First Report of the Root-Knot Nematode <i>Meloidogyne enterolobii</i> Parasitizing <i>Pithecellobium dulce</i> in Mexico

The guamúchil, or Madras thorn (Pithecellobium dulce Roxb. Benth) is a thorny, evergreen tree approximately 20 m tall that belongs to the family Fabaceae. It is a fast-growing species, highly adaptable to drought conditions, thriving in poor soils, and native to the Americas, ranging from Mexico through Central America, Colombia, and western Venezuela (Hernández-Neri et al. 2021; Abdullah et al. 2023). In Mexico, it is used in traditional medicine, for human consumption (fruit), as fodder for cattle and goats, in the production of handicrafts, as an ornamental species, and for green manure (Hernández-Neri et al. 2021). In August 2024, guamúchil trees exhibiting galls on roots were found in Santa Maria Jalapa del Marques, Oaxaca, Mexico. The gall incidence was approximately 50% (20 diseased trees). The roots were washed with tap water, and females and egg masses were obtained by dissecting galls. Microscopic analysis of the perineal pattern in mature females (n=10) revealed a round to ovoid shape, with a high dorsal arch and nearly square-shaped. The females (n=25) exhibited a globular to pear-shaped body, measuring between 598.3 and 789.5 µm in length and 445.1 to 587.8 µm in width. The stylet ranging from 14.8 to 15.9 μm in length, with dorsally curved cone, rounded knobs, and the distance from the stylet base to the dorsal gland orifice (DGO) ranged from 4.4 to 5.6 µm. The distance of the excretory pore to the head end was 41.4 to 73.1 µm. These morphological features align with those previously described for Meloidogyne enterolobii (Yang and Eisenback 1983; Salazar-Mesta et al. 2023). For molecular analysis, genomic DNA was extracted from individual adult females, and a fragment of the mitochondrial cytochrome c oxidase subunit I (coxI) gene was amplified by PCR using the primers pair JB3/JB5 (Bowles et al. 1992). The sequence was deposited in GenBank under the accession number PQ489252. BLASTn searches of the sequence exhibited 100% identity with coxI sequences OR965000 and OR965003 of Meloidogyne enterolobii in butternut pumpkin (Cucurbita moschata) and snake bean (Vigna unguiculata) from Australia, respectively. For phylogenetic reconstruction, Bayesian inference and maximum likelihood analyses were performed, which grouped isolate MeGUA01 within the same clade with other isolates of M. enterolobii. Pathogenicity tests were conducted by inoculating 5,000 eggs of M. enterolobii onto each of 10 healthy guamúchil seedlings (30-day-old) grown in pots with sterilized soil. Three non-inoculated seedlings were used as controls. Plants were maintained in a greenhouse at 20 to 35 °C for 5 months. Stunted growth and root galling were observed on inoculated plants, whereas control plants remained symptomless. The nematode reproduction factor was 13.4 at 5 months after inoculation. The nematodes recovered from inoculated roots were morphologically identical to those observed in naturally infected roots. Previously, only M. incognita had been identified parasitizing P. dulce in Saudi Arabia based on morphology (Sherbiny 2011). To the best of our knowledge, this is the first report of the root-knot nematode M. enterolobii parasitizing guamúchil in Mexico and worldwide. This report expands the host range of this nematode, highlighting the need for further studies to determine its distribution on other host crops, including solanaceous species as well as other economically important fruit crops.