Leaf spot disease caused by Phyllosticta capitalensis on mango in Guangxi, China

Mango (Mangifera indica L.), tropical fruit renowned for its rich flavor and nutritional benefits, is extensively cultivated in southern China (Wang et al. 2023). In July 2023, leaf spots were observed in a mango plantation located in Tianyang, Guangxi, China (106°22'-107°09'E, 23°29'-24°07'N), with ~20% incidence across surveyed fields. Affected leaves exhibited 20-80% necrotic coverage, with subcircular or irregular yellowish-brown lesions gradually expanding into brown irregular areas surrounded by yellow halos. Symptomatic leaves were collected from three orchards, and 5 × 5 mm sections were excised from lesion margins and surface sterilized by immersion in 75% ethanol for 15 s and 2% sodium hypochlorite for 1 min, followed by three sterile distilled water rinses. Disinfected tissues were placed on potato dextrose agar (PDA) and incubated at 28°C under 12-h photoperiod cycles for 5 days. A total of 75 morphologically similar isolates were obtained, and three representative strains (TY6-1, TY8-1, TY9-1) were selected for characterization. Colonies displayed dark green pigmentation with granular textures and irregular white margins. Conidiomata were black, immersed or semi-immersed, subglobose to ellipsoidal, solitary or aggregated on the stroma, with circular ostioles. Conidiogenous cells appeared stick-shaped with apical constrictions, producing hyaline, unicellular, ovoid or subglobose conidia (6.0-8.5 × 8.5-13.3 μm; n=90) bearing single apical appendages. Morphological characteristics of the three isolates aligned with descriptions of Phyllosticta spp. (Wikee et al. 2013). For molecular identification, the internal transcribed spacer (ITS) region, actin (ACT), and translation elongation factor (TEF) genes were amplified and sequenced using primer pairs ITS-ITS1/ITS4, ACT-512F/783R, and TEF-728F/986R, respectively (White et al. 1990; Carbone et al. 1999). Sequences were deposited in GenBank under accession numbers PV259393-PV259395 (ITS); PV268325-PV268327 (ACT); and PV268328-PV268330 (TEF). BLASTN analyses revealed that all sequences exhibited over 99% identity with sequences (accessions JF261465, JF343647, JF261507) of the type strain of P. capitalensis (CBS 128856). Maximum likelihood phylogeny (RAxML v8.2.10) of concatenated sequences placed all isolates within the P. capitalensis clade with strong bootstrap support. Pathogenicity assays were conducted on leaves of two-year-old mango plants in a greenhouse. Both wounded and intact leaves (20 leaves/plant, 3 plants/treatment) were inoculated with 20 μL of conidial suspension (10⁶ spores/mL), while controls received 0.05% Tween 80. Plants were covered with plastic bags to maintain high humidity. After 14 days, wounded and inoculated leaves developed lesions matching field observations, whereas control and unwounded leaves remained asymptomatic. The pathogenicity test was repeated three times with similar results. Koch's postulates were fulfilled by re-isolation of P. capitalensis from symptomatic tissues, confirmed through morphological and molecular congruence. Although P. capitalensis has been reported to cause leaf spot on Hymenocallis littoralis (Wu et al. 2024) and Rubus chingii (Zhang et al. 2022), to our knowledge this is the first report of mango leaf spot caused by P. capitalensis in China. This finding provides critical insights for developing targeted management strategies against emerging mango leaf spot epidemics.