First Report of Curvularia eragrostidis Causing Leaf Spot on Jackfruit ( Artocarpus heterophyllus ) in China

Abstract

Jackfruit (Artocarpus heterophyllus Lam.) is an economically important fruit tree widely cultivated in tropical and subtropical regions (Gupta et al. 2023). In July 2025, a leaf spot disease was observed on jackfruit trees in Zhanjiang, Guangdong Province, China. Diseased leaves initially developed small brown necrotic spots that gradually enlarged and coalesced, resulting in leaf yellowing and premature defoliation. Field surveys indicated that the disease was present in approximately 25% of the surveyed orchards. Symptomatic leaf tissues collected from diseased plants were surface-disinfested in 70% ethanol for 30 s, followed by 1% sodium hypochlorite for 1 min, rinsed five times with sterile distilled water, and plated onto potato dextrose agar (PDA). After incubation at 28°C in the dark for 5 days, 16 fungal isolates with similar morphological characteristics were obtained. Colonies exhibited an average radial growth rate of 17.1 ± 1.6 mm day⁻¹. Conidiophores were septate, pale brown, simple, smooth, straight to slightly curved, exhibiting sympodial proliferation and often bearing clusters of conidia at the apex. Conidia were solitary, ellipsoidal to oblong, straight or slightly curved, pale to dark brown, mostly 3-distoseptate, with a conspicuously darkened median septum and paler terminal cells. Conidia measured 16.3–30.9 × 5.6–11.2 μm (mean ± SD = 21.8 ± 4.9 × 8.1 ± 1.6 μm, n = 50), consistent with descriptions of Curvularia eragrostidis. For molecular identification, the internal transcribed spacer region (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and translation elongation factor 1-alpha (TEF1-α) genes of three representative isolates (LNU-16, LNU-17, and LNU-18) were amplified using primer pairs ITS1/ITS4 (White et al. 1990), GDF/GDR (Templeton et al. 1992), and EF1-983F/EF1-2218R (Rehner and Buckley 2005), respectively. The obtained sequences were deposited in GenBank (ITS: PZ528505–PZ528507; TEF1-α: PZ538484–PZ538486; GAPDH: PZ538487–PZ538489). BLASTn showed 100% ITS identity with C. eragrostidis TD4.2 (OR135782), 100% GAPDH identity with C. eragrostidis RU1 (PQ442766), and 99.77% TEF1-α identity with C. eragrostidis CD15 (MK886803). Maximum-likelihood analysis of concatenated ITS, GAPDH, and TEF1-α sequences placed the three isolates within the C. eragrostidis clade. Based on morphology and multilocus analyses, the pathogen was identified as C. eragrostidis (Gan et al. 2018). Pathogenicity tests were conducted on healthy detached jackfruit leaves. Leaves were surface-disinfested with 0.1% sodium hypochlorite and rinsed three times with sterile distilled water and allowed to air dry. A conidial suspension (10⁶ conidia mL⁻¹) prepared from a 12-day-old culture was sprayed onto leaves. Control leaves received sterile distilled water. Ten leaves were used for each treatment, and the experiment was repeated twice. Inoculated leaves were maintained at 25°C and 80–85% relative humidity. Seven days after inoculation, brown lesions surrounded by chlorotic halos developed on all inoculated leaves and were similar to those observed under field conditions, whereas no symptoms were observed on control leaves. The fungi reisolated from the inoculated leaves were identified as C. eragrostidis through morphological examination and sequence analyses of ITS, GAPDH, and TEF1-α, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of Curvularia eragrostidis causing leaf spot on jackfruit in China. This finding expands the known host range of C. eragrostidis and provides a basis for future studies on disease epidemiology and management.