Armillaria mellea as a cause of oak decline in Hatam-baigh forest of Iran.

A200 ha forest of "Hatam-baig" is located in Ardebil Province on the Northwest of Iran. Oak trees (Quercus macranthera Fisch & Mey) in this forest have been faced with declining and extinction since 1991, that has destructed about one third of the forest trees until now. This disorder was expressed in various symptoms including wilting, defoliation and decline. In order to identify factors causing decline, a study was managed from 1998 to 2001. Samples were taken from roots, trunks, crowns and soil beneath the canopy and were cultured on different culture media subsequently. Armillaria mellea (Vahl) P. Kumm., Phytophthora cryptogea Pethybr. & Laff., Dematophora sp., Pythium aphanidermatum (Edson) Fitzp. and Fusarium spp. were the most common isolated fungi. A. mellea appeared to be the essential causal agent of the decline according to the studies made on oak tress decline around the world and based on brown rot observed beneath mycelial fans in the cross section prepared from the trunk and characteristics of the isolated fungi. The fungus activity had been favored by physiological weakness and stresses in oak rootstocks caused by brown- tail moth (Euproctis chrysorhoea L.) and drought stress in infected trees. The biological species of this fungus was identified as Armillaria mellea, using hybridization tests and application of haploid test strains. The fungi such as Phytophthora sp., Pythium sp., and Dematophora sp. can not be infective in this forest due to being hydrophylous. In the southern part of the forest with remarked steepness, the severity of the decline appears to be more than that in the smoothly northern part. The decline of Q. macranthera is reported as matrix nova. The report of the isolated fungi from this oak species is also universally new.