.11 1.77 9.83 7.58 4.88 5.70 1.02 0.87 2.28 0.44 0.33 0.25 2.53 0.61 0.22 0.28 2.18 0.40 0.32 0.31 20 11.60 6.21 2.51 1.43 13.73 6.08 0.55 Depressed of Ha u River ASS area Long Xuyen Quadrangle Plain of Reed Depressed of Ha u River LA2-113 HG7-2-12 VL9-42 VL5-211 HG5-32 KG2-32 KG9-211 AG1-111 AG9-31 TG7-2-22 LA2-33 LA1-33 LA2-113 HG7-2-12 VL9-42 VL5-211 3.18 2.36 1.08 0.83 4.63 2.96 0.53 0.26 5.52 1.26 0.25 1.05 0.92 8.75 4.03 3.80 9.52 1.51 1.27 1.34 1.27 P-Al (mg L-1) 10 15 5.29 7.75 2.81 3.07 0.56 0.40 0.48 0.45 4.75 9.68 3.07 3.58 0.46 0.44 0.33 0.34 6.09 7.11 1.84 2.73 0.21 0.19 HG5-32 1.04 0.43 Strain 1.20 5.91 3.71 3.37 1.55 0.34 0.75 9.94 7.76 1.03 1.04 20 10.50 4.28 0.58 0.57 11.88 3.62 0.36 0.42 7.59 3.10 0.15 0.15 To obtain the maximum efficacy, one bacterium was selected for each area due to adaptive property of indigenous soil Thus, strains KG2-21, HG6-21band BL1-21b were selected for Long Xuyen Quadrangle, Depressed of Hau River and Plain of Reed, respectively They are the best strain for each area, with P concentration as 47.8, 98.5 and 88.8 mg L-1, respectively Moreover, all selected strains have ability of nitrogen fixation Particularly, strains HG6-21band BL1-21b also produced the highest NH4+ for each area Strains KG2-21, HG6-21b and BL1-21b were identified as Burkholderia vietnamiensis X1, Burkholderia vietnamiensis X2 and Burkholderia vietnamiensis X3, respectively Similarly, strains KG2-32, TG7-2-22, and HG7-2-12 were selected for sweet potato in Long Xuyen Quadrangle, Plain of Reed and Depressed of Hau River, respectively They were identified as Enterobacter cloacae X4, Burkholderia acidipaludis X5 and Bacillus sp X6 Strains KG2-32 and HG7-2-12 were selected because they are the best strain to fix nitrogen and also possess the 15 ability of P-solubilization in 15 highest strains For TG7-2-22, it belongs to acid-resistant bacterium that is a special property of ASS 3.2 Evaluation the effects of bacterial N-fixer and P solubilizer on rice and sweet potato yield 3.2.1 Effects of selected bacterial strains B vietnamiensis X1, X2, X3 and nitrogen fertilizer rates on rice yield in ASS in summerautumn 2015 The research results showed that the number of panicles per m and the number of filled grains per panicle were found to increase under the treatment of Burkholderia vietnamiensis X3 in 2015 SA season at Hong Dan and Long My districts As a result, the rice yield obtained from the Burkholderia vietnamiensis X3 bacterium treatment was highest among the three treated bacteria In Hon Dat district, however, the most efficiency was found in the soil treated with Burkholderia vietnamiensis X1 bacterium In 2015 AW season, the treatment of Burkholderia vietnamiensis X3 bacterium in combination with 60 kgN ha-1 brought about the rice yield higher than the treatment of 90 kgN ha-1 alone The research results indicated that application of phosphorus fertilizer alone to acid sulfate soils did not affect rice yields However, a combined application of phosphorus fertilizer and Burkholderia vietnamiensis X1 and Burkholderia vietnamiensis X3 bacteria resulted in the highest yield in Hon Dat district and Hon Dan district, respectively Table 3.3: Effects of selected bacterial strains and nitrogen fertilizer rates on rice yield components and yield in summer-autumn 2015 in acid sulfate soil Site Long My – Hau Gian g Factor Nitrogen rates (A) Treatmen t 30 N 60 N 90 N Grai n yield (ton ha-1) 5.45 b 6.41 a 6.52 Numbe r of panicle m-2 Total spikelet s panicle- 1.000 grain (g) Filled spikelet percentag e (%) 460b 89b 64.4b 23.6 510a 101a 70.6a 23.7 a a b 23.7 528 a 16 105 63.0 VK1 Tested bacteria(B ) VK2 VK3 F (A) F (B) F (A*B) CV (%) 30 N Nitrogen rates (A) 60 N 90 N Hon Dat – Kien Gian g VK1 Tested bacteria (B) VK2 VK3 F (A) F (B) F (A*B) CV (%) 30 N Nitrogen rates (A) 60 N 90 N Hong Dan – Bac Lieu VK1 Tested bacteria (B) VK2 VK3 F (A) F (B) F (A*B) CV (%) 6.02 481b 100 68.2 23.7 481b 96 66.9 23.8 537a 100 62.9 23.7 ** ** * 5.48 * ns ns 11.6 * ns ns 8.86 ns ns ns 7.24 372b 80.9b 79.1 25.8 473a 94.5a 84.4 25.7 478a 96.3a 76.4 25.2 476a 102a 81.1 25.8 422b 86.1b 82.1 25.7 426b 82.8b 76.7 25.3 ** * ns 9.66 ** ** ns 10.8 ns ns ns 8.74 ns ns ns 7.64 424b 97b 68.6 24.6 481a 106ab 70.9 23.3 494a 114a 71.1 24.1 460b 97b 69.2 23.6 444b 101b 72.1 23.9 a 494a 119a 69.3 24.3 ** ** * 6.16 ** ** ** 5.34 ** ** ns 9.32 ns ns ns 13.0 ns ns ns 6.04 b 5.89 b 6.53 a ** * * 6.99 3.95 b 4.76 a 4.81 a 4.89 a 4.21 b 4.41 b ** * ns 10.1 5.20 b 5.77 a 5.63 a 5.37 b 5.36 b 5.86 17 Values are means of four replications Different lowercase letters in the same column indicate significant differences at P