No abstract

A series of experiments on field-grown seed-derived trees between 2 and 17 years old demonstrated that the growth regulator paclobutrazol could be used to reduce vegetative growth and enhance flower-bud production in Eucalyptusglobulus Labill. and Eucalyptusnitens (Dean & Maid.) ex Maid. Responses to high levels of trunk injection and collar drenching persisted for up to six growing seasons, yielding both increases in frequency of flowering and heaviness of bud crop. Growth responses were expressed in the immediate growing season, but flowering responses were not evident for another year. Foliar spray treatments reduced vegetative growth in young trees of both species for one growing season, but only the E. globulus showed an associated flowering response. Assessment of seed yield per capsule and subsequent germination tests showed no deleterious effects on seed development or quality. Choice of application method will vary with objective and size of tree. Collar drenching shows the most promise for treating large numbers of seed orchard trees because application time is substantially independent of tree size and weather conditions.

No abstract

Adventitious buds and shoots of Eucalyptus globulus Labill. (Tasmanian Bluegum) have been regenerated from cotyledons and hypocotyls from mature embryos and seedlings. Adventitious buds were induced at high frequency with 0.05 mM thidiazuron in combination with 0.2 mM 2,4-dichlorophenoxyacetic acid or 5 mM a-naphthaleneacetic acid. Culture of explants in the dark inhibited bud induction, but up to 86% of cotyledons, longitudinally split just prior to culture, produced adventitious buds in the light. Development of buds into shoots occurred only at low frequency, after transfer to media containing N 6 -benzylaminopurine.

Node-derived shoot cultures of Eucalyptus regnans were established from in vitro grown seedlings on Murashige and Skoog basal medium supplemented with 0.5 mg L-' (2 pm) zeatin and 0.05 mg L-I (0.3 pm) napthaleneacetic acid. A double sterilisation method was essential to obtain clean material from seed. Microcuttings from established cultures were used to develop an efficient method for in vitro rooting. Rooting was best after a 7 day pulse on 20 mg L-I (98 pm) indolebutyric acid. Hoagland's or Woody Plant Medium supported better rooting than MS basal medium and rooting was significantly enhanced by subculture to activated charcoal after the auxin pulse. Carbohydrate (sucrose or glucose) was essential for rooting while high light intensity was inhibitory. Optimal light conditions were a 12 h day (17 W m-2). In all, 90% of plantlets established in the nursery survived the winter.