Cryphonectria parasitica in Sessile Oak in Hungary

Abstract

Since 1999 occurrence of chestnut blight fungus (Cryphonectria parasitica) has been observed in sessile oak in Western and South-Western regions of Hungary in young and middle aged Quercus petraea stands mixed with Castanea sativa. Incidence and impact of the disease, vegetative compatibility type diversity of the pathogen, occurrence of the natural hypovirulence in oak, conversion capacity of the local hypovirulent strains and development of the symptoms in inoculated oak trees were studied in order to investigate the conditions of the biological control based on the hypovirulence in oak. In 2003 survey plots were designated in 12 infected oak stands. The rate of infection varied up to 23.02% and the mortality rate up to 5.76%. Isolations were performed in 2004 from survey plots and in 2006 from larger areas of two forest management units. In 2004 all isolates from oak were of virulent character, while 15.38% of the isolates showed hypovirulent features in 2006. Totally 15 VC types were delimited among the 174 isolates. The VC type diversity varied between 1 to 5 types/plot or forest subcompartment. Five local hypovirulent isolates showed full conversion capacity to the selected virulent strains of different VC types in vitro. Early appearing and progressive increasing of the symptoms were observed in the oak trees inoculated with virulent strains, however more than half of the trees healed during the second year after the inoculation. Some hypovirulent inoculations caused superficial altering of the suberisation, showing the establishment of the hypovirulent fungus in the bark. Our results show favourable conditions for successful application of the preventive control by disseminating the hypovirulent strains in young oak stands.