Induction of drought resistance by abscisic acid and paclobutrazol in jack pine

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Pretreatment with root drenches of abscisic acid or paclobutrazol increased the resistance of jack pine (Pinus banksiana Lamb.) seedlings to subsequent prolonged drought. During drought, seedlings pretreated with abscisic acid or paclobutrazol exhibited rapid stomatal response, more favorable water potentials, enhanced water retention and increased survival compared with control seedlings. Maximum differences in survival between pretreated and control seedlings were observed late in the drought period with survival values of 100, 89, and 0% in the abscisic acid, paclobutrazol, and control treatments, respectively. Paclobutrazol was also effective in protecting seedlings from a combination of intense heat (≥ 40 °C), low humidity, and drought, with survival values of 89 and 0% for the paclobutrazol-treated and control seedlings, respectively.