Volatile compounds released by maize grains and silks in response to infection by Fusarium verticillioides and its association with pathogen resistance

Many plants respond to fungal infections by producing and/or emitting a specific blend of oxylipins, some of them through the lipoxygenase (LOX) pathway. In vitro bioassays revealed that volatiles from silks and grains of a set of six maize genotypes with variable resistance to Fusarium verticillioides affected fungal growth in different ways. Analyses by solid phase microextraction and GC-MS showed different volatile profiles in silks and grains of each genotype. Susceptible genotypes with higher concentrations of precursor polyunsaturated fatty acids produced more volatiles, mainly C9 compounds, in comparison to moderately resistant ones. Real-time PCR from several lipoxygenase transcripts revealed that levels of gene expression depended on the genotype and the inoculation level and suggested that F. verticillioides could use compounds from the 9-LOX pathway to promote infection in grains. On the other hand, volatiles produced by the 13-LOX pathway were more important in moderately resistant genotypes and could be associated to field resistance. Results from this set of genotypes indicate that LOX-regulated volatile compounds might be important in F. verticillioides infection and should be targeted in further research to understand disease resistance.