Evaluation of Trichoderma harzianum to control downy mildew disease in sunflower under field conditions based on changes in the metabolite profiles of roots

Abstract

Two years of field testing were conducted in naturally Plasmopara halstedii-infested soils to assess the effectiveness of Trichoderma harzianum isolate (TRIC8) against downy mildew (P. halstedii) on sunflower (Helianthus annuus). Seed treatment with this antagonist offered protection of 73.64% in the first year. The effects of this treatment on oil content of the seeds and metabolite profiles of roots, along with disease severity, were evaluated in the second year by comparing to the fungicide treatment (Metalaxyl M). Oil content in seeds and metabolite profile in roots were studied using Nuclear Magnetic Resonance (NMR) and gas chromatography/mass spectrometry (GC/MS), respectively. TRIC8 and fungicide treatments were found to cause significantly lower disease severity when compared to that of the control, although weather conditions were more favorable for the disease in the second year than in the first year. The oil content in seeds with TRIC8 treatment was superior to that in seeds with fungicide treatment or control. The metabolites in roots from treated plants and disease severity were subjected to principal component analysis (PCA). TRIC8 treatment increased the accumulation of some alcohols [2-ethyl-2-methyltridecan-1-ol, 2-(propylamino)ethanol], aldehydes [2,5-bis(trimethylsilyloxy)benzaldehyde, dodecanal], alkanes (dotriacontane, eicosane, heneicosane, nonacosane, nonylcyclopropane, tetracontane, tetracosane), ketones [(1-hydroxycyclohexyl)-phenylmethanone, (4-methylphenyl)-phenylmethanone], an ester (6-ethyloctan-3-yl 6-bromohexanoate) and a terpene (falcarinol), which were among the metabolites that contributed over 0.70 in PC1 and were negatively correlated with disease severity. We suggest these metabolites might be involved in defense response of sunflower against P. halstedii in the field.