Identification And Diagnosis Of A Root-knot Nematode Infecting Papaya In Hainan Province

Root-knot nematodes (MeIoidogyne spp.) are root endoparasites that are capable of causing considerable damage on variety of crops. There are approximately 39 species of Meloidogyne spp.have been discovered in China, also Meloidogyne hispanica is discovered in Hainan, China recently. In order to assess the potential economic importance of M. hispanica and to provide control method in preventing the spread of the nematode, studies were carried out on the isozyme phenotypes, host ranges, sequence characteristics of mtDNA and rDNA loci and IGS2-RFLP detection methods of M. hispanica populations from Hainan Province.The reproduction potential of M. hispanica populations are tested on ten eultivars of seven economic crops. Biotesting revealed that tomato is good host of the M. hispanica population; watermelon and soybean are poor hosts; pepper, peanut and cotton are non-hosts. The result suggests that M. hispanica has the potential to cause economic losses in agriculture.Sequences of three mtDNA and rDNA loci were amplified from M. hispanica and the four common species M. incognita, M. javanica, M. arenaria and M. hapla, and compared between each other. Amplification products of the mtDNA COII-lrRNA region from the M. hispanica populations is about 1.8 kb in size, which is the same as M. incognita and M. javanica. Amplification products of the rDNA ITS and IGS2 regions from the M. hispanica populations were about 760 and 710 bp in size, respectively, which are similar to those from the four common species. The ITS sequence of M. hispanica showed 99.69%, 99.38%, 99.85% and 82.03% homology to those of M. incognita, M. javanica, M. arenaria and M. hapla, respectively, and the IGS2 sequence of M. hispanica was 93.31%, 93.75%, 94.32% and 57.01% homologous to those of the above four common species, respectively.A fast molecular diagnosis was developed for M. hispanica. Based on the IGS2 region differences among M. hispanica, M. incognita, M. javanica, M. arenaria, and M. hapla, RFLP was carried out on the PCR products of IGS2 region by Taq I, and a specialized 554 bp fragment from M.hispanica can distinguish it from the other four Meloildogyne species. The reliability of the diagnostic test has been validated by screening different geographic populations of four closely related Meloidogyne species. The test is fast and sensitive, it can be routinely used for direct diagnosis of a single nematode.