First Report of Pantoea agglomerans Causing Leaf Blight on Wheat in Gansu Province, China

Bacterial leaf blight is rising to an important challenge in Wheat (Triticum aestivum) production, causing the leaf spots, yellowing, wilting and even death during the seedling stage in recent years. During 2024 to 2026, a new devastating disease exhibiting leaf blight like symptoms was observed in the wheat fields in Wuwei City of Gansu Province, China. The typical symptoms of the disease in the field are bright yellow leaf spots and patches with chlorosis that spread along the veins in the early stage, causing the entire wheat leaf to turn yellow and wither, and eventually develop into the necrosis and blight of the plant. The cultivar Yongliang 15 exhibiting these symptoms was distributed over approximately 10 ha of the major wheat area, with an average disease incidence between 15 and 25%. The tissues of boundary between diseased and healthy parts from the typical leaves were collected and disinfected in 5% NaOCl solution for 3 min, rinsed 3 times in sterile distilled water, crushed aseptically in 1 ml sterilized water and immersed for 10 min. The suspension was evenly spread on the surface of the nutrient agar (NA) plate for culture and further purification (Xu et al. 2026). After 48 hours, predominant colonies which appeared pale yellow, round, raised, smooth and mucus-like were consistently detected, and no fungi or other dominant bacteria were observed. Pure cultures with uniform morphology were short rod-shaped, gram-negative with peritrichous flagella. To determine the species of the bacteria, partial sequences of the universal 16S rRNA gene and gyrB gene were respectively amplified using the primer pair 27F/1492R (Marchesi et al. 1998) and the primer pair 1S/2rS (Brady et al. 2008), and sequenced by Tsingke Bio-technology (Xian, China). The 16S rRNA sequence (PV701179, 1388 bp) and gyrB sequence (PX251124, 1142 bp) were submitted to GenBank and compared with reported nucleotide sequences using BLAST search to determine homology in the NCBI database. The 16S rRNA sequence had remarkable 99.86 to 99.93% identity with the Pantoea agglomerans from olive tree in Morocco (OK605842), onion in USA (OR831876), and cotton boll in China (EU598802). The gyrB sequence exhibited 99.56 to 99.82% identity with that of P. agglomerans from kidney beans in France (CP143414), wheat in China (ON461801), and soil in UAE (CP048033). The results showed the bacteria clustered with the P. agglomerans clade through phylogenetic analysis, with the neighbor-joining method of MEGA11. Eight 25-day-old healthy seedlings (Yongliang 15) were inoculated with 60 μl of the bacterial suspension (108 CFU/mL) through a sterile syringe needle poked into the main leaf veins for the pathogenicity test to complete Koch’s postulates. Control seedlings were inoculated with sterile distilled water in the main leaf veins, and all seedlings were kept in a greenhouse (28±2℃, >60% RH). At 3 days, symptoms appeared in inoculated seedlings, and after 6 days, all the inoculated leaves of wheat exhibited chlorotic and yellow spots around the poked veins like the symptoms observed early in the field, whereas the control leaves grew normally. Bacteria were isolated from inoculated leaves tissues and identified as P. agglomerans using the molecular analysis of 16S rRNA and gyrB described above. P. agglomerans has been reported to cause leaf blight of wheat in Ningxia Hui Autonomous Region of China (Gao et al. 2023) and Colorado of USA (Diego et al. 2024). To our knowledge, this is the first report of P. agglomerans naturally causing leaf blight on wheat in Gansu Province, China. Early identification of the disease will help control the damage and reduce losses.