Adventitious root formation in Backhousia citriodora F. Muell : the stock plant barriers

Kibbler, Harry. (2002). Adventitious root formation in Backhousia citriodora F. Muell : the stock plant barriers PhD Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

       
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Author Kibbler, Harry.
Thesis Title Adventitious root formation in Backhousia citriodora F. Muell : the stock plant barriers
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2002
Thesis type PhD Thesis
Supervisor Margaret Johnston
Richard Williams
Total pages 200
Language eng
Subjects 0706 Horticultural Production
Formatted abstract The vegetative propagation of Backhomia citriodora from cuttings was studied to identify barriers to the formation of adventitious roots.

B. citriodora is a member of the family Myrtaceae and typical of many woody Australian species that have similar problems in forming adventitious roots from cuttings. The identification of barriers that prevent the formation of adventitious roots in B. citriodora has implications for other woody Australian species.

An investigation of the propagation enviroimient to maximise rooting showed no significant differences between the 3 environments tested. Therefore the propagation environment is not the main barrier to adventitious root formation. The 8 to 24 weeks required to form roots means characteristics of cuttings that increase survival are an advantage. The survival of cuttings was increased when they were selected with the characteristics of wide stems, reduced mature leaves and a node within 20 mm of the base. In contrast, the removal of axillary buds promoted early rooting in both autumn and winter.

A two-year study was carried out on established trees at two sites in south eastern Queensland, Australia to identify environmental factors that influenced rooting. Complex interactions of rainfall events above 20 mm from the preceding month and mean maximum temperature on stock plants resulted in a correlation with rooting success of r=0.81 and r=0.74 for sites at the University Of Queensland Gatton campus and Cedar Glen respectively. A more detailed investigation under controlled environmental conditions showed that maintaining stock plants at temperatures between 10 °C and 30 °C had no direct effect on rooting capacity. However, temperature was correlated with growth, which may have an indirect effect on root formation. In spring floral initiation was found to only delay rooting and had no effect on the final rooting percentage.

B. citriodora genotypes were identified that differ in their ability to form adventitious roots from cuttings. Also, differences in the rooting ability conferred by juvenile and mature stock plants were confirmed. The comparison of identified stock plants were used as a basis to investigate the physiological barriers to adventitious root formation.

A series of seasonal experiments demonstrated that application of the auxins indole-3- acetic acid, indole-3-butyric acid and napthaleneacetic acid over a range of concentrations (1000 - 8000 µg/ml) did not significantly increase rooting compared to the control.

The final series of experiments identified an inverse correlation between the level of citral and the rooting capacities of juvenile, easy- and difficult-to-root genotypes. The results satisfy Hackett's criteria for the involvement of citral as an endogenous inhibitor of root formation in B. citriodora i.e. The substance extracted from B. citriodora was identified as citral, a mixture of neral and geranial. A correlation was established between endogenous levels of citral and the rooting capacities of juvenile, easy- and difficult-to-root genotypes. When citral was applied to B. citriodora seedlings in concentrations similar to the endogenous levels they came between a range of concentrations that inhibited rooting at the higher level and had no effect at the lower level. Citral is an endogenous inhibitor of root formation in B. citriodora that explains some of the decrease in rooting after maturation and in some genotypes.

The main conclusion was that the presence of citral in the shoots from which cuttings are taken is the primary barrier to adventitious rooting of B. citriodora cuttings. Other conclusions and practical recommendations for cutting propagation of B. citriodora are included with the conclusions.
Keyword Budding (Plant propagation)
Plant cuttings -- Rooting

 
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