9Ferris V R, Ferris J M, Faghihi J. Variation in spacer ribosomal DNA in some cyst-forming species of plant-parasitic nematodes. Fundamental and Applied Nematology, 1993. 16:177～184.
10Vrain T C, Warkarchuk D A, Lévesque A C, et al. Intraspecific rDNA Restiction Fragment Length Polymorphism in the Xiphinema americanum group. Fundamental and Applied Nematology 1992. 15:563～573.
