Nguyen Duc Trong

In lowland rice cultivation, climate change is increasingly intensified by rising greenhouse gas emissions, especially methane (CH ₄ ). This study aimed to: (i) isolate and select acid sulfate-tolerant purple nonsulfur bacteria (PNSB) capable of nutrient provision; and (ii) screen and identify PNSB strains that reduce CH ₄ emissions. A total of 60 soil and 60 water samples were collected from four acid sulfate rice-growing areas in the Mekong Delta, Vietnam. From these, 118 PNSB strains were isolated, and 100 were selected based on their acid-sulfate tolerance, nitrogen fixation, phosphate solubilization, and indole-3-acetic acid (IAA) production. Among them, strains WHA-1A, WHA-9B, and SPL-4A exhibited the greatest CH ₄ emission reduction under both microaerobic light (17.1–61.3%) and aerobic dark (48.2–75.2%) conditions. These strains also demonstrated nitrogen fixation (21.5–22.9 and 19.4–31.4 mg L ^− 1 ), solubilization of three insoluble phosphate forms—Fe-P, Al-P, and Ca-P for both conditions (21.9–29.6 and 11.9–14.8 mg L ^− 1 ; 8.12–15.1 and 19.0–30.2 mg L ^− 1 ; 12.5–27.0 and 18.5–31.4 mg L ^− 1 , respectively), and IAA production (0.34–1.91 and 2.24–6.28 mg L ^− 1 ). Based on 16S rRNA gene sequencing, two strains WHA-1A and SPL-4A were identified as Rhodobacter sphaeroides , and WHA-9B was identified as Blastochloris sulfoviridis . These strains show promise for mitigating CH ₄ emissions and improving rice growth in acid sulfate soils.

Fruit rot disease is a major obstacle for starapple production in Vietnam. Therefore, the aims of the current study were (i) to identify the causing agents for fruit rot in starapple, (ii) to select isolates of Trichoderma spp. as antagonists, and (iii) to determine efficient approaches to control the disease. The pathogens were isolated from symptomatic starapple fruits collected in Can Tho City, Vietnam. The antagonists were isolated from the soils of healthy starapple farms. The three pathogenic isolates with the fastest growth (20.5–45.0 mm) and the largest infection spot (14.5–16.5 mm) were Calonectria candelabra C-SA01, C. candelabra C-SA06, and C. sulawesiensis C-SA07. Four Trichoderma isolates, T-SA01, T-SA06, T-SA10, and T-SA14, were selected because they consistently showed high antagonistic efficiency against C-SA01, C-SA06, and C-SA07 in dual-culture assays at 56.7–69.5%, 50.4–70.8%, and 62.6–69.2%, respectively. ITS-based results tentatively assigned T-SA01 to T. harzianum and T-SA06, T-SA10, and T-SA14 to T. asperellum. Under in vivo conditions, each Trichoderma sp. isolate was combined with different spraying methods. The result revealed that the four antagonists showed identical outcomes in reducing fruit rot disease. Spraying Trichoderma spp. both one day before and after inoculation resulted in the best biocontrol, with the highest disease-reducing rate at 44.2% at day 5. These newly found antagonists should be further tested in actual starapple farms to reveal their true potency.

Diseases caused by Fusarium spp. vary around the world. It is important to determine the causals agents and indigenous antagonists against these pathogens. Thus, this study aimed to (i) determine the pathogens of root rot and yellow leaf disease (RRYLD), (ii) select Trichoderma spp. strains to control the pathogens, and (iii) evaluate methods for preparing the antagonistic fungi. Diseased soil samples were collected from pomelo orchards in Ben Tre province, Vietnam. The experiment isolated 08 Fusarium spp. strains, with the fastest growth in PDA in FP-C16, FP-B18, FP-B16, and FP-B03 (8.33–17.3 mm) on day 4 of culture. They were identified as Fusarium fujikuroi FP-C16, F. verticillioides FP-B18, F. verticillioides FP-B16, and F. incarnatum FP-B03. On the other hand, 25 Trichoderma spp. strains were isolated from the pomelo rhizosphere. Among them, 13 Trichoderma spp. strains showed rapid growth and strong antagonistic activity against two Fusarium spp. strains under laboratory conditions. The two Trichoderma spp. strains TP-C40 and TP-G50 had antagonistic efficiencies against FP-C16 and FP-B16 at 47.7–63.5%. The two selected Trichoderma spp. strains were identified as Trichoderma asperellum TP-C40 and T. yunnanense TP-G50. The two Trichoderma spp. strains TP-C40 and TP-G50 reduced the number of leaves and roots infected by Fusarium spp.

