Identification, pathogenicity, and virulence of the causal agent of bacterial scab disease on mango in China

Mango is an important economic fruit in China. As the mango cultivation areas continue to expand, symptoms of bacterial scab disease have been observed on mango fruits from orchards in Hainan Province, China. Through a combination of morphological diagnoses, pathogenicity tests, physiological and biochemical characterizations, and phylogenetic analysis, the causal pathogens were identified as three distinct bacterial species: Enterobacter hormaechei, Pantoea dispersa, and Pseudomonas oryzihabitans. When compared to Xanthomonas citri pv. mangiferaeindicae XC01, the causal agent of bacterial black spot in mangoes, E. hormaechei produced more cell wall degrading enzymes (CWDEs), while P. disperse produced more cellulases but fewer proteases. Moreover, these two strains released higher amounts of extracellular polysaccharides (EPS). In contrast, P. orzihabitans could not produce cellulases or proteases, except for amylases. Additionally, we evaluated the motility capabilities of the three strains, including swimming and swarming motility. All strains showed lower swimming abilities than XC01. Specifically, E. hormaechei and P. disperse swam more slowly than XC01, and only P. disperse exhibited faster swarming behavior compared to XC01. Among the twelve tested chemical agents, albendazole showed the highest inhibition rates against E. hormaechei and P. disperse, with EC50 values (the concentration required for 50% maximal effect) recorded at 0.0002 mg/L and 0 0.0001 mg/L, respectively. This study is the first to identify E. hormaechei, P. dispersa, and P. oryzihabitans as new pathogens of mango bacterial scab disease. These findings lay a foundation for future field control strategies against mango bacterial scab.