In South Africa, the genus Eucalyptus plays an important role as a plantation tree and hence forms a major economic component in the forest sector. An insect pest of these Eucalyptus species, Gonipterus scutellatus, causes periodic defoliation in the plantations. Plants have extraordinary array of chemicals (secondary metabolites), which defend them from herbivores. This study reports on the seasonal variation of the tannin concentration and carbohydrate content of the leaves of nine Eucalyptus species. Soluble tannins were quantified using Hagerman test and the carbohydrate content with a refractometer. Generally high tannin concentrations were observed during spring and late summer with low concentrations during autumn and winter. During the months of February, April, July tannin concentration was usually found to be higher than the carbohydrate content. The higher concentration of tannin could be linked to the allocation of carbon for the production of tannin instead of carbohydrates for growth.
Dissertation (MInst Agrar)--University of Pretoria, 2006.