Calcium carbide and gibberellic acid co-application enhances drought resilience in papaya (Carica papaya L.) by modulating photosynthetic efficiency and stress markers

Background: Papaya (Carica papaya L.), a critical tropical export crop generating 14 million tons yearly, shows extreme drought vulnerability due to shallow roots, high transpiration rate, and 85% tissue water content, exceeding other tropical fruits’ sensitivity. While individual calcium carbide (CaC2) and gibberellic acid (GA3) application show promise, their synergistic potential remains unexplored. We hypothesized that the dual Ca2+/acetylene release by CaC2 interact with the growth pathways of GA3 to create novel drought tolerance mechanisms. Results: Papaya seedlings were subjected to three water levels (100%, 75%, 50% field capacity) with four biweekly treatments over 12 weeks: control (water only), CaC2 (0.31 g plant− 1 surface-broadcast), GA3 (100 mg L− 1, 50 mL plant− 1 soil-drench), and CaC2 + GA3 combination. Co-application preserved photosynthesis under severe drought (27.48 vs. 7.78 µmol CO2 m− 2 s− 1 in controls) and maintained 78% optimal biomass. Principal component analysis revealed orthogonal relationships between stress markers and performance traits where treated plants reduced proline accumulation while maintaining growth, suggesting alternative osmotic adjustment pathways. Notably, nonstomatal limitations stayed below 1000 versus 2165 in controls, indicating preserved metabolic function. Even under well-watered conditions, combined application enhanced chlorophyll a by 75% and photosynthesis by 54%, demonstrating growth promotion beyond stress mitigation. Conclusions: The hormone-mediated physiological reprogramming via CaC2 and GA3 co-application suggests alternative drought tolerance response that decouple stress perception from growth suppression. This approach provides directly deployable technology for climate-resilient tropical agriculture, with important implications extending beyond papaya plants to other high-value tropical fruits facing intensifying climate extremes.

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