Plant-growth-promoting rhizobacteria (PGPR) influence soil fertility, plant growth, tolerance to abiotic stress, resistance to herbivorous insects, and plant interactions with other organisms. While the effects of PGPR on plant growth, fruit yield, and induced defense responses have been extensively studied, the consistent positive outcomes have fueled rapid expansion in this research field. To evaluate PGPR impacts on plant growth and interactions with phytophagous insects, we conducted a systematic meta-analysis using publications from electronic databases (e.g., PubMed, Web of Science) that reported PGPR effects on plants and insects. Effects were categorized by plant family, PGPR genus, insect feeding guild, and insect–host specialization. Our analysis revealed that PGPR generally enhanced plant growth across most plant families; however, the magnitude and direction of these effects varied significantly among PGPR genera, indicating genus-specific interactions with host plants. When assessing PGPR-mediated reductions in phytophagous insects, we found that Pseudomonas, Rhizobium, and Bacillus exhibited the weakest negative effects on insect populations. PGPR significantly reduced both monophagous and polyphagous insects, with the most pronounced negative impacts on sucking insects (e.g., aphids, whiteflies). This study highlights critical patterns in PGPR-mediated plant growth promotion across taxa and the related differential effects on phytophagous insect activity. These insights advance our understanding of PGPR applications in agroecological production systems, particularly for integrated pest management and sustainable crop productivity.

In vitro cultivation of arbuscular mycorrhizal fungi (AMF) is challenging due to their biotrophic symbiosis. The principal aim of this study was to demonstrate the effect of establishing in vitro dual cultures of arbuscular mycorrhizal fungi (AMF) inoculated on Swietenia macrophylla (mahogany) roots on plant growth. Furthermore, it was sought to demonstrate that plant colonization by Glomeromycota can be achieved with a replicable protocol. This study established monoxenic cultures of carrot (Daucus carota) Ri T-DNA ROC inoculated with Glomus sp. on two-compartment plates. At 75 days, hyphal growth reached 223.93 mm in the root compartment and 103.71 mm in the hyphal compartment. Spores produced in vitro measured 26.14 ± 1.70 µm, smaller than ex vitro spores (101.2 ± 4.22 µm). Rhodotorula mucilaginosa was isolated from cultures and appeared to stimulate hyphal growth and root–fungal contact. From these cultures, a dual culture of mahogany inoculated with Glomus sp. was established. No significant differences were observed between inoculated and non-inoculated plants in stem length, root length, root number, or leaf number at 30 days. Spore production ranged from 10,166 to 27,696 per plate, averaging 14,795 ± 3301, with hyphal lengths of 3655.46 ± 308.75 mm. Hyphal development included running and branching patterns, with solitary and clustered spores. Spore diameter averaged 27.68 ± 3.85 µm. Arbuscular colonization reached 41.49% at 30 days and 52.13% at 75 days, exceeding rates reported for other culture systems. Monoxenic cultures are a reliable, aseptic source of high-quality inoculum, supporting biofertilizer production and biotechnological applications. These methods provide valuable tools for studies involving AMF, such as those demonstrated with mahogany.

The nitrogen-fixing symbiosis with rhizobia significantly contributes to the successful establishment of legumes in tropical environments. Here, we explored the symbiotic interactions between legumes and rhizobia across 109 tropical species. We evaluated the presence of root nodules in 72 genera spanning four Fabaceae subfamilies, encompassing 53% of the genera in Costa Rica and approximately 9.4% globally. Our analysis revealed root nodules in 78% of the species belonging to Caesalpinioideae (67%) and Papilionoideae (84%). Also, we formulated a predictive model for nodulation in legumes, with fine-root color and flower symmetry as the main predictor criteria. Nodulating taxa consistently presented higher N levels in tissues, thinner roots, and a pronounced phylogenetic influence on nodulation. We also identified the bacterial genera associated with all nodulating legumes. Caesalpinioideae formed symbiotic relationships with ten rhizobial genera, whereas Papilionoideae were associated with only four. Bradyrhizobium emerged as the predominant symbiont in nodules, while Rhizobium, Mesorhizobium, Agrobacterium, Paraburkholderia, and Cupriavidus exhibited a more restricted host range. Furthermore, genomic analysis suggests that 15 out of the 22 sequenced rhizobial strains may represent novel species. Our study enhances the understanding of the different dimensions that comprise legume-rhizobia interactions, incorporating a diverse array of previously unexamined tropical forest legume taxa.