PATOGENICIDADE E BIOCONTROLE DE Sclerotinia sclerotiorum (Lib.) DE BARY EM SEMENTES DE Eucalyptus benthamii MAIDEN ET CAMBAGE

Abstract

In Brazil, the occurrence of Sclerotinia sclerotiorum is verified in agricultural crops of high economic value and its damages can lead to losses close to 100% in some hosts. In the eucalyptus crop, S. sclerotiorum is reported as a potential pathogen, but studies of the natural occurrence of this fungus and its effects on the crop are not yet described. It is believed that, with the expansion of the agricultural frontier in Brazil, fungi that had not previously occurred in a particular crop, may be migrating to new areas, adapting and colonizing new hosts. Thus, studies on the pathogen, the relationship with crop, damages and control measures are required. In agriculture the control used for S. sclerotiorum is the chemical, however with dubious efficacy. The high costs and the accumulation of chemical residues in the environment have made biological control an alternative method in the control of this phytopathogen. Thus, the present study aimed to evaluate the effects of S. sclerotiorum on Eucalyptus benthamii seeds and to select in assays in vitro and in vivo rhizobacteria and resident bacteria of the phylloplane with potential for the biocontrol of this phytopathogen. The seed health, germination and emergence of E. benthamii seeds, inoculated with a S. sclerotiorum isolate, were evaluated. The antagonistic capacity of 269 bacteria was evaluated by means of three in vitro assays. The isolates that showed potential in the tests performed were selected for two in vivo control assays. The fungus was considered to be pathogenic to E. benthamii seeds when inoculated by the substrate method. The symptoms observed in the seeds were pre and post-emergence damping-off. Only four bacterial isolates were able to control the pathogen in vitro. It was verified the difficulty to select in vivo isolates with antagonistic potential due to the variable effect presented by the isolates. In the first control assay, it was not possible to observe a beneficial effect of the bacterial isolates. In the second assay, the isolates identified as Bacillus sp. and Bacillus pumilus showed beneficial effect to the seeds for most of the evaluated parameters and showed to be colonizers of the root system. The pathogenicity of Sclerotinia sclerotiorum to E. benthamii seeds is concluded and the isolates Bacillus sp. and Bacillus pumilus have potential for the biocontrol of this phytopathogen.