Doped zinc-oxide nanocrystals for the control of tomato bacterial spot and Xanthomonas gardneri in seeds

Bacterial spot caused by Xanthomonas spp. may result in significant losses to tomato crops. The use of metallic nanocrystals offers a novel approach for disease control. The objective of this work was to evaluate doped zinc-oxide (ZnO) nanocrystals in the control of bacterial spot (Xanthomonas gardneri) and in tomato seed treatment. The toxicity of the doped ZnO nanocrystals was evaluated by determining the in vitro bacterial growth inhibition zone. To assess the preventive application, tomato plants were sprayed with ZnO:1K, ZnO:1Mg, or ZnO:0.5Mo nanocrystals, copper, and water, and after 2 days, the plants were inoculated with a bacterial suspension (108 CFU/mL). To assess the curative application, the plants were inoculated with the bacteria, and 2 days later sprayed with the products. Disease severity was evaluated, and the area under the disease progress curve was calculated. Tomato seeds were inoculated with the bacteria and treated with the nanocrystals, and the percentages of bacteria detected and seeds germinated were determined. The doped ZnO nanocrystals inhibited bacterial growth. The 5-h exposure time to ZnO:1K nanocrystals was sufficient to reduce bacterial growth from 108 CFU/mL to 1.42 × 102 CFU/mL. ZnO:0.5Mo, ZnO:1K, or ZnO:1Mg nanocrystals reduced disease severity in the preventive application, reduced the presence of bacteria in the inoculated seeds, and did not affect seed germination. The use of nanocrystals showed promising to manage bacterial spot and to treat tomato seeds.