First Report of Rhizome Rot on Ginger Caused by <i>Serratia marcescens</i> in Qinhuangdao, China

Ginger (Zingiber officinale Rosc.) is an important horticultural crop in China, especially the rhizome tissue, which has a high medicinal value. In October 2024, symptoms of soft rot appeared on ginger during harvest in Qinhuangdao City of Hebei Province, with an incidence of 5% (39°41′N, 119°04′E).The pathogen infected rhizomes and leaves, resulting in leaf chlorosis, progressive wilting culminating in collapse of entire plants, and rhizome softening accompanied by dark brown maceration. From three diseased tissue samples, fourteen isolates were obtained by tissue isolation and NA medium purification, and one isolate was selected for further analysis. The colonies were red, circular, smooth, and convex on NA. The isolate was gram-negative, facultatively anaerobic, and negative for the methyl red (MR) test and hydrogen sulfide (H2S) production, as well as positive for gelatin hydrolysis and the Voges-Proskauer (V-P) test. It utilized glucose, sucrose, xylitol, maltose, and sorbitol. To further confirm the identification, the partial 16S rRNA and trpB genes were amplified and sequenced using primers 27F/1492R (Lane 1991) and trpb-F/trpb-R (Rong 2009). The isolate's 16S rRNA (PV422728) and trpB (PV477047) sequences shared 99.79% and 98.06% identity, respectively, with those of Serratia marcescens (MN519524.1 and CP013046.1, respectively) in GenBank. The pathogenicity of the isolates was tested on ginger plants and rhizome tissue. Twelve healthy ginger seedlings were inoculated by injecting 0.3 mL of bacterial suspension (10⁸ CFU/mL) into both basal stems and rhizome centers. Controls received an equal volume of sterile water. The inoculated plants were kept in a growth chamber (28°C, 16-h light and 8-h dark period), and ginger rhizomes were placed in an incubator (30°C, 24-h dark period). At 16-20 days post-inoculation, severe chlorosis and wilting developed in the stems and leaves. Water-soaked, brown, and rotted rhizome tissue developed about 5 d after inoculation on rhizomes. No obvious symptoms were observed on the control plantlets and rhizome tissue. Bacterial colonies reisolated from infected rhizomes were identified as S. marcescens through consistent morphological, biochemical, and molecular analyses, fulfilling Koch's postulates. To date, the ginger rhizome rot pathogen S. marcescens has been identified in Chongqing, China (Huang et al. 2020). To our knowledge, this is the first report of S. marcescens as the pathogen causing ginger rhizome rot in Qinhuangdao, Hebei, China. The identification of this pathogen will enable targeted field management to control this disease.