Bioactive Copper and Bacillus Subtilis for the Management of 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 the citrus orchard 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 and throughout the first year of establishment of the citrus orchard. The evaluations were carried out on eight mature branches per tree, determining the incidence of citrus canker, defoliation, and citrus leafminer (CLM) injures. The vegetative growth of the citrus trees, including tree height and trunk and canopy diameters, were also determined. In a experiment under controlled conditions to determine the activation of the systemic aquired resistance (SAR), the treatments were ASM and Bs applied via drench and, the BioCu and copper sulfate (SCu) were sprayed on the leaves. The expression of the PR-2 gene was evaluated by RT-qPCR at 24, 42, and 72 hours, and seven days after the application of the treatments. 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. 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 at 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