Phenolics in maize genotypes differing in susceptibility to Gibberella stalk rot (Fusarium graminearum Schwabe)

The relationship between phenolic compounds and maize pith resistance to Fusarium graminearum, the causal agent of Gibberella stalk rot, was investigated. The phenolic acid profiles in the stalks of six maize inbred lines of varying susceptibility were evaluated from silking to grain maturity. Four different fractions of phenolic compounds were extracted from inoculated and non-inoculated (control) pith tissues: insoluble cell-wall-bound, free, soluble ester-bound, and soluble glycoside-bound phenolics. Analysis by HPLC revealed that p-coumaric acid and ferulic acid were the most abundant compounds in the soluble and cell-wall-bound fractions. The quantity of free, glycoside-bound, and ester-bound phenolics in the pith was lower than the level required for the inhibition of Fusarium growth or mycotoxins production; however, significant negative correlations between diferulic acid contents in the cell walls and disease severity ratings 4 days after inoculation were found. The results indicated that future studies should focus on the levels of diferulic acids during the early infection process. Diferulates may play a role in genotypic resistance of maize to Gibberella stalk rot as preformed barriers to infection.