Introduction: The biocontrol strain Pseudomonas aeruginosa 8-7 (PA8-7) produces antimicrobial metabolites, yet its application is limited by low yield and insufficiently characterized environmental stability. Methods: Fermentation was optimized through medium screening, single-factor experiments, and orthogonal array design. The resulting cell‑free filtrate (CFF) was evaluated for antifungal activity against 19 tropical crop pathogens, environmental stability (thermal, pH, UV, reductants, metal ions), rhamnolipid composition (TLC, HPLC‑MS, ¹H NMR), field efficacy against rubber tree powdery mildew ( Oidium heveae ), and biosafety on soybean seedlings. Results: The optimal medium (15 g/L acid‑hydrolyzed casein, 25 mL/L glycerol, 1 g/L MgSO₄·7H₂O, 1.5 g/L K₂HPO₄, pH 6.5) and culture conditions (50 mL/500 mL flask, 220 rpm, 10% inoculum, 36 °C, 5 days) increased antifungal activity against Colletotrichum alienum by 54% to 89.81%. The CFF exhibited broad‑spectrum activity against all 19 pathogens, with the highest inhibition against Phytophthora litchii (94.56 ± 1.38%) and Phytophthora melonis (93.87 ± 1.69%). It retained >87% activity after autoclaving (121 °C, 30 min), remained stable across pH 1–12, and tolerated UV, reductants and most metal ions. Eighteen rhamnolipid congeners (9 mono‑, 9 di‑) were identified. Field trials showed that a 10‑fold diluted CFF reduced the disease index of rubber tree powdery mildew from 23.55 to 21.11 within 7 days (73.23% control efficacy), with no phytotoxicity on soybean seedlings. Conclusion: The optimized CFF combines broad‑spectrum activity, exceptional stability, and field efficacy with biosafety, making it a promising low‑cost biocontrol candidate for sustainable tropical agriculture.

Rubber tree powdery mildew caused by Erysiphe quercicola is the most widespread and destructive foliar disease in China’s rubber-growing regions. This disease frequently occurs in severe epidemics during winter–spring each year, delaying rubber tapping by 1–2 months and causing substantial yield losses, and has become a critical bottleneck for stable natural-rubber production. Xishuangbanna is China’s core planting region for natural rubber and a typical representative of mountainous rubber plantations in Yunnan. More than two-thirds of local rubber plantations are located on mountain slopes steeper than 15°. However, the population-genetic background of E. quercicola in this region remains poorly understood. A total of 188 samples of rubber powdery mildew were recovered from nine sampling sites belonging to three geographic populations (Mengla, Menghai, Jinghong). Ten SSR loci were used to analyse the genetic diversity, genetic differentiation and population structure of the tested samples. The results revealed that E. quercicola in Xishuangbanna rubber plantations exhibited high overall genetic diversity. Most samples possessed unique genotypes even at a fine spatial scale, and the Mengla population showed higher genetic diversity than the other populations. Analysis of molecular variance (AMOVA) revealed that the genetic variation of E. quercicola in Xishuangbanna was predominantly partitioned within sampling-site subpopulations. Significant pairwise genetic differentiation was detected among the three geographic populations, although all pairwise ΦPT values were less than 0.1, indicating a pattern of significant yet limited genetic differentiation at fine geographic scales. PCoA and STRUCTURE analyses further confirmed obvious population genetic structure in this region. The results of this study provide a theoretical basis for the epidemic monitoring of rubber powdery mildew in the Xishuangbanna rubber plantation area.

Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg., the world’s primary source of natural rubber, faces increasing threats from emerging diseases in tropical cultivation regions. During recent field surveys in Yunnan and Hainan provinces of China, previously uncharacterized brown, water-soaked necrotic lesions were observed on tender stems and leaves of rubber trees. This study aimed to identify the causal pathogen, characterize its biological traits, and evaluate candidate fungicides for disease management. The pathogen was isolated via tissue explant methods and identified through morphological observation combined with multigene phylogenetic analyses based on the internal transcribed spacer (ITS) region, large subunit (LSU) ribosomal DNA, and cytochrome c oxidase subunits I and II (coxI and coxII) sequences. Pathogenicity was rigorously confirmed by fulfilling Koch’s postulates on rubber tree seedlings. The isolates produced spherical to ovoid, papillate sporangia, and phylogenetic reconstruction strongly supported clustering them with Phytopythium vexans. The pathogen grew optimally at 16–31 °C, with growth ceasing at 35 °C. Fungicide sensitivity assays revealed that metalaxyl exhibited the strongest inhibitory activity against mycelial growth, with half-maximal effective concentration (EC₅₀) values as low as 0.04 μg/mL. To our knowledge, this is the first report of P. vexans causing foliar and stem necrosis on H. brasiliensis. These findings provide a theoretical foundation for accurate disease diagnosis, epidemiological surveillance, and the development of effective chemical control strategies for rubber plantations.