63 Ann. appl. Biol. (2003), 142:63-69 Printed in UK *Corresponding Author E-mail: kejayasu@sltnet.lk © 2003 Association of Applied Biologists Isolation of anti-fungal phenolic compounds from petioles of two Hevea brasiliensis (rubber) genotypes and their effect on Phytophthora meadii By K E JAYASURIYA 1 *, R L C WIJESUNDERA 2 and S A DERANIYAGALA 3 1 Department of Plant Pathology & Microbiology, Rubber Research Institute, Agalawatta, Sri Lanka 2 Department of Botany, 3 Department of Chemistry, University of Colombo, Sri Lanka (Accepted 10 October 2002: Received 11 September 2002) Summary Phenolic compounds were present in greater amounts in non-infected petioles of genotypes of Hevea brasiliensis that are resistant to Phytophthora leaf disease than in genotypes that are susceptible. Phenolic compounds extracted from petioles of either susceptible (PB86) or resistant (RRIC100) genotypes, before or after infection with Phytophthora meadii, had anti-fungal properties. Artificially infected petioles of PB86 had phenolic acids, triterpenoids or flavonoids, whereas healthy petioles contained only triterpenoids or flavonoids. However, healthy or infected petioles of RRIC100 contained only trace amounts of the above compounds and of vanillin (3-methoxy-4-hydroxybenzaldehyde). Vanillin and umbelliferone (7-hydroxycoumarin) were shown to suppress zoospore germination of P. meadii on glass slides and to inhibit its growth in pea broth and V-8 juice agar. Vanillin was slightly more active than umbelliferone. Resistance of RRIC100 to Phytophthora was suspected as being related to the polymerisation of phenolic compounds to form lignin, which may suppress further spread of the pathogen’s mycelium into healthy tissues. Formation of lignin from phenolic aldehydes as a barrier to disease spread may be a critical factor in resistance. Keywords: Plant extracts, vanillin, anti-fungal activity, Phytophthora leaf disease, rubber Introduction Major causal agents of Phytophthora leaf disease, bark rot and shoot die-back diseases of rubber ( Hevea brasiliensis Muell. Arg.) trees are Phytophthora meadii McRae, P. palmivora (Butl.) Butl., P. botryosa Chee, P. citrophthora (R.E. Sm. & E.H. Sm.) Leonian, P. nicotianae Van Breda de Haan var. parasitica (Dastur) Waterhouse and P. phaseoli Thaxter (Liyanage & Wheeler, 1989). Several copper-based fungicides are presently used in immature rubber plantations to control leaf disease and shoot die-back. However, Phytophthora diseases in mature plantations are managed by adopting protective measures, since fungicide spraying is only marginally economic. Consequently, an effective method of control is to use resistant genotypes (clones) which can tolerate the fungus both in nurseries and in the field. However, the number of H. brasiliensis genotypes that can tolerate Phytophthora diseases is limited. As in other plants, a variety of anti-fungal products is produced in H. brasiliensis close to the pathogen’s infection sites and are involved in suppressing the spread of the pathogen to healthy tissues. Scopoletin, an anti-fungal hydroxycoumarin, is known to be produced by rubber and is active against Microcyclus ulei (P. Henn) v. Arx (Garcia et al., 1995a,b). A relationship between the level of resistance of H. brasiliensis genotypes to M. ulei and the rate of accumulation of scopoletin was also observed. Production of an active blue-fluorescent compound in Hevea leaf tissues in response to infection with Colletotrichum gloeosporioides (Penzig) Penzig & Sacc. had also been observed (Tan & Low, 1975) and was later identified as scopoletin (Giesemann et al., 1986). Several other plants are also known to produce antifungal phenolic compounds, including scopoletin or umbelliferone (Modafar et al., 1993; Tal & Robeson, 1986), scoparone (Afek et al., 1986) and ayapin in Helianthus annuus L. infected by Helminthosporium carbonum Ullstrup (Tal & Robeson, 1986), and vanillic acid and p - hydroxybenzoic acid in Capsicum annuum L. stems (Candela et al., 1995). Hence, information on the effects of phenolic compounds present in rubber plant tissues to pathogens of rubber would be useful in developing disease control programmes, especially in the development of resistant clones. This paper reports the effects of vanillin and umbelliferone on the rubber pathogen P. meadii. Materials and Methods Plant material Petioles (leaf stalks) were excised from 10 trees