Background: Potassium (K) is a key limiting nutrient in most soils due to soil characteristics. Hence, biological K solubilization may be a potential tool for enhancing the availability of native K and thereby plant growth. The present study evaluated the potassium-solubilizing (K-sol) capacity from insoluble K minerals by strains of K-solublizing purple non-sulfur bacteria (PNSB) Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11 and Rhodospeudomonas palustris M-So-14 isolated from alluvial soil. Methods: The experiment was conducted in a completely randomized design in the laboratory with six treatments: (i) no soil and no PNSB, (ii) soil but no PNSB (iii) soil with a single strain of M-Sl-09, (iv) soil with a single strain of M-So-11, (v) soil with a single strain of M-So-14 and (vi) soil with mixture of K solubilizer. Result: The results revealed that the exchangeable K content (exK) in M-Sl-09, M-So-14, or mixed treatments were greater than those ofM-So-11 (2.35-2.42 greater than 2.19 meq 100 g-1) and bottomed in the treatment without soil nor PNSB (0.093 meq 100 g-1) at 10 days after PNSB inoculation. Furthermore, the cation exchange capacity of treatments with PNSB was 11.0-15.4% greater than those without PNSB. Likewise, optical density of PNSB in treatments with PNSB were greater than those without PNSB with turbidity of 2.14-2.44 greater than 1.02, respectively.

The increasing reliance on chemical fertilizers has raised environmental concerns and highlighted the need for sustainable alternatives. This study aimed to (i) optimize the carrier-to-substrate ratios and moisture content during composting with potassium-solubilizing purple nonsulfur bacteria (K-PNSB) and (ii) evaluate the growth-promoting effect of the optimized biofertilizer on maize seedlings. Three K-PNSB strains (Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11, and Rhodopseudomonas palustris M-So-14) were used. Composting experiments were conducted using different carrier-to-substrate ratios and moisture levels with K-PNSB inoculation. Compost quality was assessed through nutrient dynamics, bacterial density, and physicochemical properties over four weeks. The results showed that the 1:1:3 substrate ratio combined with 50–60% moisture content consistently enhanced K solubilization, bacterial survival, and compost maturity indicators. Application of the optimized biofertilizer improved maize growth traits compared with the non-inoculated control. These findings demonstrate that controlling material ratios and moisture content improves compost quality and plant growth performance, providing a sustainable alternative to chemical fertilizers. This study provides a practical framework for developing sustainable K-solubilizing biofertilizers from agricultural residues.

Mục tiêu của nghiên cứu này là đánh giá ảnh hưởng của vi khuẩn quang dưỡng không lưu huỳnh màu tía (PNSB) cố định đạm (N) đến sinh trưởng và năng suất lúa vụ Hè Thu năm 2023 trồng trên một số nền đất nhiễm mặn lúa - tôm của Châu Thành - Trà Vinh, Mỹ Xuyên - Sóc Trăng, Thới Bình - Cà Mau và An Biên - Kiên Giang trong điều kiện nhà lưới. Thí nghiệm 2 nhân tố được bố trí theo khối hoàn toàn ngẫu nhiên. Trong đó, nhân tố A là bốn mức bón phân N (100, 75, 50, 0% N theo công thức khuyến cáo 100N-60P2O5-30K2O) và nhân tố B là PNSB cố định N, Rhodobacter sphaeroides (không bổ sung vi khuẩn, bổ sung dòng đơn R. sphaeroides S01, dòng đơn R. sphaeroides S06 và hỗn hợp hai dòng vi khuẩn R. sphaeroides S01 và S06), với 4 lần lặp lại, mỗi lần lặp lại 8 cây/chậu. Kết quả cho thấy việc bổ sung vi khuẩn R. sphaeroides S01, S06 đã cải thiện chiều cao cây lúa (2,60 - 24,3%), chiều dài bông (4,42 - 14,3%), số bông/chậu (7,48 - 25,4%), số hạt chắc/bông (3,11 - 40,4%), tỷ lệ hạt chắc (0,68 - 23,6%) và năng suất hạt lúa (7,03 - 69,9%) trên nền đất của 4 vùng nghiên cứu.

