First Report of Bacterial Soft Rot on Blanched Chinese Chive ( Allium tuberosum Rottler ex Spreng.) Caused by Pantoea ananatis in China

Blanched Chinese chive (Allium tuberosum Rottler ex Spreng.) is cultivated under strictly controlled dark conditions, typically using opaque containers to suppress chlorophyll biosynthesis and inhibit photosynthetic activity. In March 2025, severe leaf soft rot was observed on blanched Chinese chive in Mile City (103.4° E, 24.45° N), Yunnan Province, China. Upon removal of the opaque containers, symptomatic leaves became desiccated and wilted within hours, accompanied by grayish-green to dark brown, water-soaked necrotic lesions. To identify the causal pathogen, 15 symptomatic plant samples were collected. Surface-sterilized tissue segments (5 × 5 mm) were plated onto nutrient agar (NA) and incubated in the dark at 30 °C for 72 h. All recovered isolates, including strains JH1–JH5, formed circular, smooth, yellow bacterial colonies. Preliminary identification based on 16S rRNA gene sequencing indicated that these isolates belonged to Pantoea ananatis, and strain JH1 was selected for subsequent molecular and phenotypic characterization. Species-specific PCR using primers PANA-1080F/R (Asselin et al. 2016) amplified a single target band from strain JH1, and the sequence was submitted to GenBank under accession PZ673042. Three housekeeping genes (gyrB, fusA, and leuS) were amplified and sequenced (Delétoile et al. 2009; Yamamoto et al. 1995), with sequences deposited under accessions PZ242891, PZ673041, and PZ673040. The consistent results from species-specific PCR and multilocus phylogenetic analysis strongly support the identification of strain JH1 as Pantoea ananatis, and this phylogenetic grouping is supported by a bootstrap value of 100%. Pathogenicity was assessed via in vivo inoculation tests. Strain JH1 was cultured until OD₆₀₀ reached 0.8. Fifty milliliters of bacterial suspension were sprayed onto healthy blanched Chinese chive, and 50 mL sterile distilled water served as the negative control. Each treatment included at least 30 plants with three independent biological replicates. Inoculated plants were incubated in darkness for 7 days. Soft rot symptoms indistinguishable from those observed in the field developed on inoculated plants, whereas control plants remained asymptomatic throughout the experiment. Bacteria were re-isolated from symptomatic tissues, and their identity was confirmed using primers PANA-1080F/R, fulfilling Koch's postulates. This is the first report of Pantoea ananatis causing soft rot on blanched Chinese chive in China. Previous work showed negligible virulence of Pantoea ananatis on green Chinese chive (Stice et al. 2018). Physiological changes during blanching, including reduced lignification and altered cuticular wax characteristics, may increase host susceptibility to bacterial infection. Collectively, these findings underscore the critical need for integrated disease management strategies specifically adapted to opaque container-based blanching cultivation systems.