In the olive Olea europaea (L.), the polyamides (PAs), putrescine, spermidine, and spermine, when added exogenously at a concentration of 1 mm in the in vitro rooting medium, combined with 5 μm auxin concentration, promoted early rooting and increased the final rooting percentage and the number of roots per explant. The effect was less evident in olive explants rooted with the basal blanching method; thin-layer chromatography of total endogenous PAs in `these explants revealed lower levels on day 2 compared with controls, while by day 5 PA concentrations in both had fallen to similar levels. Furthermore, putrescine decreased the pH of the medium by 0.5 units around the explants. PAs had little effect on apple Malus pumila (Mill.) and no effect on almond Prunus dulcis (Miller) D.A. Webb and pistachio Pistacia vera (L.). There were also some positive effects observed, but only in olive, when rooting was induced by Agrobacterium rhizogenes in auxin-free medium. Few plantlets showed agropine-positive roots.
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