| Volatile organic compounds (VOCs) are a small portion of the total metabolites produced by organisms; however, their unique properties enable them to mediate important biological functions, especially in aerial and terrestrial environments. In agriculture, the potential uses of VOCs include volatile-mediated inhibition of pathogen growth and increased plant systemic resistance. Filamentous fungi in the genus Trichoderma are robust biological control agents as they utilize several modes of action including resistance, antibiosis, competition and myco-parasitism. Earlier work by our laboratory demonstrated the ability of Trichoderma-derived VOCs to stimulate Arabidopsis growth.;In this dissertation, Trichoderma emission profiles, concentrations, quantities, and VOC-mediated effects on plants were measured in order to develop a mechanistic understanding of the volatile-mediated Trichoderma-to-plant interactions. Trichoderma volatile-mediated plant growth promotion was dependent on the age of the fungal culture, developmental stage of the plant, duration of the exposure, and was isolate-specific. Screening of 20 Trichoderma isolates for VOC-induced growth of Arabidopsis identified 9 growth promoting isolates increasing plant biomass (up to 41.6%) and chlorophyll content (>89.3%). In addition, similar responses to VOC mixtures were obtained in tomatoes, i.e. a significant increase in plant biomass (>99%), larger plant size, and significant development of lateral roots, suggesting that plant growth promotion may occur through a similar mode of action in different types of plants. GC-MS analysis of VOCs from Trichoderma isolates led to identification of more than 147 unique compounds and several unknown sesquiterpenes, diterpenes, and tetraterpenes.;After VOCs were identified from GC-MS data, 26 compounds were selected and tested individually on Arabidopsis in order to determine if individual compounds could mimic the effects of Trichoderma volatile mixtures on plant growth. Of the compounds tested, exposure to 1-decene yielded increased seed germination, plant fresh shoot weight (>38.9%), and chlorophyll (>67.8%). RNA sequencing analysis of Arabidopsis shoots treated with 1-decene for 72 hours identified 123 differentially expressed genes involved in volatile responses. Up-regulated genes were related to growth, responses to hormone and cell wall modifications inducible by auxin. The RNA-seq data provides a list of candidate genes to screen in future research on the biological activities of fungal VOCs. |
