Resumo

Apple is one of the most important fruit crops consumed in the world. Its culture covers almost the whole region of the temperate climate in the Northern and Southern hemispheres. Currently, the conventional production system adopted for this culture depends on non-renewable resources, such as fertilizers, in addition to the excessive amount of insecticides. Several bacterial strains termed “plant growth promoting rhizobacteria” (PGPR) have been used to increase yield and quality of crops by various mechanisms, such as systemic resistance induction against various pathogens. This study aims to evaluate the diversity of cultivable PGPR isolated from rhizospheric soil and roots of apple trees cultivated under different crop systems in the south of Santa Catarina state. Samples of roots and rhizospheric soil of apple trees cultivated in: Native Field (NF), Orchard Organic (OO), and Orchard Conventional (OC) were collected, together with soil samples from an area never used for agriculture. Bacteria were identified at the genus level by PCR-RFLP 16S rRNA gene analysis and partial sequencing and were evaluated for their ability to produce indolic compounds, siderophores and to solubilize phosphates. The antagonistic ability of these bacteria against Colletotrichum gloeosporioides, the causal agent of leaf spot disease, was also evaluated. Among the 300 strains isolated, 214 were able to produce siderophores, 34 were able to solubilize phosphates and 21 isolates produced more than 100 mg ml-1 of indolic compounds in in vitro assays. A seventy six isolates presented some antagonist activity against C. gloeosporioides, probably due to antibiotic production. Among the most abundant genera identified were, respectively, Rahnella sp., Enterobacter sp., Pseudomonas sp., Stenotrophomonas sp., Rhizobium sp., Pantoea sp., and Raoultella sp. An in vivo experiment was conducted in a greenhouse and isolate 89 (identified as Microbacterium schleiferi) was able to reduce the damage of the phytopathogenic fungus. Seven days after fungus exposition plants inoculated with isolate 89 presented, on average, only 30% of their leaf area affected, whereas plants without bacterial treatment presented between 60 to 73% of their leaf area affected by fungus attack. This result is very promising for agronomical purposes since it will give to producer’s time to prevent further fungal damages.