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Rural Industries Research & Development Corporation
Summary of full report
July 2001
RIRDC Project No. UCQ-12A
Executive Summary
Cassia brewsteri (Caesalpiniaceae) is a tree endemic to central Queensland. In this project, the potential of the plant as a source of seed gums (galactomannans) with industrial applications has been assessed in terms of genetic diversity, ecological requirements, phenology, propagation, insect pests, seed chemistry, gelling characteristics and economic viability. Randomly Amplified DNA Fingerprints were used to indicate the level of genetic variation within the Australian Cassia. Phenetic 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. Flowering and fruiting phenology 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. The potential impact of this insect on the ecology of Cassia brewsteri, 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.
Based on the yield data obtained in the above mentioned studies, preliminary estimates were made of return on investment from plantation culture of Cassia brewsteri for seed production. This analysis suggests that production is not economic at current yields and seed gum prices. However, production of this commodity has potential, and reconsideration at a future time is recommended. A pilot planting, perhaps installed as part of a revegetation exercise (e.g. minesite rehabilitation), would be a useful resource from which to base future assessments.
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