Rice bacterial blight is a devastating bacterial disease threatening rice yield all over the world and Xanthomonas oryzae pv. oryzae is traditionally believed to be the pathogen. In recent years, we have received diseased rice samples with symptoms of blighted leaves from Sichuan and Guangdong provinces, China. Pathogen isolation and classification identified two different enterobacteria as the causal agents, namely Enterobacter asburiae and Pantoea ananatis. Among them, E. asburiae was isolated from samples of both provinces, and P. ananatis was only isolated from the Sichuan samples. Different from rice foot rot pathogen Dickeya zeae EC1 and rice bacterial blight pathogen X. oryzae pv. oryzae PXO99A, strains SC1, RG1, and SC7 produced rare cell wall degrading enzymes (CWDEs) but more extrapolysaccharides (EPS). E. asburiae strains SC1 and RG1 produced bacteriostatic substances while P. ananatis strain SC7 produced none. Pathogenicity tests indicated that all of them infected monocotyledonous rice and banana seedlings, but not dicotyledonous potato, radish, or cabbage. Moreover, strain RG1 was most virulent, while strains SC1 and SC7 were similarly virulent on rice leaves, even though strain SC1 propagated significantly faster in rice leaf tissues than strain SC7. This study firstly discovered E. asburiae as a new pathogen of rice bacterial blight, and in some cases, P. ananatis could be a companion pathogen. Analysis on production of virulence factors suggested that both pathogens probably employ a different mechanism to infect hosts other than using cell wall degrading enzymes to break through host cell walls.
Keywords: Enterobacter asburiae; Pantoea ananatis; rice bacterial blight; virulence.