From in vitro cultured adult material of Corylus avellana L. cv. Negretta, adventitious rooting of microshoots was evaluated. Rhizogenic induction mediated by two strains of wild-type Agrobacterium rhizogenes (A477 and A478) and indolbutyric acid (IBA) were compared under two light conditions (16:8 h photoperiod and complete darkness). The results indicate that in the 16:8 h photoperiod induction, the rooting rate with IBA (90%) was significantly higher than that obtained with the strain A477 of A. rhizogenes (67.7%), while with the strain A478 no statistically significant difference was obtained for the same variable (75%). On the other hand, under complete darkness, rooting mediated by IBA (90%) significantly surpassed the results obtained with both strains of A. rhizogenes (40 and 20%, for A478 and A477, respectively). In terms of the morphological variables of the resulting root system, induction mediated by IBA, with a 16:8 h photoperiod, generates a significantly higher number of roots (19 roots per microshoot) than that obtained with A. rhizogenes (mean 3.7 roots per microshoot), producing significant differences when comparing the results with the strain A478 (5 roots per microshoot) to those of the strain A477 (2.4 roots per microshoot). Induction under complete darkness does not have any effect on root number, independent of the rhizogenic inductor employed. Root length did not present significant differences among treatments, except in the presence of A. rhizogenes A477 and darkness.