Abstract Model Greensys2007

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 m floor area. This greenhouse, with a volume of 270 m, 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 β-phellandrene, 2-carene, limonene, α-phellandrene and α-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 baselineand 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. INTRODUCTION Early detection and location of plant damage due to pests and pathogens is a major challenge in commercial greenhouse cultivation. It allows the crop manager to perform site-specific actions instead of full field treatment. This will reduce the use of pesticides. Previous laboratory experiments have revealed that sensing volatiles released by the damaged plants might offer a powerful technique to monitor the status of greenhouse crops. Such laboratory experiments that confirm the change of volatile substances released after damage are not new (e.g. Heiden et al., 2003). A common method used in such studies is the use of dynamic sampling to concentrate the volatiles of interest and thereafter gas chromatography coupled to mass spectrometry for analysis. However, the validation of such method to detect plant induced volatiles in a greenhouse has not been practiced until now. 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. The primary research question related to this objective is whether dynamic sampling and gas chromatographic mass spectrometric analysis allows the identification of plant induced volatiles in a greenhouse. Additionally we checked whether this method allows the monitoring of plant damage induced volatiles. 1415 Proc. IS on Greensys2007 Eds.:S. De Pascale et al. Acta Hort. 801, ISHS 2008 MATERIALS AND METHODS Plant Material Seeds of tomato plants (Lycopersicon esculentum Mill) of the cultivar Moneymaker were germinated in a standard greenhouse at 20°C and 50% relative humidity. When plants were about 7 weeks of age, 60 plants were transferred to a semiclosed greenhouse. At that age the individual plants were about 80 cm tall. In this semiclosed greenhouse the plants remained until the age of 12 weeks. During this time period of 6 weeks, on Wednesday, plants were winded, and flowers were pollinated using a vibrating device. During the time period of 6 weeks, on Thursday, plants were artificially damaged by stroking the full length of the stem of each individual plant using a stainless steel bar. Also the length of 3 randomly selected plants was measured during the time period of 6 weeks, on Thursday, to estimate the growth of the plants in the semi-closed greenhouse. We used 3 independent replicate studies for this paper. The first study was from February – March, the second from April – May and the third from June – July. Greenhouse The semi-closed greenhouse used for the experiments has been described by Körner et al. (2007). In short, a closed greenhouse with 44 m floor area was used. The total volume of this greenhouse including basement was 270 m. The greenhouse was sealed to minimize ventilation (~ 0.7 mol of air per second). Electrical heating and direct mechanical cooling situated in the basement controlled temperature and humidity. The temperature was set at 22°C during day and 16°C during the night. Assimilation lamps were installed. These lamps turned on when radiation outside the greenhouse dropped below 150 W/m and turned off when the radiation outside increased over 250 W/m. The relative humidity inside the greenhouse was maintained to about 70% during the day and 90% during night. Temperature and relative humidity of the air in the greenhouse was measured with dry and wet bulb platinum resistance temperature detectors. A third sensor measured temperature and relative humidity for climate control purposes. Pure CO2 was injected into the greenhouse proportionally to the difference between measured CO2 concentration and the CO2 set point using an infrared gas analyser and a mass-flow controller to maintain a CO2 concentration of 420 ppm throughout the experiments. Air Sampling for Volatile Analysis Continuous flow pumps were used to purge 6 liters of air surrounding the plants through stainless steel tubes (Markes international Ltd, UK) containing 200 mg of tenaxTA 20/35 (GraceAlltech, Breda, The Netherlands). Air was sucked through these tubes at 300 ml/min during 60 minutes. This sampling step was performed before and directly after damage of the plants at a fixed starting time point i.e. 13.00 h. The air was sampled at 3 locations within the greenhouse to provide insight into the spatial distribution of volatile substances inside the greenhouse. These 3 sampling points were located in the left-rear, centre and right-front location of the greenhouse at a height of 1 m. After sampling, the tubes were immediately capped and transferred to the lab for analysis. Gas Chromatography – Mass Spectrometry The analysis of volatile compounds was performed using a high-throughput gas chromatography / mass spectrometry system (GC-MS). Before analyses the tubes were dry-purged with helium at ambient temperature with a flow of 100 ml/min for 10 minutes to remove unwanted water. The high-throughput headspace analysis method was developed on a Trace GC UltrA (Thermo Electron Corporation, Auston, TX USA) equipped with a Trace DSQ quadrupole mass spectrometer (Thermo Electron Corporation, Auston, TX USA). Samples were transferred from the trap using a thermal desorption system (TDS) at 250°C for 5 min (UltrA-TD, Markes international LTD, UK). Analytes were then transferred to an electronically-cooled focusing trap at -5C (Unity, Markes international LTD, UK). Analytes were transferred to the column by