Mulberry Damages Caused by a Root-Knot Nematode, Meloidogyne mali Indigenous to Japan
A root-knot nematode, Meloidogyne mali was described by Itoh et al. (1969) as a new species infecting apple roots in Japan. Any incidence caused by this species has not been recorded in other countries since then. It was first considered that M. mali distributed only in the northern part of Japan and it was parasitic to woody plants. M. mali has been regarded as one of the most important nematodes injuring apple trees in Japan. It is now recognized that this nematode distributes in most of the mulberry fields throughout Japan, parasitizing mulberry as well as several kinds of herbaceous plants including vegetables. An analysis of mulberry damages caused by M. mali indicated that the growth of seedlings and graftings of mulberry inoculated with more than 2,500 of the second stage larvae of M. mali was significantly inferior to that of the control trees without inoculation. One year after the inoculation, 30-60% of those trees infected by nematodes were dead. In 2-3 year-aged mulberry trees inoculated with nematodes, they reduced their leaf weight by 10-20%. The symptom caused by the nematode infection came out more slowly and the damages were smaller as compared with those in younger trees.