The rooting of eucalyptus selections is practiced commercially on a large scale in forestry. The basic techniques are well understood. The majority of selections are from hybrids of certain sub-tropical and tropical species, though selections of temperate species such as E. globulus are also propagated by cuttings. It is very apparent from all this work that there is great variation in rooting ability between selections within species or hybrid taxa, and between different species. This is genetically determined. The speed with which cuttings initiate roots also influences rooting success; this is influenced both by genetics and by the procedures used.
Rooting of eucalyptus selections having horticultural merit is rarely practised on a commercial scale. Most eucalyptus varieties and selections that are available commercially appear to be either stable inbred lines of pure species, or are propagated by grafting; many of these have considerable horticultural merit but lack the cold-hardiness that would allow them to be planted in the UK. Thus, there is little information available on rooting of ornamental eucalyptus species, or of species having qualities that make them of interest as candidate parents in the creation of new hybrids.
Part of Prima Bio's programme therefore involves screening selections within species for their ability to root. This work started in March 2005, and uses facilities established within the East Malling Research Station.
Experiences of trying to root some eucalyptus selections in forestry nurseries indicate that traditional mist propagation is unsatisfactory for selections that do not root rapidly. The main reason is the incidence of fungal diseases in the wet conditions. Prima Bio has therefore invested in propagation facilities based on 'dry fog' - a humid environment in which there is very little deposition of water onto surfaces because the very small water droplets evaporate before they deposit. It is already clear that this type of propagation environment can work exceptionally well, but for optimal results associated procedures need to be modified also. A further benefit is that the incidence of fungal diseases is very low, even though no fungicides are used; this allows the majority of cuttings set to survive in good condition for many weeks, even if they do not root. Weaning the rooted cuttings is proving to be exceptionally easy.
The fogging system was supplied by J D Ultrasonics Ltd.