Abstract
Bacterial spot, caused by Xanthomonas spp., is a highly destructive disease of tomatoes worldwide. Copper (Cu) bactericides are often ineffective due to the presence of Cu-tolerant strains. Magnesium oxide (MgO) is an effective alternative to Cu bactericides against Xanthomonas spp. However, the effects of particle size on bactericidal activity and fruit elemental levels are unknown. In this study, nano (20 nm) and micron (0.3 and 0.6 µm) size MgO particles were compared for efficacy. Nano MgO had significantly greater in vitro bactericidal activity against Cu-tolerant X. perforans than micron MgO at 25–50 µg/ml. In field experiments nano and micron MgO applied at 200 and 1,000 µg/ml were evaluated for disease control. Nano MgO at 200 µg/ml was the only treatment that consistently reduced disease severity compared to the untreated control. Inductively Coupled Plasma Optical Emission Spectroscopy revealed that nano MgO applications did not significantly alter Mg, Cu, Ca, K, Mn, P and S accumulation compared to fruits from the untreated plots. We demonstrated that although both nano MgO and micron MgO had bactericidal activity against Cu-tolerant strains in vitro, only nano MgO was effective in bacterial spot disease management under field conditions.
Highlights
Bacterial spot, caused by Xanthomonas spp., is a highly destructive disease of tomatoes worldwide
Bactericidal activity of different particle size of Magnesium oxide (MgO) compared with Cu bactericide
The Cu bactericide (Kocide 3000) (Fig. 1C) had 80.7% alive cells, which was similar to the untreated control (80% alive cells) (Fig. 1A)
Summary
Bacterial spot, caused by Xanthomonas spp., is a highly destructive disease of tomatoes worldwide. Magnesium oxide (MgO) is an effective alternative to Cu bactericides against Xanthomonas spp. We demonstrated that both nano MgO and micron MgO had bactericidal activity against Cu-tolerant strains in vitro, only nano MgO was effective in bacterial spot disease management under field conditions. Given that Florida’s tomato production industry has a long history with bacterial spot disease, the pathogen has developed resistance toward bactericides including streptomycin[7,8] and copper (Cu)[2,9]. Other available alternatives to Cu include plant defense activators such as acibenzolar S-methyl[15], and plant-growth-promoting rhizobacteria that provide limited disease control under field conditions[19]. Nanoparticles including magnesium oxide (MgO), have been recently shown to have potential to be an alternative to Cu-EBDC20–23
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