Chitosan and Stenotrophomonas Foliar Spray Synergistically Promote Productivity, Phytochemical Status, and Mineral Composition in Papaya Under Tropical Conditions

Sustainable and quality papaya production faces challenges, especially under the unstable tropical summer agroecosystems. However, biostimulants offer a promising approach to improve crop performance, even under unfavorable conditions. Therefore, the study explored the effects of chitosan and Stenotrophomonas maltophilia on papaya productivity and fruit quality under tropical conditions. Besides enhancing plant growth, chitosan at 750 (C 3 ) and 1000 (C 4 ) ppm combined with S. maltophilia at 7.0 × 10 8 CFU mL −1 (P 3 ) significantly improved fruit production and quality over untreated plants. Notably, the chitosan– Stenotrophomonas consortium (C 4 P 3 ) maximized the fruit yield (19.57 kg plant −1 ), representing a 114.1% increase compared with control (9.14 kg plant −1 ). Higher‐concentration treatments (C 4 P 3 and C 3 P 3 ) also significantly enhanced fruit size, total soluble solids, sugars, β‐carotene, ascorbic acid, phenolics, and flavonoids by 40.1%, 55.9%, 91.5%, 300%, 114.6%, 106.3%, and 73.3%, respectively, over control. Besides, C 3 P 3 improved mineral accumulation by 60.0%–122.3% compared with control. Conversely, treatments containing chitosan or bacteria alone were statistically inferior to the combined treatments, like the control. Furthermore, heatmap clustering distinctly positioned the higher‐dose combined treatments with superior yield, quality, antioxidant, and mineral traits against the control and low‐dose single treatments, highlighting a clear chitosan–bacterial synergy for improving papaya under the tropical environments.