Pseudomonas coronafaciens pv. garcae and P. amygdali pv. tabaci isolated from coffee plants cause diseases in different species

ABSTRACT Bacterial halo blight and bacterial leaf spot have similar symptoms in coffee plants, and the etiological agents Pseudomonas coronafaciens pv. garcae (Pcg) and P. amygdali pv. tabaci (Pat) have very similar colony morphologies and biochemical characterizations, which makes it difficult to provide a correct diagnosis. To date, Coffea arabica is the only known natural host of Pcg, while Pat affects a wide range of host plants. However, no studies have yet been conducted to test the pathogenicity of Pcg strains in Pat hosts or Pat strains from different hosts in coffee plants. The objectives of this study were to evaluate the virulence level among Pcg strains and to perform cross-inoculation tests to confirm the hosts specificity for Pcg and Pat. In the virulence tests, there was variation in aggressiveness among Pcg strains. The reference isolate (CFBP 1634) and seven Pcg strains considered more aggressive were selected for cross-inoculation testing on different Pat hosts. All the Pat strains, regardless of the host of origin, caused disease in the coffee seedlings and Pcg strains caused disease in Phaseolus vulgaris, Cucumis sativus, Carica papaya, Aster sp., Coffea arabica, Celosia plumosa and Desmodium incanum. Therefore, there is no host specificity for Pcg and Pat, using artificial inoculation. These results are important for the beginning of the knowledge of the host range of Pcg and may contribute to the development of strategies to manage the disease.