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  • Author: P. Ades x
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Summary

Severity of disease caused by Mycosphaerella cryptica (COOK) HANSF. was assessed on the adult foliage of Eucalyptus globulus LABILL. in two provenance trials (encompassing all four subspecies) and a progeny trial of E. globulus ssp. globulus LABILL. located in Victoria, Australia. Disease was relatively low in all trials (most trees with less than 15% crown severity), except for two provenances at one trial, Judbury (E. globulus ssp. globulus) and Mansfield (E. globulus ssp. bicostata), that had mean crown severities of approximately 25% and 40%, respectively. Eucalyptus globulus ssp. bicostata (MAIDEN et al.) KIRKPATR. was significantly (P < 0.01) more susceptible than E. globulus ssp. globulus, E. globulus ssp. pseudoglobulus (NAUDIN ex MAIDEN) KIRKPATR. and E. globulus ssp. maidenii (F. MUELL.) KIRKPATR., with subspecies maidenii significantly less diseased than all other subspecies. There was significant variation between provenances within subspecies globulus (P < 0.01) but not within subspecies pseudoglobulus, maidenii or bicostata. Subspecies globulus also showed significant (P < 0.01) variation between families. There was a moderate to high genetic correlation between disease of the adult foliage and disease of the juvenile foliage (caused by both M. cryptica and M. nubilosa (COOKE) HANSF.) assessed several years earlier, both at the provenance (rG = 0.67) and family (rG = 0.33) levels. Narrow sense heritability of disease of the adult foliage (M. cryptica) was low (h2 = 0.17), compared to that of the juvenile foliage (h2 = 0.35) and juvenile defoliation (h2 = 0.45) assessed previously. Selection for overall disease resistance (both adult- and juvenile-phase foliage) can be carried out more quickly and accurately at the juvenile stage when trees are 2-3 years old, potentially reducing the time required for resistant trees to be selected and deployed in the field. Mycosphaerella leaf disease on adult E. nitens (DEAN and MAIDEN) MAIDEN was also assessed in two provenance trials; however, there was very little disease observed and no significant differences were found between provenances.

Summary

Density and microfibril angle (MFA) of tension wood and normal wood were assessed in the sapwood and heartwood, from three provenanaces of 10-year-old Eucalyptus globulus Labill. Density was measured using a modified saturation method that also enabled the calculation of the extractives lost during saturation. Microdensity and MFA were determined by SilviScan 2, a rapid X-ray densitometry and X-ray diffraction system developed at CSIRO. Significant differences were found in density and extractives between provenances and also density between the sapwood and adjacent heartwood from each provenance. This result may explain some of the drying differences between provenances found in an earlier study (Washusen and Ilic 2000). Sapwood samples with high percentages of tension wood fibres had high density and a significant positive correlation was found between microdensity and tension wood fibre percentage. MFA was found to be very low in normal wood in the sapwood, where most tension wood was found, so tension wood could not be identified by MFA. The positive association between tension wood and wood density suggests that caution should be taken when selecting trees for high wood density in tree improvement programs.