Nematode-Induced Pine Wilt Disease: Factors Influencing Its Occurrence and Distribution

Abstract

Abstract Bursaphelenchus xylophilus, pinewood nematode, and B. mucronatus are members of the pinewood nematode species complex (PWNSC) from forested areas of the northern hemisphere. In the presence of suitable vectors, pathogenic forms of the PWNSC cause pine wilt disease in susceptible tree species in very warm climates. Pine wilt disease is expressed rarely in the northern hemisphere outside of Japan and south China. The disease is expressed only where susceptible pines have been introduced into environments warmer than their natural climatic range, or where pathogenic isolates of the PWNSC have been introduced into warm climates containing susceptible tree species. It is probable that the pine wilt epidemic in Japan is a result of a pathogenic form of the PWNSC being introduced around the turn of the century. Pine wilt disease has not been recorded for any part of North America, Europe, or Asia where mean daily summer temperatures are 20°C or below regardless of the presence of susceptible trees or pathogenic PWNSC isolates. Some PWNSC isolates from northern regions of Europe and North America move and reproduce more rapidly at lower temperatures than do PWNSC isolates from warmer climates. These characteristics may be factors that contribute to the differences in pathogenicity of different isolates of the PWNSC to different pine species. For. Sci. 36(1):145-155.