Autecology of Cassia brewsteri with respect to galactomannan production

Cassia brewsteri (Caesalpiniaceae) is a tree endemic to central Queensland. In this thesis, the potential of the plant as a source of seed gums (galactomannans) with industrial applications has been assessed in terms of genetic diversity, distribution and habitat, phenology, propagation, insect pests, seed chemistry, gelling characteristics and economic viability. Radio-labelled DNA Amplification Fingerprinting was used to indicate the level of genetic variation within C. brewsteri. Phylogenetic analyses supported the maintenance of the four native Cassia taxa at species level and the division of C. brewsteri into two subspecies. Ecological parameters associated with 124 sites of natural or cultivated occurrence were characterised in terms of soil and vegetation type, and potential cultivation areas predicted using the climate modelling software BIOCLIM. A broad area of eastern Queensland was shown to be suitable for the cultivation of the tree. Reproductive phenology of the tree was documented and found to allow for a confined harvest period (once per year). Seed germination was achieved most effectively by mechanical scarification while propagation by rooted cuttings was unsuccessful. Heavy predation of seed by Caryedon serratus (an exotic bruchid) was noted, and the potential impact of this insect on the ecology of its host, and the potential for infestation of Arachis hypogaea (peanut) is discussed. Cassia brewsteri seed galactomannan was demonstrated to be acceptable for use as a food gum. It is comparable to Ceratonia siliqua ( carob) gum in gelling strength, and contains less than 10 ppm of the toxin chrysophanic acid. However, preliminary estimates of yield and return on investment from plantation culture of Cassia brewsteri for seed production were not encouraging.