Distinct effects of auxin and light on adventitious root development in Eucalyptus saligna and Eucalyptus globulus

Adventitious rooting is essential for vegetative propagation of woody speci es. We studied the effects of auxin and light on the development of adventi tious roots in cuttings obtained from seedlings of Eucalyptus saligna Smith and E. globulus Labill in an attempt to characterize the adventitious root ing process and identify factors controlling rhizogenesis. Root development was scored as rooting percentage, root density (roots per rooted cutting), mean rooting time and root length, In both species, rooting time was reduc ed in the presence of auxin, Cuttings from 2-month-old E. saligna seedlings were responsive to lower auxin concentrations than comparable cuttings fro m E. globulus seedlings. Cuttings from 3-month-old E. saligna seedlings roo ted promptly and rooting was not significantly affected by light conditions . In contrast, rooting of cuttings from 3-month-old E, globulus seedlings e xhibited recalcitrant behavior and no roots were formed if illuminated duri ng the root formation phase. Effective root regeneration of E. globulus cut tings was obtained by a 4-day exposure to 10 mg l(-1) IBA and culture in da rkness during the root formation step. Loss of rooting capacity with seedli ng age was more pronounced in E, globulus than in E. saligna. The possibili ty of switching adventitious rooting off and on by manipulating light regim e and exogenous auxin supply in E, globulus, and the constitutive nature of rooting in E, saligna may provide useful models for examining the rooting process at the biochemical and molecular levels in Eucalyptus.