I.J. Bennett

Alternating Cytokinins in Multiplication Media Stimulates in Vitro Shoot Growth and Rooting of Eucalyptus globulus Labill

Shoots of Eucalyptus globulus Labill. cultured on shoot multiplication media containing, on alternate subcultures, 6-benzylaminopurine (BAP) or 6-furfurylaminopurine (kinetin), showed better growth than cultures in which either of the cytokinins was used continuously, or both were used in an equimolar mixture. When BAP was used continuously in the medium (i.e. in every subculture), shoots multiplied but remained stunted and leaves became red and abscised. Kinetin or 6-dimethylallyaminopurine (2iP) used continuously in the medium induced very low multiplication but the shoots did not become red nor did the leaves abscise. Shoots taken from multiplication medium containing BAP and placed on rooting medium with 10 microM indole butyric acid (IBA) produced few roots and often died while on the rooting medium. In contrast, shoots from the multiplication medium containing kinetin produced more roots and remained healthy during the passage on the rooting medium.

The Influence of Ammonium Nitrate, pH and Indole Butyric Acid on Root Induction and Survival in Soil of Micropropagated Eucalyptus globulus

Rooting of Eucalyptus globulus shoots was influenced by the concentration of the indole butyric acid (IBA) and NH4+ in the root-induction medium. Optimum plantlet vigor and survival were achieved using low concentrations (1 – 2.5 μM) of IBA and when NH4NO3 was removed. Removal of NH4+ also had a significant effect on medium pH, its presence caused a decrease in pH as the culture period proceeded. When different nitrate compounds (excluding NH4NO3) were used as the nitrogen source, the medium pH was more stable and this was associated with higher root production. The higher root production, in association with appropriate IBA concentrations, produced plantlets with higher survival and better growth on transfer to soil.

Comparisons of selected and cloned plantlets against seedlings for rehabilitation of saline and waterlogged discharge zones in Australian agricultural catchments

Summary Clonal lines of Australian tree species have been developed for tolerance to saline and/or waterlogged conditions. These clonal plants have been shown to be more tolerant under glasshouse and field conditions when compared with seedling lines. Selection procedures included the initial collection of seed from trees growing naturally in seasonally waterlogged and/or saline soils. Following germination and establishment, three-month-old seedlings were stressed in glasshouse trials using progressively increased levels of salinity, either in freely drained or saturated conditions, and the most tolerant individuals were micropropagated. Under conditions of saturation and salinity stress, in both glasshouse trial conditions and under field situations, selected and cloned Eucalyptus cawaldulensis. E. spathulata subspecies spathulata, Casuarina obesa and C. glauca plants showed higher survival rates and the surviving plants grew faster than provenance-matched seedlings.

Comparisons of growth of Eucalyptus camaldulensis from seeds and tissue culture: root, shoot and leaf morphology of 9-month-old plants grown in deep sand and sand over clay

Comparisons of early growth of tissue culture clones and seedlings of Eucalyptus camaldulensis indicated strong morphological differences between genotypes within the species, but no architectural differences, either above-or below-ground, were attributable to micropropagation. Clonal 9-month-old plants were less variable than seedling populations. Both seed-origin plants and clonal-origin plants generally developed a number of deep sinker roots and showed equal ability to penetrate heavy clay soils. One clonal line, however, had a compact habit and a root architecture concentrated in the upper 20 cm of the soil profile. Under favourable nutrient and water conditions, the largest of the 9-month-old plants from both seed and tissue culture exceeded 2.5 m in height, produced more than 500 g of above-ground biomass and developed root lengths exceeding 8 km. Clonal Eucalyptus camaldulensis have advantages in plantation conditions with saturated, saline and heavy soil conditions.

A comparison of growth of seedling and micropropagated Eucalyptus marginata (Jarrah) I. Early growth to 2 years

Growth and morphology of Eucalyptus marginata seedlings was compared, in glass-house and field experiments, with micropropagated plantlets derived from the crowns of mature trees. In the glasshouse experiment, the plantlets were shorter and more branched than seedlings; leaf shape and arrangement resembled mature, not juvenile, foliage. The total root length of plantlets was less than seedlings, but diameters were similar. The two soil types used in the glasshouse experiment, a peat/sand mixture and lateritic forest soil, affected the growth of the plants, probably due to the different cation exchange and waterholding capacities of the soils. In the field, after two years growth in lateritic soil, micropropagated plants were taller than seedlings, had no lignotuber and lacked the basal coppice growth which is typical of E. marginata. There is considerable difference between seedlings and micropropagated plants in form, growth and survival.

Inoculation of Eucalyptus marginata Donn ex Sm. (jarrah) clones with Phytophthora cinnamomi Rands in vitro and under glasshouse conditions

Jarrah trees surviving on jarrah dieback sites or seedlings surviving inoculation with Phytophthora cinnamomi under glasshouse conditions were propagated using tissue culture techniques. Clones and seedlings of jarrah were inoculated with zoospores in vitro and under glasshouse conditions. When inoculated in vitro individual clones showed a consistent response, between trials, with regard to time to infection. After inoculation in the glasshouse all seedlings became infected and had reduced growth, but the level of infection of the root system and the reduction in the growth of the plants varied between clones.

Testing the expression of resistance to insect attack: Resistance of jarrah (Eucalyptus marginata) to jarrah leafminer (Perthida glyphopa)

Micropropagated ramets of jarrah considered to be relatively resistant to jarrah leafminer were grown in the field and became infested with the moths larvae. Mean mine size, which was used as a measure of resistance, differed between years, as did the number of completed mines. However, within each year, ramets developed mines of the same mean size as each other the ortet. Their resistance relative to other trees was consistent over a 5-year period.