Bioactivity of glandular trichome exudates obtained from <i>Solanum sarrachoides</i> and tested on <i>Tetranychus evansi</i> females.

(a) Oviposition deterrent activity of glandular trichome components of Solanum sarrachoides to T. evansi. Untreated leaf disks of S. scabrum were used as control in bars I, II and III. Filter paper arenas treated with dichloromethane and methanol were used as control in bars IV and V. Representative chromatograms of chemical components present in glandular trichome exudates dissolved in dichloromethane from: (b) Solanum sarrachoides. Peak no: 1 = 2-undecanone; 2 = decanoic acid; 3 = undecanoic acid; 4 = dodecanoic acid; 5 = myristoleic acid; 6 = tetradecanoic acid; 7 = pentadecanoic acid; 8 = palmitoleic acid; 9 = hexadecanoic acid; 10 = heptadecanoic acid; 11 = linoleic acid; 12 = oleic acid; 13 = octadecanoic acid and (c) S. villosum; and (d) representative chromatogram of chemical components present in glandular trichome exudates of S. sarrachoides dissolved in methanol; Compound no. 1 = quercetin; 2 = 6-hydroxyluteolin; 3 = hesperetin.</p

Concentrations of fatty acids and 2-undecanone in the blend tested in bioassays.

<p>Concentrations of fatty acids and 2-undecanone in the blend tested in bioassays.</p

Olfactory responses of <i>Tetranychus evansi</i> females to intact plant volatile odors of three African nightshade species.

<p>(a) Intact plants compared to air (control); and b) Pairwise comparisons of intact plants. Responses are expressed as preference indices (PI); * = significant; ns = not significant (α = 0.05).</p

Opposing Roles of Foliar and Glandular Trichome Volatile Components in Cultivated Nightshade Interaction with a Specialist Herbivore

<div><p>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 <i>Tetranychus evansi</i>. 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 <i>T</i>. <i>evansi</i>. We show that, whereas morphologically different cultivated African nightshade species released similar foliar volatile organic compounds (VOCs) that attracted <i>T</i>. <i>evansi</i>, 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 <i>T</i>. <i>evansi</i> 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.</p></div

Representative chromatograms of chemical components identified in foliar volatiles of three African nightshade species <i>viz</i>. <i>Solanum sarrachoides</i>, <i>S</i>. <i>scabrum</i> and <i>S</i>. <i>villosum</i>.

<p>Peak no: 1 = hexanal; 2 = (<i>Z</i>)-3-hexen-1-ol; 3 = (+)-α-Pinene; 4 = benzaldehyde; 5 = (-)-β-Pinene; 6 = 6-methyl-5-hepten-2-one; 7 = β-myrcene; 8 = octanal; 9 = (<i>S</i>)-(-)-limonene; 10 = undecane; 11 = dihydromyrcenol; 12 = methyl benzoate; 13 = linalool; 14 = nonanal; 15 = isophorone; 16 = octanoic acid; 17 = α-terpineol; 18 = dodecane; 19 = decanal; 20 = carvacrol, methyl ether; 21 = pentadecane; 22 = bornyl acetate; 23 = hexadecane; 24 = copaene; 25 = β-elemene; 26 = longifolene; 27 = (−)-α-cedrene; 28 = (<i>E</i>)-β -caryophyllene; 29 = (+)-β-cedrene; 30 = geranyl acetone; 31 = α-humulene; 32 = butylated hydroxytoluene; 33 = δ-cadinene; 34 = caryophyllene oxide; 35 = cedrol; 36 = hexadecanoic acid.</p

Abundance and behavioral responses of <i>Tetranychus evansi</i> to chemical components detected in intact plants of the three African nightshade species.

<p>(a) Abundance of compound classes detected from foliar scents of <i>Solanum sarrachoides</i>, <i>S</i>. <i>scabrum</i> and <i>S</i>. <i>villosum</i>; (b) olfactory response of <i>Tetranychus evansi</i> to individual compound classes and a blend of all the classes. All responses were compared to a control and expressed as preference indices; * = significant (α = 0.05).</p

Effect of chemical components detected in trichome exudates of <i>S</i>. <i>sarrachoides</i> on oviposition deterrence activity of <i>Tetranychus evansi</i>.

<p>(a) Oviposition deterrence index (ODI) on filter paper arenas treated with blends of 2-undecanone (2-UND), saturated fatty acids (SFA) and unsaturated fatty acids (UNSFA) detected in glandular trichome exudates of <i>S</i>. <i>sarrachoides</i>. (b) Oviposition deterrence index on filter paper arenas treated with a full blend constituting; (I) 2-undecanone, saturated and unsaturated fatty acids at 1000 ng μL^-1 and; (II) a varied concentration of the unsaturated fatty acids at 10 ng μL^-1 whereby 2-undecanone and saturated fatty acids were maintained at 1000 ng μL^-1.</p

Authentic volatile compounds and their concentrations in the class blend tested in bioassays.

<p>Authentic volatile compounds and their concentrations in the class blend tested in bioassays.</p

χ² and p-values associated with the response of adult females of <i>Tetranychus evansi</i> to synthetic blends of compound classes identified from three African nightshades species.

<p>χ² and p-values associated with the response of adult females of <i>Tetranychus evansi</i> to synthetic blends of compound classes identified from three African nightshades species.</p

Table_1_Non-host plant odors influence the tritrophic interaction between tomato, its foliar herbivore Tuta absoluta and mirid predator Nesidiocoris tenuis.docx

The tomato leafminer, Tuta absoluta is a destructive invasive pest of cultivated tomato and other Solanaceae plants, with yield losses of 80-100%. Mirid predators are key natural enemies of T. absoluta, but they also feed on host plants in the absence of their prey. Management of T. absoluta is a challenge due to its high biotic potential, resistance to many insecticides and the absence of sufficiently adapted auxiliary fauna in its new dispersion zones. Olfaction plays an important role in the tritrophic interaction between tomato, its herbivore pest T. absoluta and its mirid predators, which can be influenced by non-host plant odors. However, how non-host odours shape this interaction is poorly understood. Previously, we had demonstrated belowground crop protection properties of certain Asteraceae plants against the root-knot nematode Meloidogyne incognita, pest of tomato and other Solanaceae plants. Additionally, Asteraceae plants impact negatively on feeding behavior of above-ground pests of Solanaceae plants, including the greenhouse whitefly (Trialeurodes vaporariorum) and green peach aphid (Myzus persicae). Here, we tested the hypothesis that foliar volatiles from some of these non-host Asteraceae plants can influence the tomato-T. absoluta-mirid predator tritrophic interaction. In olfactometer assays, T. absoluta females were attracted to volatiles of the Solanaceae host plants tomato and giant nightshade but avoided volatiles of the Asteraceae plants, blackjack and marigold, and the positive control, wild tomato, when tested alone or in combination with the host plants. Coupled gas chromatography-mass spectrometry analysis showed that host and non-host plants varied in their emission of volatiles, mainly monoterpenes and sesquiterpenes. Random forest analysis combined with behavioral assays identified monoterpenes as the host plant attractive blend to T. absoluta and its mirid predator, with sesquiterpenes identified as the non-host plant repellent blend against T. absoluta. Contrastingly, the mirid predator was indifferent to the non-host plant repellent sesquiterpenes. Our findings indicate that terpenes influence the tomato-T. absoluta-mirid predator tritrophic interaction. Further, our results emphasize the importance of studying crop protection from a holistic approach to identify companion crops that serve multi-functional roles.</p