Abstract
Plant chemistry is an important contributor to the interaction with herbivores. Here, we report on a previously unknown role for foliar and glandular trichome volatiles in their interaction with the specialist herbivore of solanaceous plants, the tomato red spider mite Tetranychus evansi. We used various bioassays and chemical analyses including coupled gas chromatography-mass spectrometry (GC/MS) and liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-QToF-MS) to investigate this interaction between cultivated African nightshades and T. evansi. We show that, whereas morphologically different cultivated African nightshade species released similar foliar volatile organic compounds (VOCs) that attracted T. evansi, VOCs released from exudates of ruptured glandular trichomes of one nightshade species influenced local defense on the leaf surface. VOCs from ruptured glandular trichomes comprising mainly saturated and unsaturated fatty acids deterred T. evansi oviposition. Of the fatty acids, the unsaturated fatty acids accounted for >40% of the oviposition deterrent activity. Our findings point to a defense strategy in a plant, based on opposing roles for volatiles released by foliar and glandular trichomes in response to attack by a specialist herbivore.
Highlights
The evolutionary arms race between plants and herbivorous arthropods has been studied extensively in the past, demonstrating that plants use a variety of defensive systems against attacking herbivores [1,2,3,4,5]
We found that odors released by different African nightshade species attracted T. evansi but in a variable pattern (Fig 1a and 1b)
Despite these differences, when the plants were compared in paired assays, T. evansi did not show a significant preference for any of the odors of these African nightshade species (S. sarrachoides vs. S. scabrum: P = 0.18; S. sarrachoides vs. S. villosum: P = 0.21; S. villosum vs. S. scabrum: P = 0.33) (Fig 1b)
Summary
The evolutionary arms race between plants and herbivorous arthropods has been studied extensively in the past, demonstrating that plants use a variety of defensive systems against attacking herbivores [1,2,3,4,5]. Experimental evidence has shown that herbivores can overcome these defenses through a variety of ways including avoidance [6] and/or suppression of the induction of the defense system especially through the use of various chemicals [7,8]. An example of a plant defense system against herbivory is trichomes, which vary in type, shape and mechanism of action. Glandular trichomes produce sticky secretions from their glandular heads to disable small herbivorous arthropod movement and feeding [9,10,11]
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