First Report of Meloidogyne enterolobii infecting melon plants in Brazil

Melon (Cucumis melo L.) is a vegetable of high economic importance in Brazil, with an average annual production of 862,387 tons (IBGE 2023). However, phytosanitary problems associated with soilborne pathogens have limited the productive potential of this crop. In October 2024, plants with stunted growth, yellowed leaves, and wilting symptoms during the hottest periods of the day were observed in commercial yellow melon production areas located in Ribeira do Amparo, Bahia (11°02'18.7"S 38°25'51.4"W). Complete plant mortality was recorded in a 2-hectare area fifty days after planting. Galls and egg masses, typical symptoms of root-knot nematode (Meloidogyne spp.) infection, were observed on the roots. Egg masses were collected and inoculated, one mass per plant of tomato cv. Santa Cruz Kada Gigante, for the purpose of obtaining a pure culture, identification, and pathogenicity tests. Morphological characterization was determined using perineal region cuts on females, revealing typical characteristics of Meloidogyne enterolobii, including an oval shape and a moderately high dorsal arch with smooth ventral striations. For molecular characterization, genomic DNA (n = 50) was extracted from females using Worm Lysis Buffer (WLB), as described by Carvalho et al. (2019). Molecular identification was performed by PCR using species-specific primers for Meloidogyne enterolobii (Long et al. 2006). Amplification of a 256 bp fragment was observed and visualized under UV light using a transilluminator (Major Science). The amplified product was subjected to Sanger sequencing (ABI 3500, Applied Biosystems). The obtained sequence was aligned in Geneious Prime version 2024.1 (Biomatters Ltd.) and compared with the GenBank database, showing 99% similarity to Meloidogyne enterolobii (accession number PV929444). To fulfill Koch’s postulates, an experiment was conducted with yellow melon (Cucumis melo var. inodorus) under greenhouse conditions. Fifteen-day-old seedlings were transplanted into 7 L pots containing autoclaved soil, sand, and substrate in a 1:1:1 ratio. Nematode extraction was performed according to the methodology described by Coolen and D’Herde (1972). Subsequently, 2,000 J2 were inoculated per pot, and the plants were maintained for 60 days. The inoculated plants exhibited characteristic symptoms similar to those observed under field conditions, whereas the control plants remained asymptomatic. According to the methodology of Oostenbrink (1966), the final J2 population was quantified by counting in a Peters chamber under a light microscope, resulting in a reproduction factor (final population/initial population) of 10.1. To the best of our knowledge, this is the first report of Meloidogyne enterolobii on melon plants in Brazil, highlighting the need for management strategies to reduce the pathogen's impact on crop production.