Effects of ‘Candidatus Phytoplasma asteris’ on the Volatile Chemical Content and Composition of Grindelia robusta Nutt.

Grindelia robusta, a perennial herb, contains an essential oil that is employed as an antitussive, sedative, and analgesic agent. During the Spring of 2007, ‘Candidatus Phytoplasma asteris’-related phytoplasmas were identified in plants showing virescence and phyllody symptoms. The qualitative and quantitative composition of volatiles of the oil of healthy and infected plants were compared by Gas Chromatography/Mass Spectrometry analyses. Samples from 6 symptomatic and 5 asymptomatic plants were tested by nested PCR followed by RFLP analyses confirmed the presence of ‘Ca. P. asteris’ in all symptomatic samples. The oils from healthy and infected plants, obtained by steam-distillation, contained 42 components; that of healthy plants contained a higher concentration of monoterpenes, especially limonene and bornyl acetate, which were nearly 50% higher.