Configuration and development of root systems of cuttings and seedlings of Eucalyptus globulus

Stem cuttings of Eucalyptus globulus are used within tree improvement programs and for mass deployment. To be successful, cuttings must perform as well or better than seedlings. The root systems of cuttings are fundamentally different from those of seedlings. If these differences influence growth, the differences and their consequences must be identified and the propagation system manipulated to improve performance of the propagules.Cuttings are only a viable alternative to seedlings as planting stock if the method of propagation does not affect their growth and development adversely. Full-sibling cuttings and seedlings of Eucalyptus globulus were compared under controlled environmental conditions to minimise extraneous sources of variation, and to establish whether changes in growth or development were induced by propagation. On three occasions over a period of eight weeks root-collar diameter, shoot height, leaf and stem weight, shoot/root ratios and root system morphology were measured on cuttings and seedlings. Seedlings were taller than cuttings throughout the experiment, but both plant types had similar height growth rates. Diameter growth rates were lower in cuttings than seedlings, and there were differences in both height and diameter growth rates between families. Root system configuration differed between the plant types. Seedlings had strongly gravitropic tap-roots, with two types of primary roots from which secondary roots emerged. Cuttings had no tap roots, and the main structural components of their root systems were adventitious roots formed during propagation. Cuttings did not develop further structural roots during the experiment, whereas seedlings continued to develop primary roots. Individual primary roots of cuttings were longer and had larger mid-point diameters than those of seedlings, but the total length of primary roots was greater in seedlings. Seedlings also had a greater number and total length of secondary roots. Shoot/root ratios, calculated from a range of functional measures, were higher in cuttings than seedlings.