تنوع مورفولوژي و قدرت بيماري زايي جدايه هاي مختلف Cryphonectria parasitica عامل بيماري سوختگي شاه بلوط در استان گيلان

STUDY ON THE MORPHOLOGICAL AND VIRULENCE VARIABILITY OF Cryphonectria parasitica CAUSAL AGENT OF CHESTNUT BLIGHT IN GUILAN PROVINCE, IRAN

To study morphological and virulence variability of Cryphonectria parasitica isolates in Guilan province, the only region with important chestnut (Castanea sativa) stands in Iran, several collections were made from chestnut stands located in Shaft, Resvanshahr and Lahijan regions during 2006-2007. One hundred twenty single spored isolates were obtained. After primary evaluation based on colony morphology and growth rate 15 isolates, which some of them were resemble to hypovirulent isolate, were selected for more studies. These isolates were investigated for colony morphology, laccase activity, apple fruit rot, pathogenecity on cut stems and natural sprouts in forest. Isolates showed differences for some characteristics. Growth rate was 30-87 mm after 7 days on PDAmt at 25 C° in different isolates. Colony color ranged from yellowish orange to brownish orange to white. Laccase activity on Tannic Acid Malt Agar media at 22 C° and dark condition was different. Virulance of isolates on apple fruit, cut stems and natural sprouts showed significant differences. According to these results three isolates were determined as hypovirulent races. This is the first record of probable occurrence of hypovirulent isolates of Cryphonectria parasitica in Iran. These isolates would be good candidate for biological control of the disease in this region.