Leaf waxes and postharvest quality of Eucalyptus foliage

Abstract

Foliage characteristics and wax structure were examined in nine eucalypt species E. baueriana, E. brachyphylla, E. cinerea, E. crucis, E. gunnii, E. kruseana, E. socialis, E. tetragona and E. websteriana, in relation to consumer acceptance, production temperature and postharvest treatments. A consumer survey indicated that E. gunnii, E. cinerea, E. tetragona and E. kruseana were the most popular as cut foliage, with only E. baueriana considered unacceptable. Scanning electron microscopy (SEM) showed that all species had rod-shaped waxes, except for E. baueriana which had both rods and plates. There were significant differences between species in the length of the wax rods of mature leaves. Wax rod length increased from the youngest leaf to the tenth leaf for E. cinerea, whereas in E. brachyphylla an increase from leaf one to five was followed by a decrease from leaf five to ten. There were no significant differences between production temperatures of 24/16°C and 16/9°C on wax rod length of E. gunnii, E. kruseana, E. socialis and E. tetragona, but there were significant effects on plant height. The effects of postharvest treatments of water, 5% sucrose and 20% sucrose on wax regeneration were tested on E. brachyphylla and E. cinerea. Wax regenerated in water on E. brachyphylla but not on E. cinerea leaves, and sucrose treatments caused leaf necrosis in both species. It was concluded that careful postharvest handling and water treatment are essential for the maintenance and regeneration of the wax surface of cut eucalypt foliage.