Mildew-Induced Resistance in Roses Against Spodoptera exigua and Chemical Compounds Produced During the Defense Response.

In the ternary system of Podosphaera pannosa, Spodoptera exigua, and Rosa chinensis, volatiles from infected roses suppress S. exigua oviposition, but the non-volatile-mediated resistance mechanism remains unclear. This study investigated mildew-induced resistance in roses by assessing larval feeding responses to leaf extracts. Infected rose leaf extracts significantly inhibited larval feeding (68.55% inhibition; t = 4.742, df = 28, p = 0.0002). Untargeted LC-MS metabolomics identified 1046 metabolites in R. chinensis. P. pannosa infection altered the rose metabolome, yielding 64 differentially accumulated metabolites (47 up, 17 down). Among these, five compounds were markedly upregulated: dehydro(11,12) ursolic acid lactone (A), maslinic acid (B), trametenolic acid B (C), betulonic acid (D), and ganolucidic acid B (E). All five inhibited larval feeding. Compound A showed the strongest activity (80.99% at 0.1 mg/mL), with an EC50 of 0.015 mg/mL. EC50 values for compounds B-E were 1.256, 0.067, 1.189, and 0.014 mg/mL, respectively. This study elucidates a resistance mechanism of mildew-induced roses and suggests that compounds with low EC50 values (e.g., A and E) warrant further investigation as potential candidates for eco-friendly pest management under laboratory conditions.