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.

Biogas digestive effluent (BDE) is a nutrient-enriched source that can be utilized as an organic fertilizer for rice cultivation without synthetic fertilizer (SF) application. However, a primary concern is the stimulation of methane (CH₄) emissions due to the enrichment of the labile organic carbon, a favorite substrate of methanogenic archaea. Methanotrophs potentially reduce greenhouse gas (GHG) emissions from rice fields owing to metabolizing CH₄ as a carbon source and energy. We therefore examined the effect of the application of methanotroph-inoculated BDE to the rice cultivated paddy soil on GHG emissions and rice productivity under a pot experiment. Methanotrophs (Methylosinus sp. and Methylocystis sp.), isolated from the Vietnamese Mekong Delta’s rice fields, were separately inoculated to the heated BDE, followed by a 5-day preincubation. Methanotroph-inoculated BDE was supplied to rice cultivation to substitute SF at 50% or 100% in terms of nitrogen amount. The results showed that the total CH₄ emissions increased ~34% with the application of BDE. CH₄ emissions were significantly reduced by ~17–21% and ~28–44% under the application of methanotroph-inoculated BDE at 100% and 50%, respectively. The reduction in CH₄ was commensurate with the augmentation of pmoA transcript copy number under methanotroph-inoculated BDE. In addition, methanotroph-inoculated BDE application did not increase nitrous oxide (N₂O) emissions and adversely affect rice growth and grain productivity. This study highlighted the BDE-recirculated feasibility for a lower CH₄ emission rice production based on methanotrophs where high CH₄-emitting fields were confirmed.

Different rice farming systems affect the soil microbial communities. Here, we report the results of 16S rRNA gene amplicon sequencing of soils collected from intensive rice cultivation and rice-shrimp farming systems in Soc Trang, Vietnam. The dominant phyla in these systems were Firmicutes , Actinobacteriota , Chloroflexi , Myxococcota , and Acidobacteriota .

Fruit rot seriously damages pomelo production. Given concerns regarding the safety of chemical agents, biological alternatives are becoming more preferable. Therefore, the experiment aimed to (i) identify the pathogens causing pomelo fruit rot disease and (ii) select Trichoderma spp. strains controlling the determined pathogens in Ben Tre, Vietnam. Three pathogenic fungal strains isolated from diseased pomelo fruits were selected. The three pathogenic fungal strains were randomly injected into 9 healthy pomelo fruits. The strain PCP-B02-A2 led to a completely rotten fruit on day 17 after infection, while strains PCP-B02-B2 and PCP-B03-A1 had infected spots whose lengths were 17.5 and 28.1 mm, became larger, and eventually led to the whole fruit rot. The pathogens were identified by the internal transcribed spacer (ITS) technique as Colletotrichum gloeosporioides PCP-B02-A2, Pseudopestalotiopsis camelliae sinensis PCP-B03-A1, and P. chinensis PCP-B02-B2. Twenty-five Trichoderma spp. strains were isolated. The ITS technique identified four strains, including Trichoderma asperellum TP-B01, T. harzianum TP-B08, T. harzianum TP-B09, and T. asperellum TP-C25. The PCP-B02-A2 strain had antagonism at 66.7–68.7%, while those of PCP-B02-B2 and PCP-B03-A1 were 64.2–71.1% and 55.7–57.4%, respectively.

Phosphorus (P) is an important element in crop production. However, under climate change, salinization and acidification limit soil P availability and crop yield, especially rice, while the application of chemical P fertilizer causes an adverse effect on the environment. Thus, the study aimed at assessing the effectiveness of strains of purple nonsulfur bacteria (PNSB) that can solubilize P and tolerate salinity (PNSB-P) in reducing Na+ in soil and plant and improving P uptake, growth, and yield of rice in salinized soils in Vietnam. An experiment with two factors was arranged in completely randomized blocks and replicated four times under greenhouse conditions. Therein, the first factor was five levels of P fertilizers: 0 %, 25 %, 50 %, 75 %, and 100 % of the local recommended level. The second factor was the PNSB-P including single strains of Cereibacter sphaeroides ST16 and ST26, the mixed strains of both C. sphaeroides ST16 and ST26, and the negative control. The results showed that utilizing C. sphaeroides ST16 and ST26 decreased plant proline content by 2.46–6.70 µmol g-1 and soil Na+ concentration by 1.47–1.62 meq 100 g-1. Utilizing PNSB-P increased P content by 5.82–29.2 % in stem-leaf and 12.1–14.6 % in rice grain and decreased 15.1–16.4 % of Na content in stem-leaf and 8.00–15.1 % in rice grain. Moreover, utilizing PNSB-P improved soluble P content by 4.33–9.07 mg P kg-1 and total P uptake by 24.0–46.6 % compared with the negative control. The C. sphaeroides bacteria not only increased rice yield components such as the number of panicles per pot, the number of rice grains per panicle, and filled rice grain rate but also enhanced 20.7–47.6 % of rice grain yield compared with the negative control. Noticeably, utilizing mixed bacterial strains decreased 100 % of chemical P fertilizer compared with the recommendation.