Defense responses to mycotoxin-producing fungi Fusarium proliferatum, Fusarium subglutinans and Aspergillus flavus in kernels of susceptible and resistant maize genotypes.

Developing kernels of resistant and susceptible maize genotypes were inoculated with Fusarium proliferatum, Fusarium subglutinans and Aspergillus flavus. Selected defense systems were investigated using real-time RT-PCR to monitor the expression of pathogenesis-related (PR) genes (PR1, PR5, PRm3, PRm6) and genes protective from oxidative stress (peroxidase, catalase, superoxide dismutase and ascorbate peroxidase) at 72 hours post inoculation. The study was also extended to the analysis of ascorbate-glutathione cycle and catalase, superoxide dismutase and cytosolic and wall peroxidases enzymes. Furthermore, the hydrogen peroxide and malondialdehyde contents were studied to evaluate the oxidation level. Higher gene expression and enzymatic activities were observed in uninoculated kernels of resistant line, conferring a major readiness to the pathogen attack. Moreover expression values of PR genes remained higher in the resistant line after inoculation, demonstrating a potentiated response to the pathogen invasions. In contrast, reactive oxygen species-scavenging genes were strongly induced in the susceptible line only after pathogen inoculation, although their enzymatic activity resulted more consistent in the resistant line. Our data provide an important basis for further investigation of defense gene functions in developing kernels in order to improve resistance to fungal pathogens. Maize genotypes with over-expressed resistance traits could be profitably utilized in breeding programs focused on the resistance to pathogens and grain safety.