Stunted cotton plants (Gossypium hirsutum L. cvs. PHY 375 WR and PHY 565 WR) from two separate fields near Goldsboro in Wayne County, North Carolina were collected by the NCDA&CS Agronomic Division nematode lab for nematode assay and identification in December 2011. The galls on cotton plants were very large in comparison with those commonly associated with Meloidogyne incognita Kofoid and White (Chitwood) infected cotton. In August 2012, the lab also received heavily galled roots of soybean (Glycine max (L.) Merr. cv. 7732) from Wayne and Johnston counties. Population densities of the 2nd-stage juveniles ranged from 150 to 3,800 per 500 cc soil. Female perineal patterns were similar to M. incognita, but PCR and DNA sequencing matched that of M. enterolobii Yang and Eisenback (4). DNA sequences of ribosomal DNA small subunit, internal transcribed spacer, large subunit domain 2 and 3, intergeneric spacer, RNA polymerase II large subunit, and histone gene H3, were found to be 100% homologous when comparing populations of M. enterolobii from North Carolina and China. Species identification was also confirmed using PCR by a species-specific SCAR primer set MK7-F/MK7-R (2). M. enterolobii Yang & Eisenback was described in 1983 from a population causing severe damage to pacara earpod tree (Enterolobium contortisiliquum (Vell.) Morong) in China (4). In 2004, M. mayaguensis Rammah & Hirschmann, a species described from Puerto Rico, was synonymized with M. enterolobii based on esterase phenotype and mitochondrial DNA sequence (3). M. enterolobii is considered to be a highly pathogenic species and has been reported from vegetables, ornamental plants, guava, and weeds in China, Africa, Central and South America, the Caribbean, and Florida in the United States (1,3,4). Of particular concern is its ability to develop on crop genotypes carrying root-knot-nematode resistance genes (Mi-1, Mh, Mir1, N, Tabasco, and Rk) in tobacco, tomato, soybean, potato, cowpea, sweet potato, and cotton. Consequently, this species was added to the European and Mediterranean Plant Protection Organization A2 Alert list in 2010. Two populations of M. enterolobii one from soybean and one from cotton were reared on tomato (Solanum lycopersicum L. var. lycopersicum) in a greenhouse setting. Eggs were extracted using NaOCl and inoculated, at a rate of 7,000 per 15-cm-diameter clay pot, into a sandy soil mixture (1:1 washed river sand and loamy sand). Tomato, peanut (Arachis hypogaea L.), cotton, watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai), pepper (Capsicum annuum L.), and root-knot-susceptible and -resistant tobacco (Nicotiana tabacum L. cvs. K326 and NC 70, respectively) were transplanted immediately into the infested soil with four replications. Root galls on the host differentials were evaluated after 90 days. Reproduction occurred on all hosts except for peanut, which is consistent with reports for M. enterolobii and M. incognita race 4 (4). Adult females from pepper plants used in the host differential test were sequenced on partial 18S and ITS1 region and confirmed to be M. enterlobii. To our knowledge, this is the first report of a natural infection of North Carolina field crops with M. enterolobii.
References: (1) J. Brito et al. J. Nematol. 36:324, 2004. (2) M. S. Tigano et al. Plant Pathol. 59:1054, 2010. (3) J. Xu et al. Eur. J. Plant Pathol. 110:309, 2004. (4) B. Yang and J. D. Eisenback. J. Nematol. 15:381, 1983.