Vermicompost is a promising amendment for immobilization of cadmium (Cd) in soils; however, its effectiveness can be influenced by rhizosphere environment conditions, such as pH and the presence of low-molecular-weight organic acids (LMWOAs). In this study, a batch experiment was conducted to examine the characteristics of Cd adsorption by vermicompost at different pH (pH = 3, 5, and 7) and after the addition of different LMWOAs (oxalic acid; citric acid; malic acid). Furthermore, a series of morphology and structural analyses were conducted to elucidate the mechanisms of observed effects. The results showed that the adsorption capacity of vermicompost for Cd increased as pH increased, and chemisorption dominated the adsorption process. Changes in pH altered adsorption performance by affecting the -OH groups of alcohol/phenol and the -CH₂ groups of aliphatics. Further, the addition of oxalic acid promoted Cd adsorption, and the effect was concentration dependent. Modifying the verimicompost surface with more adsorption sites might be the main reason. Conversely, citric acid and malic acid showed the ability to inhibit Cd adsorption by vermicompost. Citric acid caused a blocking effect by covering flocculent substances on the vermicompost surface while reducing surface adsorption sites by dissolving mineral components such as iron oxides. However, the action of malic acid did not appear to be related to changes in morphology or the structure of vermicompost. Overall, the results of this study partially explain the limited effectiveness of Cd immobilization within the rhizosphere by vermicompost, and provide theoretical support for regulating rhizosphere environments to improve the effectiveness of vermicompost immobilization of Cd.

Brown rot disease caused by Pyrrhoderma noxium is a widespread disease that severely affects the roots of rubber trees (Hevea brasiliensis Muell. Arg.). The economic losses, along with environmental and health problems arising from the use of disease control chemicals, have raised the interest of scholars to explore the use of biological control agents for the effective control of fungal pathogen P. noxium. Here, the inhibition effect of the culture filtrate of B. subtilis Czk1 on P. noxium was demonstrated. The findings indicate that the antifungal activity of this strain is mediated wholly or partly by compounds produced in the culture filtrate. The combined use of liquid chromatography–tandem mass spectrometry and antifungal activity assays rapidly identified compounds produced by B. subtilis Czk1. Metabolic profiles were assessed and used to identify major metabolites based on the scores of variable importance in the projection and the plot scores of principal component analysis. A total of 296 differential metabolites were screened, including 208 in positive ion mode and 88 in negative ion mode. Two key metabolites, diacetyl and trans-2-octenoic acid, were screened from 29 metabolites by antifungal activity assays. The median effective concentration (EC₅₀) of trans-2-octenoic acid and diacetyl were 0.9075 mg/mL and 4.8213 mg/mL, respectively. The antifungal metabolites can disrupt the internal structure of the pathogenic fungal mycelium, thereby impeding its growth. This study is expected to contribute to the existing knowledge of Czk1-produced metabolites and their future antifungal applications. This study is also expected to provide a new biopreservative perspective on unexplored antifungal metabolites produced by Czk1 as a biocontrol agent.

Sisal purple leafroll disease (SPLD) is currently the most destructive disease affecting sisal in China, yet its aetiology remains unclear. In our previous research, it was verified to be associated with phytoplasmas, and nested PCR based on the 16S rRNA gene using universal primers R16mF2/R16mR1 followed by R16F2n/R16R2 was confirmed as the most effective molecular method for the detection of phytoplasmas associated with SPLD (SPLDaP). However, the method has a shortcoming of inaccuracy, for it could produce false positive results. To further manage the disease, accurate detection is needed. In this study, we developed a specific nested PCR assay using universal primers R16F2n/R16R2, followed by a set of primers designed on 16Sr gene sequences amplified from SPLDaP, nontarget bacteria from sisal plants, and other phytoplasma subgroups or groups. This established method is accurate, specific, and effective for detection of 16SrI group phytoplasma in sisal, and its sensitivity is up to 10 fg/μL of total DNA. It also minimized the false positive problem of nested PCR using universal primers R16mF2/R16mR1 followed by R16F2n/R16R2. This method was further used to verify the presence of phytoplasma in Dysmicoccusneobrevipes, and the results showed that D. neobrevipes could be infected by SPLDaP and thus could be a candidate for vector transmission assays.