This study was conducted to evaluate the effects of liquid purple nonsulfur bacteria capable of solubilizing potassium from muscovite (MS‐PNSB) on soil properties, potassium uptake, growth, and yield of hybrid maize under greenhouse conditions. A two‐factor experiment was arranged in a completely randomized block design with 25 treatment combinations. Factor A consisted of five bacterial treatments (no bacteria, single strain M‐Wa‐19, M‐Wa‐24, and M‐Wa‐26, and a mixture of the three strains), and factor B consisted of K fertilizer application rates (0%, 25%, 50%, 75%, and 100% of the recommended rate). The results showed that MS‐PNSB application improved soil pH _H2O and reduced electrical conductivity (EC) and exchangeable Na by 4.74%–7.97%, 7.17%–27.5%, and 4.92%–18.5%, respectively. In addition, available soil nutrients increased, including NH ₄ ⁺ ‐N (9.96%–33.8%), NO ₃ ^- ‐N (33.1%–42.8%), soluble P ₂ O ₅ (28.8%–34.6%), and exchangeable K ⁺ (41.4%–79.3%). Consequently, total K uptake by maize plants increased by 16.3%–51.4% compared with the noninoculated control. Reducing K fertilizer rates resulted in proportional decreases in total plant K uptake, following the order 100% > 75% > 50% > 25% > 0% K, corresponding to 1894.6, 1812.2, 1702.6, 1598.0, and 1426.6 mg pot ⁻¹ , respectively. Moreover, inoculation with the MS‐PNSB mixture significantly improved plant height (7.64%), ear length (5.78%), ear diameter (9.48%), and number of kernels per row (9.25%) compared with the noninoculated treatment. Application of single strains M‐Wa‐19 or M‐Wa‐26, or the three‐strain mixture combined with reduced K fertilization, achieved yields comparable to the treatment receiving 100% chemical K fertilizer alone, indicating that sole application of chemical K fertilizer did not produce the highest yield and that MS‐PNSB supplementation has strong potential to enhance maize productivity.

This study was conducted to evaluate the effects of solid biofertilizer (SBF) containing potassium-solubilizing purple nonsulfur bacteria (K-PNSB), including Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11, and Rhodopseudomonas palustris M-So-14, on soil properties, K uptake, growth, and yield of hybrid maize cultivated in dyked alluvial soil collected from an Phu, An Giang. A two-factor experiment was arranged in a completely randomized design with four replications. The first factor was K fertilizer levels (0, 25, 50, 75, and 100 % of the recommended rate), and the second was SBF types (sterile water only, single strains M-Sl-09, M-So-11, M-So-14, or a mixture of all three strains). The application of SBF containing either single or mixed K-PNSB strains significantly enhanced soil exchangeable K, total K uptake, plant growth, and grain yield compared with the uninoculated control. The highest yield and total K uptake were recorded under 100 % K fertilizer combined with the three-strain SBF (106.5 g plant ⁻¹ ), demonstrating a strong synergistic interaction between biofertilizer and K application. These findings suggest that K-PNSB-based biofertilizer can improve potassium availability and maize productivity in nutrient-depleted dyked alluvial soils.

Potassium (K) is a vital macronutrient for plant growth and yield, yet most soil K occurs in insoluble mineral forms, limiting availability to crops. Reliance on chemical K fertilizers is unsustainable due to cost and environmental concerns. Microbial solubilization of mineral K, particularly by purple nonsulfur bacteria (PNSB), offers an eco-friendly alternative. This study focused on isolating mica-potassium-solubilizing purple nonsulfur bacteria (MK-PNSB) from in-dyke alluvial soil and assessing their effects on hybrid maize germination and seedling growth. Among the isolates, the results showed that strain M-Wa-19 released the highest amount of soluble K under microaerobic light conditions (27.4 mg∙L⁻¹). Under aerobic dark conditions, M-Wa-24 and M-Wa-26 released 20.1–21.0 mg∙L⁻¹ of soluble K. Strains M-Wa-21, M-Wa-25, and M-Sl-13 solubilized K in the range of 14.3–25.1 mg∙L⁻¹ and 12.9–24.4 mg∙L⁻¹ under both incubation conditions. The selected strains were identified by 16S rRNA as Rhodopseudomonas palustris strain M-Sl-13 (PX588604), Rhodoplanes pokkaliisoli strain M-Wa-19 (PX588605), Afifella marina strain M-Wa-21 (PX588606), Rhodocista pekingensis strain M-Wa-24 (PX588607), Rhodocista pekingensis strain M-Wa-25 (PX588608), and Rhodocista pekingensis strain M-Wa-26 (PX588609). None exhibited toxicity to maize seeds; instead, all enhanced seed vigor indices by up to 99.7% and improved plant height and root biomass by 19.0–26.2% and 14.4–22.9%, respectively, under static hydroponic conditions. At a 1:1000 (bacteria and distilled water) dilution rate, strains M-Wa-26, M-Wa-25, M-Sl-13, M-Wa-24, M-Wa-19, and M-Wa-21, along with the six-strain mixture, improved seed vigor index by 3.96–7.91%. These findings suggest that MK-PNSB, individually or in mixtures, hold promise as biofertilizer candidates for sustainable K management in crop production.