Effects of copper and magnesium-based nanomaterials in management of bacterial spot of pepper

Bacterial spot of pepper (BSP) is an important disease caused by Xanthomonas spp. Copper-based bactericides have been widely used to manage this disease over the decades. This has resulted in the development of copper resistance in the pathogen. To this date, as a standard practice, mancozeb mixed with a copper material has been used instead of copper alone to control copper-tolerant strains of the BSP pathogen. As a result of the build-up of copper-tolerant strains, there is a need for an alternative to copper bactericides. Based on results of previous studies for control of bacterial spot-on tomato, we tested core-shell silica copper (CS-Cu), a copper-based nanomaterial as well as some magnesium-based nanomaterials like magnesium oxide (MgO), magnesium double coated copper (MgDC) and magnesium copper (MgCu) in vitro and in planta against X. euvesicatoria. In the in vitro experiments, all nanomaterials had bactericidal activity at concentrations as low as 200 ppm, ranging from 100-fold reduction to complete elimination of viable bacterial cells as compared to the commercial copper bactericide (Kocide 3000) and the control. In growth chamber experiments all the nanomaterials at 100 μg/ml or higher reduced disease severity ranging from 15 % to 56 % less disease compared to theuntreated control. In field experiments nanomaterials except MgO and MgCu at 100 μg/ml were able to reduce BSP severity ranging from 12 % to 50 % compared to untreated control, whereas their efficacy remained similar to that of Kocide-3000.