Sugarcane brown rust (SCBR), caused by Puccinia melanocephala, is a destructive fungal disease that has extensively spread in the sugarcane-cultivating regions across the world. Early monitoring plays an important role in predicting the P. melanocephala epidemic and managing SCBR. However, accurately identifying SCBR based on symptoms and urediniospore morphology at the initial stage is a challenge. Further, it is tedious, time-consuming, labor-intensive, and requires expensive equipment to detect P. melanocephala using PCR-based methods. Loop-mediated isothermal amplification (LAMP) technology is renowned for its speed, simplicity, and low equipment requirements for specifically and sensitively identifying many pathogens. Therefore, in this study, a novel and highly sensitive LAMP assay was developed for the specific detection of P. melanocephala in sugarcane. Here, the internal transcribed spacer (ITS) sequence of P. melanocephala was selected as the target gene for LAMP primer design. Based on the color change of SYBR Green I and gel electrophoresis, specific LAMP primers were screened. Further, the optimal reaction conditions for the LAMP assay were determined at 63 °C for 60 min. The LAMP assay showed a high degree of specificity for the detection of P. melanocephala in sugarcane, with no cross-reactivity with other fungal pathogens. The established LAMP protocol was highly sensitive and can be used to detect as low as 1 pg/μL of P. melanocephala plasmid DNA, which is comparable to that of nested PCR and ~100 times more sensitive than conventional PCR. Finally, the detection rate of the LAMP method was higher than that of conventional and nested PCR in field samples.

Sisal is an important tropical cash crop in southern China. Unfortunately, it is threatened by various diseases. In 2022, a new disease tentatively named marginal leaf blight disease (MLBD) was first observed in sisal fields across Guangxi and Guangdong provinces, with an incidence rate ranging from 13% to 30%. In this work, to isolate and identify the pathogens causing MLBD, sisal leaves exhibiting the typical MLBD symptoms were collected, and nine strains were obtained. Pathogenicity tests, morphological observations, and phylogenetic analyses confirmed that two strains, namely 22GX1-3 and 22GD1-4, identified as Phaeosphaeriopsis obtusispora, were the causative pathogens of MLBD. Further investigations into the biological characteristics of P. obtusispora showed that its mycelia exhibited optimal growth on PDA medium, with the most favourable temperature and pH being 25 °C and 7.0, respectively. The mycelia could grow in temperatures ranging from 10 °C to 32 °C but ceased at 35 °C. Lactose and yeast extract powder were also identified as the optimal carbon and nitrogen sources, respectively. Additionally, the effectiveness of various control agents was assessed on a single strain, 22GX1-3. Among the twelve fungicides tested, difenoconazole was proven the most effective, with an EC₅₀ value of 0.5045 µg/mL. To our knowledge, this is the first report for sisal MLBD caused by P. obtusispora. Our results provide crucial pieces of information for the development of effective management strategies to control sisal MLBD caused by P. obtusispora.

Large-scale tropical forest conversion to plantations or cropland severely impacts soil health. However, most studies have relied on pairwise designs, single-type chronosequences, or multi-type comparisons that are often confounded by environmental heterogeneity, thereby overlooking the complexity of successive land-use transitions on a common land-use background. Here, we investigated the responses of soil physicochemical properties and microbial communities to two conversion pathways (NSF → ORF → YRF; NSF → ORF → URF → AL) within a single farm, where shared soil parent material and climate allowed for a direct comparison of land-use types with different conversion pathways. Soil properties and microbial diversity were analyzed using physicochemical methods and high-throughput sequencing, with samples collected from five land-use types (six biological replicates per type). Results showed NSF had the highest soil properties. Along NSF → ORF → YRF, TOC, DOC, TN, IN and C/N declined gradually. In contrast, URF exhibited severe degradation, with AL showing partial recovery. Bacterial diversity remained relatively stable, whereas fungal communities were highly sensitive, with diversity decreasing progressively and dominant phyla shifting with intensified disturbance. DOC, EC and SM were most strongly associated with microbial community ordination, with pH showing no significant association. URF had the highest predicted abundance of C/N/S cycling genes, while NSF maintained a balanced fungal trophic structure. This study provides a comparative assessment of soil properties and microbial communities along two tropical land-use conversion pathways, contributing empirical evidence for sustainable land-use management in tropical regions.