Improving the Early Growth of Woody Cuttings by Warming the Basal End At Low Air Temperature

We investigated the effects of warming the basal end of poplar cuttings at low air temperature on their early growth after planting, to develop an advanced propagation technology that can provide the cuttings in which rooting preparation are well advanced regardless of the weather. [Expt. 1] Single-node leafy cuttings of poplar (Populus × canadensis) were warmed with a temperature of 30ºC or non-warmed, at an air temperature of 10ºC and a photosynthetic photon flux density (PPFD) of 10 µmol·m^-2·s^-1 with continuous lighting in a cold chamber for 8 days. The warming treatment was applied to the cuttings by soaking the basal end of cuttings in warmed water. The cuttings were supported by insertion up to the cut-end in a hole in an adiabatic board floating on the water. The warmed and non-warmed cuttings were then grown in a growth chamber at air temperature of 30ºC and a PPFD of 100 µmol·m^-2·s^-1 for 8 days. Control cuttings were grown at air temperature of 30ºC and a PPFD of 100 µmol·m^-2·s^-1 for 16 days immediately after obtaining the cuttings. The shoot dry weights of warmed and non-warmed cuttings after the growing period were greater than that of control. The leaf necrosis of cuttings was reduced in warmed cuttings compared with non-warmed and control cuttings. There was no significant difference between root growths of warmed and control cuttings. The warming treatment at a low air temperature probably reduced water stress of the cuttings by improving their rooting after the start of growing. [Expt. 2] The warming treatment (30ºC) was applied to poplar cuttings with dormant terminal bud for 18 days at the beginning of 46 days’ low temperature (5ºC) storage. Non-warmed cuttings were stored 46 days without the treatment. The warmed and non-warmed cuttings were then grown in the growth chamber at air temperature of 25ºC and a PPFD of 100 µmol·m^-2·s^-1 for 63 days. The control cuttings were grown in the growth chamber for 109 days immediately after obtaining the cuttings. The both rooting and sprouting was improved in warmed cuttings, whereas the only rooting or spouting was improved in control or non-warmed cuttings, respectively.