Date on Master's Thesis/Doctoral Dissertation

5-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

Degree Program

Biology, PhD

Committee Chair

Emery, Sarah

Committee Co-Chair (if applicable)

Yanoviak, Stephen

Committee Member

Yanoviak, Stephen

Committee Member

Perlin, Mike

Committee Member

Abbot, Patrick

Committee Member

Schultz, David

Author's Keywords

plant volatiles; herbivores; seed priming; volatile toxicity; armyworm; plant defenses

Abstract

This dissertation explores and expands the existing knowledge on the role of plant volatiles in facilitating seed priming and providing direct defense against herbivore. Although the roles of plant volatiles in priming a plant’s defenses and providing direct defense against pests is well known, information regarding their effects on seed and the fitness of future plants and direct toxicity to herbivores is understudied. This dissertation does a thorough examination of these two understudied aspects of plant volatiles and provides novel insight into the role of plant volatiles in seed priming and direct defense (Chapter I). Seeds in the soil can be exposed to plant volatiles, however, the long-term effects of seed exposure to VOCs on growth and defenses of the germinated and growing plant are unknown. Here, I quantified the effect of seed exposure to six different plant volatiles on the growth of Arabidopsis thaliana and Medicago truncatula plants. I, also, measured the defenses of volatile exposed seed plants against herbivores of two different feeding guilds i.e., chewing insect; caterpillars and phloem-feeding insect; aphids. Seed exposure to a green leaf volatile enhanced the vii vegetative growth of Medicago and exposure to indole lead to enhanced primed defense against beet armyworm caterpillar (Spodoptera exigua) and pea aphid (Acyrthosiphon pisum) in Arabidopsis and Medicago respectively (Chapter II). Plant volatiles showed direct biocidal effects against beet armyworm caterpillars in feeding bioassay. Five of the six tested volatiles were toxic to caterpillars at concentrations ranging from 0.5 to 10 mg/ml or μl/ml. Indole and linalool were found to be the most toxic. I tested the indole toxicity against five agricultural pest caterpillars; fall armyworm (Spodoptera frugiperda), cotton bollworm (Helicoverpa zea), tobacco budworm (Heliothis virescens), velvetbean caterpillar (Anticarsia gemmatalis), and cabbage looper (Trichoplusia ni) with different host range. Indole toxicity varied with the caterpillar host range (Chapter III). In choice assays, indole spray on maize plants repelled beet armyworm caterpillar while linalool spray elicited no such response. However, both indole and linalool spray showed to reduce caterpillar feeding. Vegetative growth of maize plants was not affected by Indole or linalool spray (Chapter IV). Collectively, this work reveals the role of plant VOCs in seed priming and improves our understanding of direct toxicity of plant volatiles against herbivores which have the potential to be used for pest control.

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