Résumé
Aquilaria trees subjected to stress induce the formation of a transformed wood named agarwood. The formation of agarwood is a plant defense mechanism that occur in complex interactions with environmental microorganisms. Agarwood chemical compounds are mainly chromones and oxygenated sesquiterpenes such as eudesmol, agarospirol, jinkoh-eremol and valerianol, which are valued in perfumery. Its derivatives, notably the essential oil are therefore expensive. Agarwood essential oil costs 5,000 to 10,000 US $ per kg. Because of this important value and the scarcity of production from the wild, operators are planting Aquilaria and implementing various methods to induce agarwood. Many of these methods are deleterious for trees and even can alter the chemical composition of the essential oil. In this context, a consortium of farmers from French Guiana and scientists and from Centre de cooperation Internationale en Recherches Agronomiques pour le Développement (CIRAD) are developing the Aquil@Guyane project. This project aims at cultivating Aquilaria trees in French Guiana to produce agarwood of controlled chemical composition, respecting the biology and ecology of trees. In this frame we have tested the inoculation of trees with cubic and fibrous rot fungi to induce agarwood development in tree. Fungal strains used in this experiment have been isolated in the vicinity of Guianese Aquilaria plantations. Selected strains have been cultivated on wood test-sticks; infected sticks were then place in holes made with a drill in the trunks of Aquilaria. The yield of agarwood and chemical compositions of essential oils extracted from the so obtain blackened wood have been analyzed enabling to compare the different treatments. First, we evidence that the controlled inoculation of Aquilaria tree with selected fungal strains results in the production of agarwood and thus essential oils. The quality, in terms of composition of essential oils obtained among treatments was distributed between reference white wood and agarwood. The fibrous rot fungi were the most effective in terms of agarwood development and quality and yield of essential oils.