Characterization of <i>Alternaria gossypina</i> associated with <i>Ormosia hosiei</i> seedlings leaf blight disease in Guizhou Province, China

Ormosia hosiei Hemsl. &amp; E. H. Wilson, one of the Chinese endemic legume trees, possesses significant economic, medicinal, and ornamental values (Dai et al. 2023). In September 2025, leaf blight symptoms were observed on O. hosiei seedlings in a forest nursery located in Guiyang City, Guizhou Province, China (26.38°N, 107.37°E), with a disease incidence of approximately 47% (n = 300). Initially, brown discoloration and drying appeared on the leaf tips. The symptomatic tissue continued to expand basipetally. Twelve leaves with drying symptoms were collected for pathogen isolation. Symptomatic leaf tissues (5 × 5 mm) were excised from infected margins, surface sterilized sequentially with 1% sodium hypochlorite (30 s) and 75% ethanol (60 s), rinsed three times in sterile water, air-dried, and plated on potato dextrose agar (PDA) medium. Cultures were incubated at 25°C under dark conditions for 3 d. Sixteen isolates showed similar morphology on PDA with dense light brown mycelia. The conidia were brown and contained 2-septate rod spindle (longitudinal septate connection between two transverse septates), averaging 25.1 × 8.2 μm (n = 30) and the crossed septum was ovoid, averaging 17.6 × 19.3 μm (n = 30). These morphological characteristics were consistent with Alternaria sp. (Woudenberg et al. 2013). For molecular identification, genomic DNA from a representative isolate YK1-24 was used to amplify and further sequence three loci: the internal transcribed spacer (ITS) region using primers ITS1 and ITS4 (White et al. 1990), the Alternaria major allergen gene (Alt a 1) using primers Alt-for and Alt-rev (Woudenberg et al. 2015), and the large subunit (LSU) using primers LROR and LR5 (Vilgalys and Hester 1990). BLASTn analysis revealed that the ITS, Alt a 1 and LSU sequences of isolate YK1-24 had 100% (548/548), 100% (479/479), and 100% (852/852) sequence identity to the ex-type strain A. gossypina (PX048794, PP057865, OR272091), respectively. Sequences from isolates YK1-24 were deposited in GenBank (ITS: PX670549, Alt a 1: PX677460, LSU: PX670541). Phylogenetic analysis based on the concatenated sequences (ITS, Alt a 1, and LSU) revealed that the isolate YK1-24 clustered with A. gossypina strains. A pathogenicity test was conducted by spraying a conidial suspension (105 conidia/mL) onto the leaves of 5 pots of healthy 1-year-old O. hosiei seedlings. Five seedlings sprayed with distilled water served as the negative control. Plants were maintained in a greenhouse at 25°C with 85% humidity and 12 h photoperiod. By 20 days post-inoculation, all inoculated leaves exhibited symptoms consistent with those observed in the field, except controls. The pathogen was reisolated and confirmed as the inoculated fungus based on morphology. A. gossypina has been reported to cause leaf blight in tobacco and Castilleja tenuiflora (Guo et al. 2024; Solano-Báez et al. 2024). To our knowledge, this is the first report of A. gossypina causing O. hosiei leaf blight in China. These results support future phytosanitary monitoring and sustainable disease management strategies for this leaf blight.