Application. Micropropagationof Eucalyptus may be an important tool for tree improvement and reforestation programs. Plantlets may be used for establishment of clonal seed orchards, testing of clonal candidates, and operational planting. Also, large numbers of clonal plantlets may be micropropagated for physiological and silvicultural studies when genetic uniformity is desired.Abstract. Three superior clones of Eucalyptus grandis hybrids were micropropagated through several steps. Five-year-old trees were girdled to induce juvenile sprouts. Cultures were attempted from mature branches and sprouts. Branches from mature trees were 100% contaminated while sprouts were only 40% contaminated. Pre-initiation hormone free medium and dark environment were used to screen for contaminants and to reduce production of phenolic compounds. Initiation of auxillary buds was achieved with modified MS plus 0.05 mg/l NAA and 0.5 mg/l BAP. High multiplication rates were obtained on auxin-free medium with 0.6 mg/l BAP. Elongation of shoots was best on media with high auxin (2.5 mg/l of IBA) and cytokinin (l-l.5 mg/l of zeatin). Continual subculture on the multiplication medium improved rooting significantly. Up to 98% rooting was achieved on l/4 MS with 2 mg/l IBA. Rooted propagules were successfully transferred to a mist greenhouse with 82% survival, and then to greenhouse conditions.

Callus of three superior Eucalyptus grandis hybrids was induced from immature inflorescences, floral parts, shoot tips, zygotic embryos, and hypocotyl explants on various auxin (2,4-D or NAA) and cytokinin (kinetin) supplemented media. Hypocotyl callus initiated on 4 mg/l NAA and 1 mg/l kinetin formed massive nodular structures, and shoots and roots after four weeks on hormone free-medium. Callus from all other expiants turned brown and died upon transfer to hormone free or reduced hormone media. The nodular structures originating from hypocotyl-callus were maintained by subculture for over three years and retained the ability to form thousands of shoots. Shoots were successfully rooted (98% rooting) and plantlets developed were transferred to mist-greenhouse and then to greenhouse conditions with 95% survival. Plantlets were grown for six months in the greenhouse without sign of abnormal growth.

Application. Understanding the relationship between ethylene and chlorophyll concentration during water stress could provide a means for developing a method to determine drought susceptibility in Eucalyptus and perhaps other important species . Drought tolerance appeared to be associated with higher chlorophyll concentration and lower ethylene production rate .Abstract. A study was conducted with seven-month-old plantlets, of the clone 2814 of Eucalyptus grandis x E . camaldulensis Dehnh . hybrid and of the clone 2798 of E. grandis x E. robusta Sm ., subjected to sublethal water stress . During the imposed drought, leaf water potentials and transpiration rates decreased, while ethylene production and leaf chlorophyll concentration increased to a maximum during the onset of water stress, and then declined . Stomatal closure coincided with or preceded maximum ethylene production . A saturation type relationship between ethylene production and chlorophyll concentration was observed . Genotypic differences in the response to water stress occurred between clones with clone 2814 appearing to be a drought avoider and clone 2798 a drought tolerator.

Tissue culture-derived plantlets from three superior five-year-old Eucalyptus grandis Hill ex Maid hybrids were compared to their related half-sib seedlings under greenhouse conditions. Net photosynthesis, chlorophyll a and b concentrations, and nitrogen concentration were sampled four times at 40-day intervals. Comparisons were started 40 days after plantlets and germinating seedlings were moved from mist to greenhouse conditions. Seedlings had higher net photosynthesis, chlorophyll and nitrogen concentration at early harvests. However, as the study progressed the difference between plantlets and seedlings decreased and reached similar values. No family differences were observed regardless of plant origin (seedlings or plantlets). Plantlets and seedlings showed similar general trends in all the measured parameters over the four harvests.

In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time.