Influence of purple non-sulfur bacterial augmentation on soil nutrient dynamics and rice (Oryza sativa) growth in acidic saline-stressed environments.

The aim of the current study was to assess the potency of the exopolymeric substances (EPS)-secreting purple non-sulfur bacteria (PNSB) on rice plants on acidic salt-affected soil under greenhouse conditions. A two-factor experiment was conducted following a completely randomized block design. The first factor was the salinity of the irrigation, and the other factor was the application of the EPS producing PNSB (Luteovulum sphaeroides EPS18, EPS37, and EPS54), with four replicates. The result illustrated that irrigation of salt water at 3-4‰ resulted in an increase in the Na+ accumulation in soil, resulting in a lower rice grain yield by 12.9-22.2% in comparison with the 0‰ salinity case. Supplying the mixture of L. sphaeroides EPS18, EPS37, and EPS54 increased pH by 0.13, NH4+ by 2.30 mg NH4+ kg-1, and available P by 8.80 mg P kg-1, and decreased Na+ by 0.348 meq Na+ 100 g-1, resulting in improvements in N, P, and K uptake and reductions in Na uptake, in comparison with the treatment without bacteria. Thus, the treatments supplied with the mixture of L. sphaeroides EPS18, EPS37, and EPS54 resulted in greater yield by 27.7% than the control treatment.

Improving nitrogen content in soil and lemon balm (Melissa officinalis L.) yield by purple nonsulfur bacteria Rhodopseudomonas palustris in two consecutive seasons.

The study was conducted to assess the effects of nitrogen (N)-fixing purple nonsulfur bacteria (PNSB) Rhodopseudomonas palustris TLS06, VNW02, VNW64, and VNS89 on soil fertility, N uptake, essential oil (EO) content, growth, and yield of lemon balm. The experiment followed a completely randomized block design with 9 treatments and 3 replications. The treatments consisted of (i) applying 100% N as the recommended fertilizer rate (RFR), (ii) applying 85% N as RFR, (iii) applying 70% N as RFR, (iv) applying 55% N as RFR, (v) the treatment ii combined with N-PNSB, (vi) the treatment iii combined with N-PNSB, (vii) the treatment iv combined with N-PNSB, (viii) 0% as RFR combined with N-PNSB, and (ix) 0% N as RFR. The results showed that applying N-PNSB increased the plant height, and the number of primary branches in both seasons. In addition, the treatment without N fertilizer combined with N-PNSB increased stem leaf biomass by 41.2 and 50.3% in both seasons as compared with the treatment without neither N fertilizer nor N-PNSB. For soil properties, among treatments without N fertilizer, the treatment with N-PNSB increased concentrations of NH4+, soluble P, and exchangeable K+ by 41.3, 41.4, and 26.8%, respectively, as compared with the treatment without N-PNSB at the end of the second season. Applying 85% N as RFR combined with N-PNSB had a greater yield by 5.78-11.8% as compared with the treatment with 100% N as RFR, and a greater EO content by 23% as compared with the treatment with 85% N as RFR.

Yield gap reduction of pineapple (Ananas comosus L.) by site-specific nutrient management.

Acid-sulfate soils and overuse of chemical fertilizers have been obstacles to sustainable agriculture. The variation of fertilization due to poor soil fertility has remarkably affected the yield gap and the quality of the environment, so an optimal fertilizing rate should be formulated. Therefore, this study aimed at (i) detecting obstacles in soil characteristics reducing pineapple yield between farms and (ii) assessing the effects of NPKCaMg fertilizers on soil fertility, uptakes, and pineapple yield. The on-farm experiment was carried out according to site-specific nutrient management (SSNM) arranging in acid-sulfate soil for pineapple, including (i) no fertilizers used; (ii) NPKCaMg: fully fertilizing with nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg); (ii) PKCaMg: fertilizing without N; (iii) NKCaMg: fertilizing without P; (iv) NPCaMg: fertilizing without K; (v) NPKMg: fertilizing without Ca; (vi) NPKCa: fertilizing without Mg; and (vii) FFP: farmers' fertilizing practice. The result of the principal component analysis revealed that the soil had low availability of N, P, and K nutrients. Available P concentration was negatively correlated with concentrations of Al3+, Fe2+, and total Mn, whose correlation coefficients were -0.34 to -0.59, -0.52 to -0.74, and -0.63 to -0.70, respectively. Fertilizing NPKCaMg obtained the highest result in the uptakes of N, P, K, Ca, and Mg, which were 289.1-327.4, 25.4-29.3, 137.4-166.0, 41.9-48.9, and 39.8-43.1 kg ha-1, respectively. Fertilizing by SSNM has increased pineapple yield by 22.9 %-44.9 % compared to the FFP. This fertilizer formula should be transferred to the local farmers in order not only to enhance productivity, but also to limit the damage of chemical fertilizers on the environment. Moreover, this formula should be tested globally in other places that share similar soil characteristics.

