First report of Meloidogyne enterolobii on cotton in Brazil

Authors: GALBIERI, RAFAEL - Instituto Mato-Grossense Do Algodao (IMAMT); Davis, Richard; SCOZ, LEONARDO - Instituto Mato-Grossense Do Algodao (IMAMT); BELOT, JEAN - Instituto Mato-Grossense Do Algodao (IMAMT); Skantar, Andrea

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2020
Publication Date: 3/30/2020
Citation: Galbieri, R., Davis, R.F., Scoz, L., Belot, J., Skantar, A.M. 2020. First report of Meloidogyne enterolobii on cotton in Brazil. Plant Disease. https://doi.org/10.1094/PDIS-02-20-0365-PDN.

Interpretive Summary: A cotton field in Brazil was identified in March 2019 with plants showing reduced size, chlorosis, and root galls in a cotton cultivar with resistance to the cotton root-knot nematode, Meloidogyne incognita. The galls were noticeably larger than galls typically associated with M. incognita-infected cotton plants. Larger than expected galls on cotton had been reported for Meloidogyne enterolobii-infected cotton in the southeastern USA. The numerous large galls on an M. incognita-resistant cultivar suggested that the cotton plants found in Brazil might be infected by M. enterolobii. Soil and root samples were collected from the infested field and sent to the Nematology Laboratory of the Instituto Mato-grossense do Algodão (IMAmt) for nematode identification. The nematode was isolated and allowed to reproduce on tomato. Females were extracted from tomato roots and subjected to molecular analysis, and specimens of M. incognita and M. javanica were included for comparison. To identify the nematodes to species, we used molecular markers previously validated for Meloidogyne species identification and also DNA sequencing. The markers correctly identified all samples of M. incognita and M. javanica, whereas the unknown samples were identified as M. enterolobii, and DNA sequences matched M. enterolobii. Therefore, we conclude that the unknown Meloidogyne species found in the Brazilian cotton field was M. enterolobii. To verify reproduction on cotton, the nematode was added to individual cotton plants. Seven cotton genotypes were evaluated, 5 of which had high levels of resistance to M. incognita, and all of them were susceptible to the nematode. All seven genotypes were heavily galled with the nematode reproducing from 5.3 to 20.3 times the initial inoculum level. This is the first report of the natural infection of cotton by M. enterolobii in Brazil. Meloidogyne enterolobii is a major threat to cotton production due to the significant damage caused to the crop, the high level of reproduction, the wide host range of the nematode, and the total lack of known resistance source to this nematode in cotton. DNA was extracted from three representative females and subjected to PCR and sequencing of the mitochondrial region from COII to tRNA-His. BLAST searches against the NCBI non-redundant database yielded 100% matches to several entries from M. enterolobii.

Technical Abstract: A cotton field in Brazil was identified in March 2019 with plants showing reduced size, chlorosis, and root galls in a cotton cultivar with resistance to the cotton root-knot nematode, Meloidogyne incognita. The galls were noticeably larger than galls typically associated with M. incognita-infected cotton plants. Larger than expected galls on cotton had been reported for Meloidogyne enterolobii-infected cotton in the southeastern USA. The numerous large galls on an M. incognita-resistant cultivar suggested that the cotton plants found in Brazil might be infected by M. enterolobii. Sixty-eight samples each of soil and roots were collected from approximately 40 hectares of the infested field 90 days after planting, and the samples were sent to the Nematology Laboratory of the Instituto Mato-grossense do Algodão (IMAmt) for nematode identification. The nematode was isolated and allowed to reproduce on tomato. After 50 days, females were extracted from tomato roots and subjected to molecular analysis (10 samples with 100 females each). Specimens of M. incognita and M. javanica were included as standards. To identify the nematodes to species, we used SCAR markers previously validated for Meloidogyne species identification. In total, five pairs of markers were used. The markers correctly identified the standards as either M. incognita or M. javanica, whereas the unknown samples were identified as M. enterolobii. DNA was extracted from three representative females and subjected to PCR and sequencing of the mitochondrial region from COII to tRNA-His. BLAST searches against the NCBI non-redundant database yielded 100% matches to several entries from M. enterolobii. Therefore, we conclude that the unknown Meloidogyne species found in the Brazilian cotton field was M. enterolobii. To verify reproduction on cotton, the nematode was added to individual cotton plants 10 days after planting, and nematodes were extracted 50 days later. Seven cotton genotypes were evaluated, 5 of which had high levels of resistance to M. incognita, and all of them were susceptible to the nematode. All seven genotypes were heavily galled with the nematode reproducing from 5.3 to 20.3 times the initial inoculum level. This is the first report of the natural infection of cotton by M. enterolobii in Brazil. Meloidogyne enterolobii is a major threat to cotton production due to the significant damage caused to the crop, the high level of reproduction, the wide host range of the nematode, and the total lack of known resistance source to this nematode in cotton.