Detecção de Pantoea ananatis em sementes de milho e nanopartículas no controle da bactéria in vitro

Abstract

The white corn stain caused by the bacterium Pantoea ananatis is considered one of the main foliar diseases of maize in Brazil. The control strategies of the disease are based on obtaining resistant genotypes and chemical control. As a new strategy, several nanomaterials have been used as antimicrobial agents to eliminate or retard bacterial growth. The objective of this study was to (i)evaluate semi-selective culture medium for the detection of P. ananatis; (ii) to detect the presence of P. ananatis in seeds of eight maize genotypes; (iii) to identify and characterize biochemistry and molecularly the bacterial isolates; (iv) to evaluate the effect of nanoparticles in the control of the bacterium in vitro. To evaluate the culture media, two isolates of P. ananatis were used in five culture mediums (523, NA, TSA, PA10 and PA20) with absence or presence of the fungicides cyclohexamide and methyl thiophanate, with three replicates each. The efficiency of each culture medium was determined from the diameter of the colonies and counting of the number of colonies in CFU mL-1. Eight maize genotypes were used to detect the bacteria in the seeds, the seed extracts were grown in three culture media (523, NA and TSA) with three replicates for each dilution. The obtained isolates were characterized biochemically, physiologically and molecularly. In order to control with nanoparticles, ZnO nanocrystals doped with six elements: silver (Ag), gold (Au), copper (Cu), iron (Fe), manganese (Mn) and nickel (Ni) in different concentrations and pure nanocrystals, with three replicates. The direct toxicity of the nanocrystals was evaluated through the halo of bacterial growth inhibition (Pantoea ananatis isolate) in culture medium. TSA and 523 culture media with addition of cyclohexamide were effective for the detection of P. ananatis. The bacterium was detected in seeds of five maize genotypes. TSA culture medium with addition of cyclohexamide may be recommended for the detection of P. ananatis in corn seeds. The use of zinc oxide (ZnO) nanoparticles did not present a bactericidal effect for P. ananatis. ZnO nanocrystals doped with copper, iron, manganese, nickel, gold and silver inhibited the growth of P. ananatis in vitro.