Response of stored grain insect pests and barley to ozone treatment

Ozone (O3) has distinct advantages over other stored grain pest treatments, such a toxicity to a broad range of organisms and rapid auto-decomposition to oxygen without leaving residues, making it a promising fumigant to protect stored grains. This research project focused on understanding how stored grain insects and barley respond to ozone. Several studies have assessed the efficacy of O3 against pests in stored maize and wheat grain, but little is known about the toxicity of O3 on stored grain pests in barley and its effects on barley quality and germination. My results indicated that more than 2 days of ozone treatment should be considered as the endpoint to evaluate insect mortality rate due to delayed toxicity of O3. C×t product 36 mg h/L (700ppm × 24 h) offered complete mortality for all stages of the two species tested insects R. dominica and T. castaneum, without affecting barley commercial quality. As barley is to be used for malting purposes, it is important to understand that effect of ozone on barley germination, whether positive or negative. Relevant short period treatment (20 min) with ozone at 700ppm can facilitate barley germination, but it was adversely impacted for longer O3 exposure times, such as 24 h. Ozone treated barley seed released a greater number and quantity of volatile organic compounds (VOCs). However, alcohols and hydrocarbons gradually decreased, whereas aldehydes and organic acids markedly increased with increasing time of ozone treatment. Acetic acid was identified as a potential ozone stress-specific marker. Furthermore, the dosage-dependent function of acetic acid on barley germination was verified and results indicated that low dosage (0.05 - 0.5 mg/g of barley) of acetic acid could lead to increasing germination rate. Potential chemical biomarkers from barley seeds during germination were identified using gas chromatography mass spectrometry (GC/MS). Statistical assessment of the data via principal component analysis demonstrated that the metabolic changes during germination were reflected by time-dependent shifts. Alcohols, fatty acids and ketones were the major contributors to the time-driven changes during germination. In addition, ozone induced an increase in fatty acids at the early stage of barley germination and probably enhanced germination by supplying carbon skeletons and energy for germination via the TCA cycle. My results indicate that ozone could be utilized to improve the quality of malting barley on enhancing germination rate. The key finding is that acetic acid could be used as a regulator to control germination. Moreover, this PhD study is the first-time explored effect of O3 on metabolite profiles of barley germination, which could lead to identifying the factors might impact barley germination or malt quality