Natural dissemination of hypovirulent Cryphonectria parasitica strain used for biological control of chestnut blight

Abstract

Chestnut blight, caused by Cryphonectria parasitica Murr. Barr, is the most serious disease of chestnut trees in Turkey onwhich several studies related to biological control were conducted. The aim of this study was to determine the cause of the occurrenceof healing cankers on untreated chestnut trees and the role of carriers in the spread of hypovirulence by laboratory tests, and to discoverthe effect of some environmental factors (temperature and relative humidity) on the natural spreading of hypovirulence. The studywas carried out in a chestnut grove where biological control studies of the disease had been performed in previous years. Bark sampleswere collected from healed cankers and 388 possibly hypovirulent isolates were obtained. Two of them that were white convertedvirulent isolates to hypovirulent ones, but others developed yellowish cream-colored mycelia and did not convert virulent isolates.dsRNA analysis was performed on randomly selected possible hypovirulent isolates collected from healed cankers. After the virusconcentration had increased, dsRNA-positive reactions were obtained for 56.73% of the isolates. Thirty-one possible hypovirulentisolates from Formicidae and Gastropoda did not convert virulent isolates to hypovirulent ones. dsRNA analysis was performed onthese isolates and 61.29% of them containing dsRNA were observed in the invertebrates collected from cankers that had healed fromhypovirulence. It was also observed that there was no significant difference among the date of average temperatures and date of relativehumidity from 3 different altitudes. It was determined that the reason for the occurrence of the healed cankers on untreated trees wasthe natural dissemination of hypovirulence, ants and snails might have played a role in the natural dissemination of hypovirulence, andhealed cankers mostly occurred on the western sides of shaded slopes.