عنوان مقاله [English]
نویسنده [English]چکیده [English]
During the last four years (2009- 2012) several reports of forest tree decline were received, complaining about serious damage and death of many trees. The disease has been spread throughout forests of Zagross mountains which extend from north west to south west of Iran covering approximately 4,000,000 ha. Also the disease has been spread throughout forests of Alborz mountains in the north of Iran. The infected tree species included Q. brantii, Q. castaneifolia and Zelkova carpinifolia. Q. brantii Lindl. (Persian oak) has dominated in all parts of Zagros mountains from north to south, especially on the southern side of mountain in Ilam, Lorestan, Kohgilouyeh va Boyer-Ahmad, Fars and Kermanshah provinces
. Zelkova carpinifolia (Pall.) Dippel, and Quercus castaneifolia C.A.Mey are native to the Caucasus and Alborz mountains in northern parts of Iran. The decline began with browning of the leaves, viscous liquid exudatation on the branches and trunks resulting in a brown-black discoloration of bark and woody tissues. In the winter of the next year fungal growth induces a typical charcoal-black surface on diseased branches and trunks.The perithecia of B. mediterranea were observed in a black carbonaceous layer on the stem surface erupting from the declined trees and the ascospores were visible under light microscope. Perithecia were obovoid, containing, amyloid asci, with dark brown ellipsoid ascospores, with straight germ slits along the spore-length. On the basis of these morphological characteristics, the fungus was identified as Biscogniauxia mediterranea. Pathogenicity tests were conducted using an isolate of B. mediterranea on six-month-old Q. brantii seedlings using a mycelial plug of B. mediterranea colonized potato-dextrose agar and the symptoms were observed after two months and the same fungus was re-isolated.Based on previous studies infections occur in healthy living trees as endophyte and then become invasive under water stress conditions in most reports. B. mediterranea has been reported to be aggressive on drought stressed hosts. During the last ten years climate changes has occurred in Zagros forests and resulting drought stress extending desert areas followed by occurrence of the fine dust phenomenon has reduced the photosynthesis of the forest trees and making them more vulnerable to the disease. In spite of tolerance of Persian oak species to the range of temperatures from -31°C until +45, the incidence of charcoal disease has been increased dramatically on Q. brantii forests. On the basis of our current knowledge, Q. brantii represents a new host of B. mediterranea and this is the first report of Persian oak charcoal disease outbreaks throughout Zagros mountain forests of Lorestan, Ilam, Fars, Kohgiloye va Boyer – Ahmad and on Zelkova carpinfolia in Daland forests of Gorgan area.