Nitrate availability influences powdery mildew resistance and secondary metabolism in Gerbera hybrida.

Powdery mildew (Podosphaera xanthii) is a major disease affecting gerbera (Gerbera hybrida, Asteraceae), and nitrogen availability is a key factor influencing disease development. Our objective was to determine how nitrate availability affects resistance to Podosphaera xanthii through changes in primary and secondary metabolism. Using greenhouse experiments and 1H nuclear magnetic resonance-based metabolomics, we found that lower nitrate levels reduced infection, supporting the concept of nitrogen-induced susceptibility. Reduced nitrate availability was associated with decreased amino acid levels and increased accumulation of defense-associated metabolites such as polyketide and phenylpropanoid metabolites, including gerberin, gerberinside, parasorboside, and chlorogenic acid derivatives. Notably, moderate nitrate reduction enhanced resistance without compromising flower biomass, provided that nitrate supply remained above 3 mM. Our results highlight nitrate management as a potential strategy for sustainable disease control.