Occurrence of Cryphonectria parasitica the causal agent of Chestnut blight in Iran

From 2001 to 2005, symptoms including dried twigs, cankers and foliar blight were observed on chestnut trees (Castanea sativa) in the Iranian forest regions of Visroud, Imamzadeh, Ebrahim, Fuman and Shafaroud, the predominant chestnut growing region of Iran. On young chestnut trees with smooth-barked branches, light-infected patches were light brown, in contrast to the olive-green colour of normal bark. On older stem infections, the discoloration was less obvious. Masses of yellow-orange to reddish-brown pustules, the size of a pin-head, developed on infected bark and exuded long orange-yellow tendrils of spores in moist weather. Fan-shaped, buff-coloured mycelial wefts formed in the inner bark and cambium. Reddish perithecia were produced in clusters of 15-20.

Bark samples were collected from the region. Examination of pustules on these samples showed very long perithecial necks that came together where they protruded through the bark. Perithecia were isolated from pustules on the samples and transferred directly to potato dextrose agar (PDA) which rapidly produced orange colored colonies. Colony pigmentation was evaluated after 7 days of growth under room light. Ascospores were 8 x 3 µm, hyaline, two-celled and constricted at the septum. Conidia exuded in yellowish tendrils, straight or slightly curved, hyaline, 2 x 1 µm. These characteristics permitted the identification of the fungus as Cryphonectria parasitica (Griffin et al., 1978; Jaynes et al., 1980; Hanlin, 1992).

Pathogenicity tests were conducted on 6 month-old chestnut plants. These plants were cut with a sterile scalpel and inoculated with 5-mm mycelial disk from a 7-day old pure culture of fungal pathogen. The inoculation site was covered with parafilm (to prevent pathogen inoculum from drying) and the plants were maintained at 25-28°C. Control plants were treated with sterile distilled water. Plants were examined for disease symptoms weekly. After 6 weeks all chestnut plants inoculated with the fungus died, with pronounced necrosis at the inoculation point. Sampling from the necrotic woody tissues, 1 cm above the inoculation point, resulted in the re-isolation of the fungus. No fungus was isolated from the control plants.

To our knowledge this is the first report of C. parasitica causing chestnut blight in Iran.