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Eucalyptus camaldulensis x globulus hybrids for saline land: Production, seedling growth and salt / waterlogging tolerance

Oddie, Rachel Louise Annabelle (1996) Eucalyptus camaldulensis x globulus hybrids for saline land: Production, seedling growth and salt / waterlogging tolerance. PhD thesis, Murdoch University.

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The rapid development of Eucalyptus globulus Labill. plantations for the paper and pulp industry and the increasing problem of dry land salinity in the south west of Western Australia, stimulated the development of a breeding programme aimed at producing a Eucalyptus L'Herit. hybrid that combines the salt / waterlogging tolerance of selected E. camaldulensis Dehnh. clones with the high pulp quality and yield of selected E. globulus subsp. globulus families.

Controlled pollination techniques were used to produce intraspecific and interspecific hybrids. Unilateral cross incompatibility was observed between the two species. When E. globulus was used as the female parent E. camaldulensis pollen tubes failed to grow the entire length of E. globulus styles. However when E. camaldulensis was used as the female parent, interspecific crosses were successful. Five E. camaldulensis salt tolerant clones and four E. globulus families (three with known pedigree) were used to produce the crosses.

E. camaldulensis flowers were emasculated just before operculum shed. Stigma receptivity, assessed by seed production, peaked in E. camaldulensis three days after emasculation. This coincided with the style turning red and the stigma becoming enlarged, yellow and sticky. Reasonably high levels of seed (> 25 seeds per capsule and > 65 % capsule set) could also be produced when flowers were pollinated before or after day three (days 0 - 5). Pollen placed on green, dry stigmas (days 0-2) remained ungerminated until stigmas began to enlarge and become sticky. The timing of stigma receptivity varied between the E. camaldulensis genotypes.

The number of seeds produced per capsule when E. camaldulensis was selfed was 87 % less than when the clones were outcrossed. The interspecific hybrids showed a 77 % reduction in seed set compared to outcrossed E. camaldulensis. In both cases the mechanism of the partial incompatibility was not operating in the style.

Further barriers to the hybridization of E. camaldulensis and E. globulus were manifested as a high percentage of seedlings with abnormalities compared to outcrossed E. camaldulensis. The intensity of barriers to interspecific hybridization varied, with families exhibiting from 50 to 97 % abnormal progeny.

Seedlings at the two leaf stage and at six to eight months old were scored for a number of morphological characters. These were cotyledon length, cotyledon width, depth of cotyledon emargination, petiole length, lamina length, lamina width at the widest point, the vertical distance between the axillary buds at the fifth node and leaf angle (angle between the main stem and the midvein of the lamina). Overall the morphology of the hybrids (assessed by these characters) tended to be intermediate between the two parents, but more like E. globulus than E. camaldulensis.

A small number of seedlings produced from E. camaldulensis x globulus crosses were morphologically very similar to E. camaldulensis. Allozyme analysis was used to determine the parentage of these individuals. Of the six enzyme systems studied malate dehydrogenase (MDH, E.C. and 6-phosphogluconate dehydrogenase (6PGD, E.C. were the most useful in identifying E. camaldulensis x globulus hybrids. The seedlings from hybrid families with similar morphology to E. camaldulensis were identified as E. camaldulensis. All other seedlings from hybrid families were clearly of hybrid origin. The possible cause of the seed contamination in the controlled crosses is discussed.

Seven month old seedlings were screened for salt / waterlogging tolerance in a glasshouse trial. Seedlings were placed in tanks and flooded to the sand level in the pots with one fifth Hoagland nutrient solution number two for one week. The following and each subsequent week 50 mM NaCl was added to the tanks until the NaCl concentration reached 350 mM. This concentration was held for three weeks. E. camaldulensis had a greater salt / waterlogging tolerance than E. globulus based on survival and height growth rate. The performance of the hybrid families was intermediate between the two parental species. Genotypes with superior tolerance of saline waterlogging were micropropagated for further field trials.

The potential of selected E. camaldulensis x globulus genotypes is discussed in light of the preliminary results of the breeding programme.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): McComb, Jen
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