The potency of a liquid biofertilizer containing bacterial strains of Rhodopseudomonas spp. on recovery of soil properties damaged by Al3+ and Fe2+ toxins and enhancement of rice yield in acid sulfate soil.

In the Mekong Delta Vietnam, rice is heavily affected by Al3+ and Fe2+ ions appearing in local acid sulfate soils (AAS). Therefore, the current study was carried out to assess the efficacy of a liquid biofertilizer (LB) containing nitrogen-fixing and phosphorus-solubilizing bacterial strains of Rhodopseudomonas spp. on remediation of soil characteristics and improvements of rice uptakes, growth, and yield. The experiment was designed in a randomized block design with nine treatments and four replications in an ASS. The results have shown that the LB application could contribute to the remediation of soil properties, including an increase in concentrations of NH4+ by 12.9%-19.4%, soluble P by 25.7%-42.6%, total N uptake by 40.7-64.0 kg ha-1 and total P uptake by 5.60-12.6 kg ha-1, and a decrease in concentrations of toxins, such as Al3+ by 12.1%-19.7% and Fe2+ by 16.6%-19.0%, compared to the treatment with the farmer-based fertilization. Thereby, grain yield was improved by 31.9%-32.2% with the LB versus the treatments without the bacteria and by 9.5%-11.1% compared to the commercial biofertilizer treatments. The application of LB reduced 25% N and 50% P of the recommendation versus the farmers' fertilization and improved performance of rice growth and yield cultivated on ASS which suffered from Al3+ and Fe2+ ions.

The current study has introduced the potential of the Rhodopseudomonas palustris TLS06, VNW02, VNW64, and VNS89 strains in performance as a bioremediator and a biofertilizer. The strains have shown their ability to recover acid sulfate soils, which had damaged the yield of rice plants due to high concentrations of Al³⁺ and Fe²⁺ ions. The work has delivered a biological approach to improve acid sulfate soil fertility and rice productivity in Vietnam and in other parts of the world, which have similar conditions, to achieve sustainable agriculture and food security.

Using Trichoderma asperellum to Antagonize Lasiodiplodia theobromae Causing Stem-End Rot Disease on Pomelo (Citrus maxima).

Stem-end rot disease has been causing damage to the production of pomelos in Vietnam. The cur-rent study aimed to (i) isolate fungal pathogens causing pomelo stem-end rot disease (PSERD) and (ii) discover Trichoderma spp. that had an antagonistic ability against pathogens under in vitro conditions. Fungi causing PSERD were isolated from pomelo fruits with symptoms of stem-end rot disease and collected from pomelo farms in Ben Tre province, Vietnam. Moreover, 50 fungal strains of Trichoderma spp. also originated from soils of these pomelo farms in Ben Tre province and were dual-tested with the fungal pathogen on the PDA medium. The results demonstrated that 11 pathogenic fungi causing PSERD were isolated from the fruit and showed mycelial growth of roughly 5.33-8.77 cm diameter at 72 h after inoculation. The two fungi that exhibited the fast-est growth, namely, S-P06 and S-P07, were selected. ITS sequencing of the S-P06 and S-P07 fungi resulted in Lasiodiplodia theobromae. All the 50 Trichoderma spp. strains were allowed to antago-nize against the S-P06 and S-P07 strains under in vitro conditions. The greatest antagonistic effi-ciency was found in Trichoderma spp. T-SP19 at 85.4-86.2% and T-SP32 at 84.7-85.4%. The two antagonists were identified as Trichoderma asperellum T-SP19 and T-SP32. The selected strains of Trichoderma asperellum were potent as a biological control for fruit plants.

