Characterization and Application of Endophytic Bacteria for Enhancing Nitrogen Uptake in Vanda Orchids

Vanda orchids are a commercially significant genus in the global floriculture industry, yet their cultivation often depends on substantial chemical fertilizer inputs, which raise both economic and environmental concerns. Endophytic bacteria offer a promising, sustainable alternative by promoting plant growth and enhancing nutrient acquisition. This study aimed to characterize native endophytic bacteria and assess their potential to improve nitrogen uptake and growth in Vanda orchids. Three potent nitrogen-fixing bacterial isolates (2R13, 3S19, and 3R14) were selected for this research. Through 16S rRNA sequencing, they were identified as Curtobacteriumcitreum, Stenotrophomonas panacihumi, and Bacillus subtilis, respectively. The efficacy of these isolates was evaluated in both controlled in vitro and practical greenhouse conditions using various dilution ratios. Scanning electron microscopy confirmed the successful colonization of isolate 3S19 within the root tissue of inoculated Vanda plantlets. The results revealed a significant interaction between the bacterial treatments and the growing environment. In vitro, isolate 3S19 applied at a 1:25 ratio yielded the highest total nitrogen content (12.46 mg g−1 DW). Conversely, in the greenhouse experiment, isolates 2R13 and 3S19 were most effective at a 1:50 ratio, achieving nitrogen contents of 11.18 and 10.83 mg g−1 DW. Furthermore, bacterial inoculation in the greenhouse generally led to significant improvements in plant growth parameters, including height, leaf count, and root development, compared to non-inoculated controls. These findings highlight the potential of these endophytic bacteria as effective biofertilizers for Vanda orchid cultivation. The contrasting outcomes between the two experimental settings underscore the critical importance of optimizing application rates based on specific environmental conditions to maximize benefits in commercial production.