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Title: Duration of emission of volatile organic compounds from mechanically damaged plant leaves

item Smith, Lincoln
item Beck, John

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2015
Publication Date: 8/21/2015
Citation: Smith, L., Beck, J.J. 2015. Duration of emission of volatile organic compounds from mechanically damaged plant leaves. Journal of Plant Physiology. 188, 19-28.

Interpretive Summary: Invasive alien weeds are an increasing problem affecting many agricultural and natural ecosystems. Classical biological control, the introduction of exotic natural enemies, is a principal strategy for controlling invasive alien weeds. However, to prevent possible risk to nontarget species, it is critical to determine the host plant specificity of prospective biological control agents. This is currently done by performing choice or no-choice behavioral experiments using plants in the laboratory or under field conditions. The results of such experiments are empirical, indicating which plants are acceptable or suitable for a prospective agent under specific experimental conditions; however, they do not answer the question why some plants are acceptable and others are not. In situations where a nontarget plant may be suitable for development of a prospective agent in laboratory experiments, but the plant is not attacked under normal field conditions, understanding why the herbivore is so selective in the field could help improve our assessment of its potential risk to the nontarget plant. Some volatile organic compounds (VOC) emitted from plants are known to act as attractants or repellants to insects. However, only recently have scientists begun to study the role of VOCs for classical biological control of weeds. These studies have typically involved undamaged plants; however, the effects of prior damage on qualitative and quantitative emission of VOCs is not known. Because both olfactory and gustatory stimuli may be important in host plant selection, studies of undamaged plants may overlook VOCs that are released only after damage. Our results showed that damaging plants increased the number of VOCs emitted and changed which compounds are important for distinguishing between three plants, thus insects are likely to respond differently to undamaged versus damaged plants. Furthermore these changes persist for at least 48 hours after physical damage to the plants.

Technical Abstract: Classical biological control of invasive alien weeds depends on the use of arthropod herbivores that are sufficiently host specific to avoid risk of injuring nontarget plants. Host plant specificity is usually evaluated by using a combination of behavioral and developmental experiments under choice, no-choice and field conditions. Secondary plant compounds are likely to have an important influence on host plant specificity. However, relatively little is known about the volatile organic compounds (VOCs) that are emitted by target and nontarget plants, and how environmental conditions may affect their emission. Previous studies have shown that mechanical damage of leaves increases the composition and content of VOCs emitted. In this study we measured the VOC emissions of five species of plants in the subtribe Centaureinae (Asteraceae) – Carthamus tinctorius, Centaurea cineraria, C. melitensis, C. rothrockii, and C. solstitialis – that have previously been used in host specificity experiments for a prospective biological control agent of yellow starthistle (Centaurea solstitialis). Leaves of each plant were punctured with a needle and the VOCs were collected by solid-phase microextraction (SPME) periodically over 48 h and analyzed by GC-MS. A total of 49 compounds were detected. Damage caused an immediate increase of 200 to 600% in the composition of VOCs emitted from each plant species, and the amounts generally remained high for at least 48 h. The results indicate that a very unspecific mechanical damage can cause a prolonged change in the VOC profile of plants.