Volatile emissions of Puccinia triticina infected wheat and its effect on uninfected wheat seedlings
Castelyn, Howard Dean
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Plants emit a vast array of volatile organic compounds to which surrounding plants can respond. Recent research suggested volatile signalling between leaf rust (Puccinia triticina Erikss.) infected and uninfected wheat (Triticum aestivum L.). The current project was undertaken to further investigate these putative events. Uninfected wheat was exposed to volatiles emitted by leaf rust infected wheat in a continual air flow system. Different combinations of resistant (Thatcher+Lr9) and susceptible (Thatcher) wheat lines were used for the volatile exposure experiments. When susceptible seedlings were exposed to volatiles from either resistant or susceptible plants there was a significant decrease in percentage leaf area infected and pustule size after a subsequent infection with leaf rust. The volatile exposure was also linked with an induced defence response as confirmed with increased enzyme activity and gene expression. Generally, an induction of β-1,3-glucanase activity was observed at 8 hours post exposure in exposed resistant and susceptible seedlings regardless of the infected line that released the volatiles. Pathogen-related protein 2 gene expression was also induced at 8 hours post exposure in both lines exposed to volatiles released by infected resistant seedlings but not in those exposed to infected susceptible seedling volatiles. This induction of the defence response could only be attributed to volatiles emitted by infected wheat seedlings. Emitted volatiles were captured by solid phase micro-extraction and classified by gas chromatography mass spectrometry. Infected resistant seedlings released a number of unique volatiles including ocimene that was not observed in both the mock infected resistant or infected and mock infected susceptible seedlings. Fewer unique volatiles were observed in the infected susceptible seedlings compared to the mock infected susceptible seedlings with green leaf volatiles being common in both treatments. Some of the identified volatiles were previously linked to the defence response in plants.