Essential Oil of Eaglewood Tree: a Product of Pathogenesis

Journal of Essential Oil Research: JEOR, Nov/Dec 2005 by Tamuli, Phatik, Boruah, Paran, Nath, Subhan C, Leclercq, Piet

Abstract

The essential oil of eaglewood tree (Aquilaria agallocha Roxb.) has been considered to be a pathological product. An investigation was carried out to study the difference in composition of oils obtained from healthy, naturally infected and artificially inoculated eaglewood using GC and GC/MS analyses. This investigation showed a marked difference in the oil compositions among the treatments with regards to their quality. Valerianol (3.0%) and tetradecanioc acid (7.1%) contents were recorded higher in the oils of naturally infected plants than in that of healthy ones (0.1% and 6.9%, respectively). Pentadecenoic acid was totally absent in the oils of healthy, whereas it was found in a greater amount (6.8%) in the oil of naturally infected plants. In contrast, dodecanoic acid (3.1%), pentadecanoic acid (6.2%), hexadecanoic acid (31.5%) and octadecanoic acid (4.1%) were found in a higher amount in the oils of healthy plants, while the oils obtained from naturally infected plants contained lower amounts of these components (2.5%, 4.8%, 20.0% and 1.0%, respectively). The oils obtained from the inoculated plants showed almost similar distribution of the components with healthy plants.

Key Word Index

Aquilaria agallocha, Chaetomium gtohosum, Fusarium oxysporum, Thymelaeaceae, essential oil composition, hexadecanoic acid.

Introduction

The eaglewood tree Aquilaria agallocha Roxb. (syn. Acquilaria malaccensis Lamk., family: Thymelaeaceae) is a precious floral wealth of India (1). The resinous patches of fragrant wood of the plant known as 'agar' is used as incense in Egypt, Arabia, and throughout the northeast part of India where it can be found. The oil obtained from agar is described as a stimulant, cardiatonic and carminative. It is also used in the cosmetic and pharmaceutical industries. Agar is considered to be a pathological product produced by fungal invasion of the host (2). Since 1938, few workers have been studying about agar formation and reported the agar zones to be associated with mold and decay fungi (3-11). Association of mycoflora in the seed, rhizosphere and phyllosphere were studied by Tainuli et al. (12-14). Among different fungal species reported to be associated with agar zones, few could exhibit pathogenesis with the development of disease symptoms while others seem to be of saprophytic nature in different eco-geographical conditions. Studies on the oil of infected A. agallocha were made by various workers (15-26). Maheshwari et al. (15) isolated three newsesquiterpenic furanoids of the selinane group from aganvood oil, obtained from the fungus infected plant and their structures and absolute configurations determined by degradative studies and physical measurements. Varma et al. (16) examined that degradative studies and physical measurements supported by an unambiguous synthesis of the derived ketone have led to the assignment of a novel spiro-skeleton to agarospirol, a sesquiterpene alcohol isolated from the essential oil of infected aganvood. Paknikar and Dhavlikar (17) and Paknikar and Naik (18) reported that on hydrogenation of α-agarofuran and β-agarofuran the same dihydroagarofuran was obtained. Thomas and Ozainne (19) used a combination of hydrogenation, ^sup 1^H-NMR, ^sup 13^C-NMR and some naturally occurring dihydroagarofuran and isodihydroagarofuran to unequivocally show that the dihydroagarofuran found was indeed dihydro-β-agarofuran and isodihydroagarofuran was isodihydro-β-agarofuran; two separate compounds.

Pant and Rastogi (20) and Bhandari et al. (21) isolated a new sesquiterpene, agarol and a couinarinolignan, aquillochin, respectively, from the oil of Aquilaria agallocha. Nakanishi et al. (22) showed that a benzene extract of aganvood collected in Indonesia contained a new tricyclic sesquiterpene alcohol as a major constituent. Nagashima et al. (23) further characterized the presence of two more sesquiterpene alcohols, jinkohol II and jinkoh-eremol, from the same Indonesia agarwood oil. Nakanishi et al. (24) again reported that a benzene extract of an Indonesian sample of 'Jinkoh' agarwood was found to contain α-agarofuran, 10-epi-γ-eudesmol and oxo-agarospirol. Ishihara et al. (25) characterized seven new sesquiterpenes based on the guaiane skeleton in a sample of agarwood oil. Five new eudesmane sesquiterpenes and three other compounds further characterized by Ishihara et al. (26) in a sample of agarwood extract produced in the laboratory from A. agallocha of Vietnamese origin.

Vesicular-arbuscular myccorhizal association in the tree species and changes in amino acid composition due to pathogenesis were also studied by Tamuli et al. (27,28). So far the qualitative study of the oils of healthy and infected eaglewood has yet to be investigated. The present investigation was, therefore, undertaken to study the qualitative differences in the oils obtained from healthy, naturally infected and artificially inoculated eaglewood.

Experimental

Artificial inoculation of fungal isolates: The most frequently isolated fungi from infected agarwood (e.g. Chaetomium globosum and Fusarium oxysporum) were inoculated to the healthy plants by artificial boring on to the plants (9). Inoculation was made with two different fungi alone and in their combination. Observations were made at an interval of 30 days after inoculation.