Occurrence of Stagonosporopsis caricae Causing Blueberry Blossom Blight in Yunnan Province of China

Abstract

Blueberries (Vaccinium spp.), economically important fruit crops with rich nutritional properties, have been extensively cultivated in China in recent years (Zhou et al. 2025). In November 2023 to March 2024, blossom blight was observed on blueberries in plastic tunnels in Honghe Hani and Yi Autonomous Prefecture (23.68° N, 102.77° E), Yunnan, China. The disease incidence ranged from 8% to 14%. Infected blueberry petals showed necrotic lesions and covered with a brownish mold layer under high humidity. Some blossoms shriveled and remained adherent to the fruit, with stunted fruit development. Symptomatic blossom blight samples were excised from lesion margins, surface-sterilized with 75% ethanol for 45 seconds, rinsed three times with sterile distilled water, then placed onto 25% lactic acid-supplemented potato dextrose agar (PDA). After incubating at 25°C for 3 days, hyphal tips from the colony margins growing out of diseased tissues were transferred onto fresh PDA. Seven morphologically similar isolates were obtained. The colonies were subcircular with abundant aerial mycelia at 25°C, being dark gray on PDA and light gray on oatmeal agar (OA) at 7 days post inoculation (dpi). Isolate JSLMG6-1 was randomly selected for identification and pathogenicity assay, with mycelial growth rates of 9.6 and 5.3 mm/d on PDA and OA at 25°C, respectively. For sporulation, it was incubated on V8 agar at 25°C in darkness for 5 days, followed by continuous UV irradiation at 25°C for another 9 days. Pycnidial conidiomata were globose to subglobose, 71.1-124.6 μm in diameter, ostiolate, with walls of pale brown to dark brown textural angularis. Conidia were short cylindrical or slightly reniform, straight to slightly curved, nonseptate, hyaline, mearing 7.3-17.2 × 2.6-5.0 μm (mean 10.3 × 3.7 μm). The morphological characteristics were similar to those of Stagonosporopsis caricae (Aveskamp et al. 2010; Bracale et al. 2020; Zhang et al. 2023). DNA fragments of internal transcribed spacer (ITS), calmodulin (CAL), chitin synthase I (CHS), and β-tubulin (BTUB) were amplified and bidirectionally sequenced (Han et al. 2026). The sequences were deposited in GenBank (accession nos. PX904963, PX905966-PX905968). Bayesian inference phylogeny based on concatenated ITS, CAL, CHS, and BTUB sequences showed that the isolate JSLMG6-1 clustered together with four previously reported strains of S. caricae, including CBS 102399, CBS 248.90, PS1-1, and RV16 (Stewart et al. 2015), and formed an independent clade supported by a posterior probability value of 1. Thus, the isolates from blueberry blossom blight samples were identified as S. caricae. Pathogenicity tests were conducted on unwounded blueberry blossoms, fruits, and leaves of tissue-cultured plantlets using 5-mm mycelial plugs of JSLMG6-1 (controls: PDA plugs). Inoculated materials were incubated at 25°C under a 14/10 h photoperiod with >80% relative humidity. Six replicates per treatment, the experiment was repeated twice. Necrotic lesions developed at all inoculated sites on blossoms (4 dpi), fruits (10 dpi), and leaves (10 dpi), while PDA controls remained healthy. S. caricae was re-isolated from diseased tissues and confirmed by morphological and molecular identification. To our knowledge, this is the first report of S. caricae causing blueberry blossom blight in China. S. caricae could also be a potential pathogen of blueberry fruit rot and leaf spot. This study is crucial for the diagnosis and management of blueberry diseases.