Reducing fruit cracking and increasing TSS in greenhouse muskmelon by decreasing net fruit water accumulation under mild deficit irrigation during the reproductive stage

Fruit water accumulation through the vascular system is essential for fruit growth, yield, and quality formation, but it is also a major driver of fruit cracking. However, the mechanism by which net fruit water accumulation affects muskmelon cracking under different irrigation regimes remains incompletely understood. Therefore, we conducted an experiment with three irrigation levels during the reproductive growth stage of muskmelons: full irrigation (W0, 100% ET), mild water deficit irrigation (W1, 75% ET of W0), and severe water deficit irrigation (W2, 50% ET of W0). In this study, we investigated how irrigation regulates fruit cracking and quality by influencing net fruit water accumulation, focusing on the interrelationships among muskmelon fruit pedicel structure, stem-fruit water potential gradients, pedicel hydraulic conductance, cracking rate, and quality. Deficit irrigation reduced fruit cracking by 52.94–76.47%, and increased TSS by 14.77–21.88%. Net fruit water accumulation was more sensitive to pre-dawn and midday stem-fruit water potential gradients and pedicel hydraulic conductance during the flowering-expanding stage than during the fruit maturity stage. Although plants partially compensated for the negative effects of water deficit on pedicel hydraulic conductance by increasing vessel number and density, reductions in xylem vessel diameter and area still decreased pedicel hydraulic conductance. Random forest analysis further indicated that vessel diameter and vessel area were the most important structural indicators affecting xylem hydraulic conductance. Overall, these results suggest that deficit irrigation reduced stem-fruit water potential gradients and pedicel hydraulic conductance by decreasing vessel diameter and area, thereby regulating fruit net water accumulation and reducing fruit cracking. This study provides new insight into reducing muskmelon fruit cracking by regulating fruit water accumulation through deficit irrigation.