Isolation and characterization of novel potassium-solubilizing purple nonsulfur bacteria from acidic paddy soils using culture-dependent and culture-independent techniques.

The current research as aimed (i) to isolate and select the purple nonsulfur bacteria (PNSB) possessing the potassium-solubilizing ability from acid paddy fields and (ii) to evaluate the ability to release the plant growth-promoting substances (PGPS) of selected PNSB. A total of 35 acid sulfate (AS) soil samples were collected in An Giang province, Vietnam. Then, 70 PNSB strains were isolated from the AS soil samples. In the current study, the isolated strains were screened and selected according to their tolerability to acidic conditions, ability to solubilize potassium, and characteristics of a plant growth promoter on basic isolation media with various incubation conditions. Therein, three strains, TT07.4, AN05.1, and AC04.1, presented the highest potassium solubilization under the microaerobic light (11.8-17.7 mg L-1) and aerobic dark (16.4-24.7 mg L-1) conditions and stresses from Al3+, Fe2+, and Mn2+ toxicity. The selected strains were identified as Rhodopseudomonas pentothenatexigens by the 16S rDNA sequence, with 99% similarity. The selected acidic-resistant strains possessed the traits of biofertilizers under both microaerobic light and aerobic dark conditions, with abilities to fix nitrogen (0.17-6.24; 7.93-11.2 mg L-1); solubilize phosphorus from insoluble compounds with 3.22-49.9 and 9.49-11.2 mg L-1 for Al-P, 21.9-25.8 and 20.2-25.1 mg L-1 for Ca-P, and 10.1-29.8 and 18.9-23.2 mg L-1 for Fe-P; produce 5-aminolevulinic acid (0.63-3.01; 1.19-6.39 mg L-1), exopolymeric substances (0.14-0.76; 0.21-0.86 mg L-1), indole-3-acetic acid (12.9-32.6; 13.6-17.8 mg L-1), and siderophores (28.4-30.3; 6.15-10.3%). The selected potassium-solubilizing strains have a great potential to apply in liquid form into rice seed and solid form in AS soils to supply nutrients and PGPS for enhancing rice growth and grain yield.

Improvement of Nutrient Uptake, Yield of Black Sesame (Sesamum indicum L.), and Alluvial Soil Fertility in Dyke by Spent Rice Straw from Mushroom Cultivation as Biofertilizer Containing Potent Strains of Rhodopseudomonas palustris.

The aim of the current research was to evaluate the effects of members of purple nonsulfur bacteria (PNSB), Rhodopseudomonas palustris strains of VNW02, TLS06, VNW64, and VNS89, mixed with spent rice straw (SRS) from mushroom cultivation as a carrier on promoting sesame growth and yield, and ameliorating the alluvial soil (AS) fertility in dykes. A 4 × 3 factorial experiment consisting of different levels of the solid PNSB biofertilizer mixture at 0, 3, 4, and 5 t·ha-1 (0, 1.81 × 108, 2.24 × 108, and 2.68 × 108 cells pot-1, respectively), and nitrogen (N) and phosphorus (P) inorganic fertilizer rates (100, 75, and 50 kg·N·ha-1; 60, 45, and 30 kg P2O5·ha-1, respectively) was performed in pots with the sesame variety of ADB1 in the dyked AS. The solid PNSB biofertilizer mixture at at least 3 t·ha-1 significantly enhanced the sesame seed yield by providing higher macronutrients for plants by increasing available N and soluble P concentrations in the soil. The solid PNSB biofertilizer mixture in addition to 75% of the recommended N and P fertilizers produced an equivalent yield in comparison to the utilized 100% of N and P inorganic fertilizers. The solid PNSB biofertilizer mixture in the SRS from the mushroom production reduced at least 25% of N and P chemical fertilizers for gaining the maximal seed yield and enriched soil characteristics for the sustainable black sesame cultivation in the dyked AS.