Diversity and distribution of alien fungal pathogens causing damages on Pinus spp. in South Bulgaria.
The diversity and distribution of alien fungal pathogens causing damages on Pinus spp. in South Bulgaria were evaluated in the period of 2017-2018 in 20 sample plots established on the territory of 8 Regional Forest Directorates (RFD). The identification of invasive species was based on the assessment of trees' health status, recovering the symptoms of diseases and damages on needles, cones, shoots, branches and roots. Ten natural and introduced Pinus spices were studied for the presence of fungal pathogens. Diseases caused by the invasive alien pathogens Diplodia sapinea, Dothistroma septosporum, Dothistroma pini and Lecanosticta acicola were determined. The harmful impact of established pathogens was assessed according to their virulence and aggressiveness, the degree of tree crown defoliation and discolouration, physiological condition of host plants and the rate of disease spreading. Among the established pathogens, the most common and widespread were Diplodia sapinea caused shoot blight diseases on all studied Pinus spp. The current high existence of D. sapinea outbreaks contributed considerably to physiological weakness of established pine trees and they became more susceptible to attack by aggressive xylophages. The most aggressiveness virulent pathogens were the invasive species Dothistroma septosporum and Lecanosticta acicola caused red and brown needle blight disease, tree dieback and degradation of forest landscape at sites between 700 and 800 m a.s.l, with high air humidity required for spore release and spreading of the diseases.