We investigated the effects of supplying warmed water to the graft union of tomato and eggplant grafted cuttings during low-air-temperature storage on graft development and plant growth after storage. The scions of grafted cuttings were held at an air temperature of 9 to 12°C, while the region from the cut end of the rootstock cuttings to the graft union was held at 12 to 37°C in water during 4 days' storage. The tensile strength of some cuttings' graft union was measured as an index of graft development. The tensile strength of the tomato graft union was much improved when the graft union temperature ranged from 23 to 27°C. That of the eggplant graft union increased as the temperature rose up to 29°C. After 4 days' storage, the remaining cuttings were planted in vermiculite medium and grown in a growth chamber. Cuttings from the temperatures that gave a higher tensile strength tended to grow larger. We also investigated the effects of supplying the water at 28°C to the graft union on the storage quality of cuttings by measuring the water status, gas exchange, and chlorophyll fluorescence parameters after 4 days' storage at an air temperature of 9 to 11°C. The leaf water potential and leaf conductance of scions with warmed graft unions were significantly higher than those with unwarmed graft unions. The chlorophyll fluorescence parameters Φ PSII and the electron transfer rate were maintained with warmed water during storage, but were significantly decreased without warmed water application. These results indicate that keeping the graft union warm during low-air-temperature storage can improve graft development, storage quality, and plant growth after storage.

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