Health monitoring of plants by their emitted volatiles: A temporary increase in the concentration of nethyl salicylate after pathogen inoculation of tomato plants at greenhouse scale

This paper describes a method to alert growers of the presence of a pathogen infection in their greenhouse based on the detection of pathogen-induced emissions of volatile organic compounds (VOCs) from plants. Greenhouse-grown plants were inoculated with spores of a fungus to learn more about this concept. The specific objective of the present study was to determine whether VOCs are detectable after inoculation, and if so, to determine the time course of the concentrations of these compounds. To achieve this objective, we inoculated 60 greenhouse-grown tomato plants (Lycopersicon esculentum) with an aqueous suspension of Botrytis cinerea spores. Upon inoculation, the greenhouse air was sampled semi-continuously with a one hour time interval until 72 hours after inoculation (HAI). The samples were transferred to the laboratory and analysed using gas chromatography - mass spectrometry. Ten leaves were randomly selected to monitor the visible symptoms of infection. The severity of these visual symptoms was assessed at 0, 24, 48, and 72 HAI. Results demonstrated no detection of C6-compounds, and an almost constant concentration of all monoterpenes, most sesquiterpenes, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. However, the concentration of methyl salicylate increased 10-fold and 3-fold at 32 and 34 HAI respectively. At 24 HAI, 10% of the selected leaves showed mild symptoms while 20% of the selected leaves showed mild symptoms at 48 HAI. These results indicate that methyl salicylate might alert a grower of the presence of a B. cinerea infection of tomato plants at greenhouse scale. Further research is required to confirm these findings

A method to detect baseline emission and plant damage induced volatile emission in a greenhouse

The objective of this research was to ascertain if 1) baseline emission and 2) damage induced emission of volatile plant substances could be detected under greenhouse conditions. A laboratory method was validated for analysing the air in a semi-closed greenhouse with 44 m2 floor area. This greenhouse, with a volume of 270 m3, was climate controlled and light was supplied with assimilation lamps. Sixty tomato plants (Lycopersicon esculentum Mill cv. Moneymaker) were grown in this greenhouse. These plants were artificially damaged on a weekly interval by stroking the stems. Continuous flow pumps were used to purge the air surrounding the plants through tubes containing an adsorbent. This sampling step was performed before and directly after damage of the plants. After sampling, the tubes were transferred to the lab for analysis. The analysis of volatile compounds was performed using a high-throughput gas chromatography-mass spectrometry system. The method enabled the detection of baseline level emission and the emission of volatiles released after artificially damaging the tomato plants during a 6 weeks growing period. Most dominant compounds for baseline emission were the monoterpenes ß-phellandrene, 2-carene, limonene, ¿-phellandrene and ¿-pinene. Directly after damage, these compounds showed an increase of up to 100 times compared to baseline level emission. With these results, we prove that it is possible to detect baseline- and plant damage induced volatile emission in a greenhouse. This area of research is promising but more research needs to be done to determine whether it is possible to detect plant damage due to pests and pathogens using volatile sensing