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This study investigated changes in volatile organic chemicals (VOCs) of rose plants (Rosa chinensis Jacq.) after treatment with tenuazonic acid (TeA). TeA is a toxin produced by Alternaria alternata (Fr.) Keissler and is a key virulence factor for infection of the plants by the fungus. VOCs were collected in situ separately from intact live twigs of healthy and TeA-treated rose plants by dynamic headspace adsorption (DHSA) or from cut twigs of healthy and treated roses by headspace solid-phase microextraction (HS-SPME) and identified by gas chromatography–mass spectrum (GC–MS). VOC emissions changed significantly after the plants were treated with TeA based on the results obtained with both methods. GC–MS and chemometrical analysis show that the content of monoterpenes significantly increased the most, followed by ketones and alcohols, whereas sesquiterpenes decreased significantly, resulting from the induction by TeA. Twelve VOCs were emitted at significantly higher or lower levels from TeA-treated roses compared with healthy roses. After TeA treatment, the content of 4-hydroxy-4-methyl-2-pentanone increased by 80.1% (DHSA) and 67.8% (HS-SPME) while β-elemene decreased by 84.93% (DHSA) and 71.21% (HS-SPME). Butyl acetate, allo-ocimene, decanol and tetradecanol with their relatively large contents were detected only from TeA-treated roses as early as 2–4 days after treatment with TeA. This means that theses VOCs could be used as the markers for the detection of the fungus infection in rose plants before disease symptoms become visible. The obvious temporal effects of the changes in contents of these four VOCs were also recorded. The results will help to understand the chemical mechanisms of indirect plant-mediated interactions between phytopathogens and herbivorous insects in the ternary systems.

The chemical mechanisms involved in indirect plant-mediated interactions between insects and phytopathogenic fungi on the host plant are poorly understood. Fungus-induced changes in the volatile organic compound (VOC) contents of plants need to be elucidated to address this. Here, changes in VOCs in rose (Rosa chinensis Jacq.) leaves infected with rose powdery mildew (Podosphaera pannosa [Wallr.: Fr.[ de Bary) were studied. VOCs were collected from undamaged live leaves of healthy and infected intact rose plants by dynamic headspace adsorption and identified by GC-MS. VOCs were extracted using n-hexane, and 38 chemicals were found to be produced by P. pannosa. A total of 71 VOCs not produced by P. pannosa were produced to different degrees by infected and healthy plants, and 18 of these were produced only by infected plants. Principal component analysis of chromatographic data gave VOC profiles distinguishing between infected and healthy plants. Hexadecanol, octadecanol, tetradecanol, n-butyl hexadecanoate, and n-butyl stearate dominated the VOCs produced by infected plants. These chemicals can be used as markers for detecting mildew-infected rose plants even 4-7 d after infection before symptoms appear. Clear temporal changes in the concentrations of these five chemicals were found. The results improve our understanding of the chemical mechanisms involved in interactions between insects and phytopathogenic fungi.