Metabolic response of downy mildew resistant and susceptible maize genotypes to Peronosclerospora sorghi

The metabolic response of downy mildew resistant (MAI 756) and susceptible (CM 500) maize (Zea mays L.) genotypes to Peronosclerospora sorghi (Weston & Uppal) Shaw, the causal fungus of maize downy mildew was assessed 0, 24, 48 and 72 h after inoculation by using gas chromatography coupled to electron impact ionization-time of flight-mass spectrometry (GC/EI-TOF-MS). A total of 95 metabolites were identified and annotated using the Golm Metabolome Database and Tag Finder software. Among them, 19 metabolites were up-regulated and unique to MAI 756, 4 up-regulated metabolites were unique to CM 500 and 72 metabolites were common to both the genotypes. Infection by P. sorghi substantially alters the plant metabolic profile, including significant changes in sugars, amino acids and phenylpropanoids. Up-regulation of DL-ornithine, cis-aconitic acid, citric acid, phthalic acid, cellobiose and xylopyranose were detected in the resistant maize genotype 24 h after inoculation, whereas N-acetyl-L-lysine, L-threonic acid, 1-cyclohexene-1-carboxylic acid and cinnamic acid have been detected 48 h after inoculation. The metabolites viz., erythro-pentonic acid and octadecenoic acid were up-regulated in the susceptible genotype 48 h after inoculation. This investigation provides new insight into the mechanisms of resistance in maize to P. sorghi at the metabolite level.