We investigated the effects of bottom-heat treatment (BHT) during low-air-temperature storage on the rooting and growth of squash cuttings after planting following storage. Rooting of cuttings was much improved with BHT temperatures ranging from 27 to 32°C, and the root fresh weight after planting increased linearly with increasing BHT duration from 0 to 24 h. Rooting during storage was observed 30 h after starting BHT, but was not observed at 26 h. BHT should end just before rooting begins to avoid the inhibition of root growth caused by root damage during planting; therefore, the optimum BHT duration is thought to be 26 to 30 h (approximately 1 day). To test the practicality of BHT in transplant production, we used cuttings obtained by grafting cucumber (Cucumis sativus L.) scions onto squash rootstock. The squash cuttings used for the rootstock were either exposed or unexposed to BHT (30°C) during storage at 9°C for 24 h, and were then grafted with the cucumber scions. One portion of the grafted cuttings was planted in growing medium immediately after grafting. Six days after planting, total and root fresh weights of the BHT cuttings were 1.3 and 4.0 times higher compared to those of the non-BHT cuttings, respectively. Another portion of the grafted cuttings was stored at an air temperature of 9°C for 7 days. The root-promoting effects of BHT were maintained during the low-temperature storage.
2007 by Japanese Society for Horticultural Science