Bacillus haynesii VWC18 Drives Growth and Flowering Improvements in Euphorbia pulcherrima and Cyclamen persicum: A Sustainable Approach for Ornamental Crop Performance

This study evaluated the microbial strain Bacillus VWC18, isolated from waste vegetable compost, as a plant growth-promoting rhizobacterium (PGPR) for two high-value ornamental crops: poinsettia (Euphorbia pulcherrima) and cyclamen (Cyclamen persicum). Identified as Bacillus haynesii, the strain VWC18 showed robust phosphate, potassium, and zinc solubilization, siderophore production, and indole-3-acetic acid synthesis, with γ-hemolytic biosafety confirmation. Greenhouse trials evaluated its biostimulant activity by comparing control plants (three cultivars of each species) under standard commercial protocols with those receiving B. haynesii VWC18 via sub-irrigation. Treated poinsettias exhibited 90% greater fresh foliar weight in white cultivars and over 50% increased root biomass, while red varieties produced twice as many pigmented bracts. Cyclamen nearly doubled fresh leaf and root weight. Photosynthetic pigments (chlorophyll-a, chlorophyll-b, and carotenoids) approximately doubled in both species. Anthocyanin content increased significantly in red and orange poinsettia bracts and red/violet cyclamen flowers. Quantitative PCR, targeting soil eubacteria, confirmed an increase of rhizosphere communities, with bacterial populations rising from ~5 × 105 to 1–2.6 × 107 CFU g−1 soil. B. haynesii VWC18 enhances vegetative growth and aesthetic quality through phytohormone production, nutrient mobilization and rhizosphere modulation, offering a strategy for sustainable input solutions in greenhouse floriculture while maintaining marketable quality.