Comparisons of the morphology and physiology of cuttings and seedlings of Eucalyptus globulus

Eucalyptus globulus subspecies globulus is widely planted for pulp production. It is propagated by cuttings for tree improvement and mass deployment. Development of cuttings and related seedlings was compared to test whether vegetative propagation affects growth adversely. A clone bank was developed from seed and the two best-rooting clones from each of five families compared with seedlings from the same families under optimal, controlled water stress, and field conditions. Cuttings had similar height growth but lower diameter growth rates than seedlings under all conditions. Even under optimal conditions, the morphology of the root systems of cuttings differed from that of seedlings, and cuttings partitioned less biomass to their roots. In all comparisons clones of each family performed similarly to the mean of all cuttings, but variability was high within most clones. Shoot physiology of cuttings and seedlings was similar under optimal and water stressed conditions, but the total water use of cuttings was less than that of seedlings under sub-optimal water availability. Water relations of both plant types were preconditioned by reduced watering frequency; preconditioned cuttings died at higher residual water contents than seedlings, or cuttings watered optimally. Comparisons under field conditions were precluded by early mortality of most seedlings, but the growth and development of the cuttings was monitored for more than one year. Height growth was highly variable within clones and the uniformity expected of clonal plantations was not achieved. Root systems of cuttings and seedlings were fundamentally different. High levels of deformity were observed in the root-shoot junctions of cuttings. These deformities, which imply poor development and instability for seedlings, were not necessarily deleterious for cuttings at 13 months. Accumulated evidence suggested that the root systems of cuttings had poorer uptake and transport capacities. Anatomical examination of the root-shoot junctions showed that the vascular systems were highly distorted. The contortions probably increase resistance in the vascular pathway both by increasing its length and physical resistance. The lack of uniformity within clones was probably due to varying quality of the root systems and suggests the propagation system was inadequate. However, the presence of some individuals which grew similarly to seedlings suggests the propagation system might be modified to produce such plants. In conclusion, it is premature to plant cuttings of Eucalyptus globulus widely until the propagation system is better understood and improved. Long-term monitoring of field plantings is required to evaluate fully the effect of root system morphology and to define the optimal root system for cuttings