First report of bacterial dieback of rice caused by <i>Pantoea anthophila</i> in Guangxi, China

Rice is a major staple crop in China and worldwide, and bacterial diseases threaten its production (Doni et al. 2021; Lv et al. 2022). In 2025, typical leaf tip dieback symptoms were observed on rice seedlings in a rice field planted with cv. Fuxiangnian in Binyang County (23.25834°N, 108.92461°E), Guangxi, China. Symptoms initially appeared as reddish-brown blighted lesions at the leaf tips, gradually extending downward and eventually leading to complete leaf dieback. In severe cases, lesions coalesced and formed irregular necrotic areas. Approximately 667 ha were affected, and disease incidence was estimated at 90 ± 5% in the surveyed fields. Leaf samples showing typical symptoms were collected from five locations for bacterial isolation. Leaf pieces (5 × 5 mm) excised from the margins of symptomatic tissues were surface-disinfested with 75% ethanol, macerated under sterile conditions, and streaked onto King’s B (KB) medium. After incubation at 28°C for 2 days, 20 colonies with similar morphologies were obtained. Colonies were circular, mucoid, raised, translucent, smooth, yellow-pigmented, and had entire margins. One representative isolate, designated Pa1, was selected for further characterization and pathogenicity testing. Strain Pa1 was transferred to sterile KB broth and incubated at 28°C with shaking at 220 rpm for 15 h to obtain a bacterial suspension. The nearly full-length 16S rRNA gene of strain Pa1 was amplified using the universal primers 27F and 1492R. The resulting 1,444-bp amplicon (GenBank accession no. PZ279562.1) shared 99.71% sequence identity with Pantoea anthophila strain LMG 2558. Whole-genome sequencing of Pa1 (GenBank accession no. JBXGEE000000000.1) revealed 98.75% average nucleotide identity (ANI) and 90.70% digital DNA-DNA hybridization (dDDH) with P. anthophila strain LMG 2558 (Zhang et al. 2023). Phylogenetic analysis based on the concatenated sequences of 31 housekeeping genes further showed that strain Pa1 clustered with P. anthophila strain LMG 2558, supporting its taxonomic placement as P. anthophila. In addition, Biolog analysis further supported the assignment of strain Pa1 to the genus Pantoea. To determine the pathogenicity of strain Pa1 on rice, seedlings of rice cultivar Fuxiangnian were inoculated using the leaf-clipping method. Bacterial cells from a 24-h culture grown on KB medium were suspended in 10 mM MgCl2 and adjusted to 1 × 106 CFU/mL. Nine healthy plants were inoculated with the bacterial suspension, nine additional plants treated with sterile 10 mM MgCl2 served as negative controls. All plants were maintained in a greenhouse at 28°C and 85% relative humidity. The experiment was repeated three times with similar results. Seven days after inoculation, reddish-brown lesions developed only on inoculated leaves and were similar to those observed in the field, whereas no symptoms developed on the control plants. Bacteria reisolated from symptomatic leaves were morphologically identical to strain Pa1, and the 16S rRNA sequence of the reisolated strain was identical to that of Pa1, thereby fulfilling Koch’s postulates. To our knowledge, this is the first report of P. anthophila causing bacterial dieback of rice in Guangxi, China. This finding highlights the need for effective phytosanitary measures to prevent the introduction and spread of this pathogen to other rice-growing areas.