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.
