Proceedings of The Fourth International Iran & Russia Conference 1048 Phenolics in the seed coat of oriental beech (Fagus orientalis lipsky) as an autotoxic factor Ali Soltani Faculty of Agriculture, ShahreKord University, P.O.Box 115 – ShahreKord; Fax: 0381- 4424428, Email: soltani@agr.sku.ac.ir Abstract The aim of this article is to give adequate reasons to explain germination improvement of oriental beech (Fagus orientalis) seeds and acceleration of dormancy breakage due to endocarp removal. The results showed that the endocarp surrounding oriental beech seeds did not restrict water imbibition, i.e. both nuts and seeds were fully imbibed after 72 h. Quantification using half-strength Folin-Ciocalteu reagent and UV spectroscopy revealed a significant higher exudation of phenolics in seeds in compare with nuts (seeds with endocarp) during cold wet stratification. On the other hand germination of radish seeds was suppressed with 10-5 M GAE concentration of this extract. Total water-soluble phenolics in the seed coat were quantified to be 0.72 mg gallic acid equivalents (GAE) per gram dry weight. Gallic acid, p-hydroxybenzoic acid and, hydroxycinnamic acid were the main phenolics in the water extract of seed coat which were qualified as phenolics with toxic property, using GC-MS. It was speculated that the high concentration of phenolics of seed coat in the endocarp cavity after imbibition, inhibits germination or delay dormancy breakage of beech seed, which make the seed of this species with two dormancy mechanisms, physiologic and seed-coat induced. Scarification or removal of the endocarp therefore, potentiates the stimulatory effect of cold moist stratification on germination of oriental beech nuts. Key Words: allelopathy, autotoxicity, oriental beech, seed germination, seed dormancy, phenolics Introduction Hyrcanian forests of oriental beech (Fagus orientalis Lipsky) in Iran is mainly managed as shelterwoods relying mainly on natural regeneration (Anonymous, 1994). However, regeneration is unsatisfactory (Sagheb-Talebi & Schütz, 2002) and enrichment planting is usually necessary to obtain an optimal number of seedlings in the regeneration areas (Teissier du Cros, 1984). Seedling production is hampered by the poor viability and deep dormancy of the nuts at the time of dispersal and local nurserymen consider at least 5 - 8 weeks of cold moist stratification to overcome the dormancy (Rezaie & Naseri, 1999). Any progress involving seed dormancy breakage can effectively facilitate seed germination in nurseries and shorten the seedling production time, thereby increasing regeneration success. In European beech (F. sylvatica L.), closely related to oriental beech (Gömöry et al., 1995), abscisic acid (ABA) is considered a key compound in maintaining embryo dormancy and it has been shown that dormancy release involves an increased metabolism of ABA in the embryo (Le Page-Degivry et al., 1997). This dormancy can be regulated by environmental factors and seed handling methods (Côme & Thévenot, 1982; Poulsen, 1992; Thomsen, 1997). Nuts of oriental beech (Soltani, unpublished data) and European beech (Suszka et al. 1996) also show a high degree of polymorphism in dormancy release even within the same lot exposed to the same environmental conditions, implicating that the dormancy mechanisms in this genus may not only depend on the physiological dormancy caused by ABA. For European beechnuts, Thomsen (1997) and Shen & Odén, (2002) have shown that germination capacity is amplified by mechanical scarification of the endocarp (the hard pyramidal inner layer of the pericarp, which covers the seed) and the same results for oriental beechnuts were obtained when endocarps were manually removed (Soltani et al. unpublished data). Reasons for this may be that imbibition of water is restricted by the endocarp and/or other dormancy-inducing or germination- inhibiting substances are present in tissues surrounding the embryo, which can be leached out or oxidized by removing the endocarp. The presence of biochemical inhibitors associated with seed structures is widespread in the plant kingdom (Levi-Minzi et al., 1994). There are reports on numerous secondary compounds in plants with allelopathic properties, among them phenolics found in testa or pericarp of several species (Guenzi &