Identificação bioquímica, molecular e patogenicidade de isolados de Pseudomonas spp. provenientes de cafeeiros em Minas Gerais

Abstract

The bacterial diseases etiology comprise the main factors that affect a productivity of the coffee crop, among them, the coffee halo blight (Pseudomonas syringae pv. garcae - Psg), has gained significant importance in the recent years. In addition to this bacteriosis, the Brazilian coffee crops are also threatened by the coffee bacterial leaf spot, caused by P. syringae pv. tabaci - Psta, coffee bacterial blight, and coffee bacterial dark spot caused by P. cichorii - Pc and Burkholderia andropogonis - Ba, respectively. However, recent reports have been almost exclusively attributed to P. syringae pv. garcae. The diagnosis of these diseases has been mainly based on the visual symptoms and biochemical tests which have not been enough to correctly identify the pathogens in the species and pathovar levels. Therefore, more accurate methods for a reliable diagnosis of bacterial diseases of coffee are needed. Thus, the objectives of this work were to identify and differentiate the bacterial isolates from coffee crops of Minas Gerais state, by molecular techniques, phylogenetic analyzes, biochemical characterization and pathogenicity. These objectives will contribute to the clarification of the recent outbreak in the field of bacterial halo blight of coffee after more than 50 years later its detection. The biochemical characterization of the isolates, associated with PCR techniques, rep-PCR (REP, ERIC and BOX-PCR) and phylogenetic identification of rpoD locus, allowed to differentiate and identify 73 Psg, five Psta and six Pc strains, as well analyze the genetic diversity among them. The molecular techniques and biochemical tests reported in this study could be used in routine diagnosis of bacterial pathogens in coffee plants, since they discriminate the different pathogenic Pseudomonas species and pathovars that naturally occur in coffee crops. This is the first report of the occurrence of coffee bacterial leaf spot (Psta) under field conditions in Minas Gerais and the first report of coffee bacterial blight (Pc) outbreaks in nursery and field, since its first occurrence in Brazil. In the virulence tests, high pathogenic diversity was verified among Psg isolates tested. The reference isolate and eight Psg isolates considered to be the most virulent have caused disease in hosts of Psta Cucumis sativus, Carica papaya, Desmodium canum, Aster sp, Celosia plumosa and Phaseolus vulgaris. All the isolates reference of Psta, regardless of the host of origin caused disease in coffee seedlings.