Root-Zone Temperature Influences Overwinter Survival and Post-Winter Recovery of Papaya

Cold injury is a major limiting factor for tropical fruit cultivation in temperate regions. Papayas are particularly sensitive to low temperatures, and exposure to 12–14 °C significantly inhibits their growth. This study determined whether combining root-zone heating with minimal greenhouse heating could improve overwinter survival and recovery under low-temperature stress conditions. Root-zone temperature was maintained above 15 °C throughout the overwintering period. Conversely, the greenhouse temperature was set at the minimum level required to avoid exposure to freezing temperatures. Tree responses were measured based on survival rate, shoot growth, SPAD, and stomatal conductance in three treatments: root-zone heating with minimal greenhouse heating, conventional whole-greenhouse heating, and a minimum-heating control. Root-zone heating with minimal greenhouse heating enabled successful overwinter survival and recovery. It exhibited comparable plant performance to conventional whole-greenhouse heating, whereas all plants in the control treatment died. Stomatal conductance recovered more rapidly in trees receiving root-zone heating than in those receiving conventional whole-greenhouse heating, suggesting earlier resumption of physiological activity. These results demonstrate that root-zone temperature management can mitigate low-temperature stress and promote post-winter physiological recovery, thus providing a potential strategy for overwintering tropical crops with reduced reliance on greenhouse heating.