Effect of fusicoccin on adventitious root formation of birch shoot tips (Betula pendula Roth) cultured in vitro

The effect of fusicoccin (FC) on adventitious root formation was investigated using in vitro shoot tip cultures of birch (Betula pendula ROTH) as test system. Treatment with 10−7–10−5 M FC hastened root appearance as well as 5 × 10−6 M IAA did. Optimal FC concentrations also promoted rooting by increasing the root number per cutting. FC application during the first 48 hours of culture was enough to obtain these effects. Using internode segments without any bud it was shown that FC could not replace the root inducing activity of endogenous auxin as applied IAA did, but FC lowered the threshold concentration of IAA for rooting response and stimulated adventitious root formation if it was applied with IAA simultanously. Root growth was enhanced in the early phase but inhibited later by continuous treatment with FC. Some aspects of possible FC IAA interactions are discussed.