First report of <i>Pantoea alfalfae</i> causing leaf blight on maize ( <i>Zea mays</i> ) in Xinjiang Province, China

Leaf blight symptoms were observed on maize (Zea mays L.) during a field survey in Xinjiang Province, China in July 2025, some plants in several plots were exhibiting long, water-soaked lesions with a pale-yellow halo, and the affected area was estimated to be approximately 1 km2 Small pieces (approximately 3 mm) from symptomatic leaves, cut from the leading edges and briefly surface-sterilized in 75% ethanol, were thoroughly washed and transferred to Luria Bertani (LB) agar. After incubation at 28°C, yellow smooth colonies, relatively consistent on different LB plates, appeared after 48 hours and the strain was named as 4D. Next, detached-leaf inoculations and whole-plant tests (greenhouse assay) were performed with a suspension of 4D at 1 × 108 CFU/mL. Leaves were gently wounded with needles, and the suspension was sprayed onto the leaf surface (sprayed to near runoff). Whole-plant inoculation was used as the primary pathogenicity assay. Lesions resembling those observed in the field developed on inoculated maize leaves 5 days after spray inoculation, whereas control plants remained symptomless. However, the pattern developed somewhat differently under greenhouse conditions, probably due to differences in humidity and leaf age compared with the field conditions. The bacterium was re-isolated from the artificially infected leaves through dilution plating, and its colony characteristics matched those of the original isolate, fulfilling Koch's postulates. In addition, genomic DNA extracted using cetyl-trimethyl ammonium bromide (CTAB) protocol (Doyle and Doyle 1987) was used to amplify three commonly used genes: 16S rRNA, rpoB, and gyrB with standard primer pairs (27F/1492R, rpoBCM81-F/rpoBCM32b-R, and UP-1/UP-2r). (Galkiewicz and Kellogg 2008; Brady et al. 2008; Yamamoto and Harayama 1995). The whole-genome assembly of isolate 4D was deposited in GenBank under accession no. CP082292, and the 16S rRNA, rpoB, and gyrB sequences were deposited under accession nos. PX533078, PX570105, and PX570106, respectively. All three sequences shared 99.6-99.8% identity with Pantoea alfalfae CQ10, a strain previously linked to alfalfa (Yao et al. 2023; Yu et al. 2022). Further, phylogenetic inference based on a concatenated multilocus alignment grouped isolate 4D with the CQ10 type strain, with full bootstrap support, clearly separating it from other closely related Pantoea species, such as P. ananatis or P. agglomerans (Brady et al. 2008; Shin et al. 2022). Importantly, to determine the pathogen host range, we also inoculated healthy alfalfa seedlings, which developed clear chlorosis and wilting after about one week, while LB and water controls remained unaffected. Re-isolated strains validated previous findings. Taken together, field observations, pathogenicity results, and multilocus sequence data suggest that P. alfalfae is the causal agent of maize leaf blight observed in Xinjiang, China. This is the first report of Pantoea alfalfae causing leaf blight on maize in China. The finding expands the known host range of the pathogen and indicates a potential cross-host risk in maize–alfalfa rotation systems.