First Report of the Root-Knot Nematode Meloidogyne enterolobii Parasitizing Eggplant in Mexico.

Eggplant (Solanum melongena L.) is an important vegetable cultivated in Mexico and the state of Sinaloa is the largest producer of eggplants with 90% of the country's total production. In April 2022, eggplants cv. Barcelona exhibiting root-knot, stunted growth, and yellowing were detected in a greenhouse in Culiacán, Sinaloa, Mexico. Disease incidence was approximately 10% (1000 plants evaluated). Ten soil samples were collected from the greenhouse. An average of 400 root-knot nematode second-stage juveniles (J2s) were extracted from 100 g of soil for each sample. Roots were washed with tap water and dissected. Females and egg masses were obtained by dissecting galls. Microscopic examination of the perineal pattern of mature females (n= 10) was round to ovoid, with rounded and high dorsal arch. Females (n= 20) were globular to pear-shaped, body length of 645 to 739 µm, body width of 470 to 559 µm; the stylet was dorsally curved, 15.1 to 16.2 µm long, and with rounded stylet knobs; neck length of 195 to 202 µm and the distance from the base of the stylet to the dorsal gland orifice (DGO) was 4.2 to 5.8 µm. Second-stage juveniles were vermiform, annulated, and tapering at both ends. Morphological characteristics of the females and J2s were consistent with those reported for Meloidogyne enterolobii (Yang and Eisenback 1983). For molecular identification, total DNA was extracted from individual females according to the extraction protocol described by Hu et al. (2011), and the ribosomal intergenic spacer 2 (IGS2) was amplified by PCR using the specific primers Me-F/Me-R for M. enterolobii (Long et al. 2006). PCR amplification generated a 236-bp fragment for the analyzed sample and the amplicon was sequenced. The sequence was deposited in GenBank under the accession number OP004802. BLASTn searches showed 100% identity with available sequences of M. enterolobii from the USA (MH800967) and China (KP411228, MT742011). A phylogenetic tree including published IGS2 sequences for Meloidogyne spp. was constructed based on Maximum Likelihood method. The phylogenetic analysis placed the sequence MeCUB in the same clade with Meloidogyne enterolobii. Pathogenicity tests were performed under greenhouse conditions by inoculating 5000 eggs of a pure population of M. enterolobii on 10 healthy eggplants cv. Barcelona (30-day-old) grown in pots with sterilized soil. Five uninoculated eggplants were used as control. Plants were maintained at 26 to 34°C in a greenhouse for 35 days. Stunted growth and root-galling symptoms appeared on inoculated plants after 21 days, whereas control plants remained symptomless. Nematode reproduction factor (final population density/initial population density) was 0.93 and 2.28 at 28 and 35 days after inoculation, respectively. The nematode on the inoculated roots was morphologically identical to that observed on naturally infected roots in the field. The pathogenicity test was carried out twice with similar results. Meloidogyne enterolobii has been previously reported on eggplants in Puerto Rico (Rammah and Hirschmann 1988). To our knowledge, this is the first report of M. enterolobii causing root-knot of eggplant in Mexico. This nematode is widely distributed in Sinaloa affecting other vegetable crops such as tomato (Martínez-Gallardo et al. 2015), chili (Carrillo-Fasio et al. 2020), and cucumber (Gómez-González et al. 2020), so future studies are required to evaluate integrated management strategies.

First Report of Soft Rot of Pitahaya Fruit Caused by Gilbertella persicaria in Mexico.

Pitahaya (Hylocereus spp.), also called dragon fruit, is a cultivated cactus that is native to Mexico as well as Central and South America. In September 2021, soft rot of fruit of H. ocamponis, H. undatus, and H. costaricensis was observed in a commercial orchard located in La Cruz de Elota, Sinaloa, Mexico. The disease occurred on approximately 15% of pitahaya fruit. Lesions on fruits were water-soaked and light brown, extending to the whole fruit and covered with mycelia, sporangiophores, and sporangia. Colonies of a fungus were consistently isolated on PDA medium and 10 isolates were obtained. Three isolates were selected and deposited in the Culture Collection of Phytopathogenic Fungi at the Research Center for Food and Development (Culiacán, Sinaloa) under accession nos. CCLF171-CCLF173. Colonies on PDA medium were initially white and later grayish. Sporangiophores were hyaline to light brown, and aseptate. Sporangia (n= 30) were initially light brown but became black at maturity, globose to subglobose, single, terminal, 65.8 to 117.2 µm in diameter, and longitudinally separated into two halves. Columellae (n= 20) were light brown, obovoid, 33.5 to 72.9 × 31.5 to 69.8 µm, with a distinct basal collar. Sporangiospores (n= 100) were hyaline, globose to ellipsoid, aseptate, 6.9 to 12.8 × 5.1 to 10.9 µm, with polar appendages. Chlamydospores were solitary or in chains, oval or irregular. Zygospores were not observed. Based on the morphological characters, the fungal isolates were identified as Gilbertella persicaria (Benny 1991). To confirm the identity, total DNA was extracted, and the internal transcribed spacer (ITS) region was amplified by PCR using the primers ITS5/ITS4 (White et al. 1990), and sequenced. The ITS sequences were deposited in GenBank under the accession nos. OM301904-OM301906. A BLASTn search of these sequences showed 99.47 to 99.81% identity with the sequence MK301174 of G. persicaria from Hylocereus sp. in Taiwan. A phylogenetic analysis based on Maximum Likelihood method grouped the isolates CCLF171-CCLF173 within the G. persicaria clade. Pathogenicity of the three isolates was verified on healthy Hylocereus spp. fruit. Fruit of H. ocamponis, H. undatus, and H. costaricensis were surface sterilized with 80% ethanol, and dried. For each fungal isolate, five detached fruits were superficially wounded with a sterile toothpick and inoculated by placing 15 µL of a spore suspension (1 × 105 sporangiospores/mL). Sterile distilled water was applied to five healthy pitahaya fruits to serve as controls. All fruits were kept in a moist plastic chamber at 25°C and 12 h light/dark for 6 days. All inoculated fruits developed rot 3 days after inoculation, whereas no symptoms were observed on the control fruits. The experiment was repeated twice with similar results. The fungi were consistently re-isolated from the diseased fruits, fulfilling Koch´s postulates. Gilbertella persicaria has been previously reported to cause stem rot, fruit rot, and wet rot in pitahaya (Hylocereus spp.) in Japan (Taba et al. 2011), China (Guo et al. 2012), and Taiwan (Lin et al. 2014), respectively. To our knowledge, this is the first report of G. persicaria causing soft rot of Hylocereus spp. fruit in Mexico. Additional studies are needed to develop effective disease-management strategies.