Controle de Xanthomonas spp. com nanocristais de ZnO puros e dopados no tomateiro

Abstract

The tomato (Solanum lycopersicum L.) is the second vegetable of greatest economic importance in Brazil, but very affected by bacterial diseases. The bacterial leaf spot caused by Xanthomonas vesicatoria, X. euvesicatoria, X. gardneri and X. perforans leads to losses in the production and quality of tomato fruits, in addition to the chemical control of the disease being inefficient. However, new control alternatives have gained space, such as nanotechnology, where metallic nanocrystals have been used in agriculture, mainly in phytopathology, as a fungicidal and bactericidal agent. However, researchs involving the use of nanocrystals in the control of bacterial spot in tomato is scarce. Therefore, the objective of this work was: (i) evaluate the toxicity of pure and doped zinc oxide nanocrystals with different chemical elements in varying concentrations to inhibit bacterial growth in vitro; (ii) evaluate the exposure time of the nanocrystals to bacteria to cause mortality; (iii) evaluate the preventive and curative controls of the bacterial spot of tomatoes in a greenhouse using nanocrystals; (iv) evaluate the inoculation of the seeds with the bacterial suspension and the treatment of them with nanocrystals in the detection and germination of the seeds. Toxicity was evaluated based on the formation of a halo of inhibition of bacterial growth in vitro with pure and doped nanocrystals. For the evaluation of the bactericidal action in hours, the bacterial suspension (109 CFU/mL) was placed in contact with the solution of each nanocrystal and evaluated after plating after 0, 1, 2, 3, 4 and 5 hours of contact. For the preventive control of the bacterial stain, the plants were sprayed with nanocrystals and after 2 days they were inoculated with the bacterial suspension (108 CFU/mL). For curative control the plants were inoculated and 2 days later they were sprayed with nanocrystals. The severity of the disease was assessed using the diagrammatic scale and the area under the disease progress curve. Tomato seeds were inoculated with the bacterial suspension and treated with nanocrystals and the detection of the bacteria and germination of the seeds were evaluated. The pure ZnO nanocrystals showed, in general, greater capacity to inhibit growth, however doping with the elements Cu, Fe, Mg, Mn, Mo, Ni, Au, K and Ag also inhibited bacterial growth in vitro. The exposure time of the bacterial suspension to the nanocrystals solution for 5 hours was sufficient for mortality and decrease of CFU/mL, mainly with potassium doped nanocrystal. The preventive control reduced the disease severity in the plants and the ZnO nanocrystals doped with molybdenum were efficient for the control of the tomato bacterial spot. The seeds inoculated and treated with nanocrystals showed a lower percentage of detection of bacteria in the seeds, with ZnO K significantly reducing the presence of bacteria in the seeds and the germination of the seeds did not change with the use of nanocrystals.