In vitro root induction in axillary microshoots of Quercus robur L.

Whilst considerable efforts have been made to optimise shoot multiplication and rooting in oak, little attention has been paid to the impact of condit ions used for multiplication on subsequent root formation. An optimised tec hnique for rooting of oak microshoots has been developed to assess the effe ct of cytokinin treatments applied to shoot multiplication cultures on the subsequent rooting of microshoots. We found IBA to be more effective at ind ucing root formation in microshoots than NAA. Efficient rooting of oak micr oshoots (80%) was achieved after 35 days on medium supplemented with 1.0 mg litre(-1) IBA. Lower concentrations of IBA reduced the frequency of root f ormation and significantly increased the time taken for microshoots to form roots. High concentrations of IBA (3.0 mg litre(-1)) produced similar root ing frequencies but with significantly increased numbers of roots formed by each microshoot. However, high concentrations of IBA stimulated the produc tion of basal callus. Rooting of microshoots was unaffected by the concentr ation of BA used during shoot multiplication, although basal callusing was greater in microshoots taken from multiplication medium supplemented with t he highest concentration of BA (1.0 mg litre(-1)) and rooted on medium supp lemented with 3.0 mg litre(-1) IBA. Reducing the period of exposure to auxi n to 7 days by transferring microshoots to auxin-free medium increased the frequency of root formation (84%), led to more rapid root formation and a r eduction in basal callus formation.