Bioactive copper and Bacillus subtilis for the control and resistance induction against citrus canker in sweet orange [Citrus sinensis (L.) Osbeck] orchard establishment

Resistance is the plant ability to prevent or delay the infection and the development of a pathogen. The objective of this study was to determine the efficiency of treatments with chemical and biological products for the control of citrus canker during the establishment of citrus orchards through resistance induction. The treatments consisted of a combination of foliar and drench applications of products based on Bacillus subtilis (Bs), bioactive copper (BioCu), copper hydroxide (HCu) and acibenzolar-S-methyl (ASM), at the transplanting of the nursery trees to the field and throughout the first year of establishment of the citrus orchard. Evaluations were carried out on mature branches determining the incidence of citrus canker, defoliation, and citrus leafminer (CLM) injures. The vegetative growth of the citrus trees, i.e. tree height and trunk and canopy diameters, were also determined. Under controlled conditions, studies were carried out to determine the activation of the systemic acquired resistance (SAR) by treatments with ASM and Bs applied via drench, and by BioCu and copper sulfate (SCu) applied by spraying on the leaves of the citrus trees. The expression of the PR-2 gene was evaluated by RT-qPCR at 24, 42, and 72 h, and seven days after the application of the treatments. In the field, the ‘IAPAR 73′ sweet orange trees treated via drench with Bs and foliar applications of Bs + HCu, Bs + BioCu and HCu with and without ASM showed reductions in the incidence of citrus canker. HCu treatments reduced defoliation, while foliar treatments with Bs decreased the incidence of CLM injures. The ‘IAPAR 73′ sweet orange trees treated with ASM showed a reduction in the vegetative growth. The BioCu and Bs products were effective for the control of citrus canker in young citrus trees during the orchard establishment. In addition, the BioCu product increased the expression of the PR-2 gene, which encodes the β-1,3 glucanase, a protein associated with the systemic acquired resistance (SAR) in plants.