The effect of environmental conditions on the seasonal dormancy pattern and germination of weed seeds

Weeds cause considerable losses in horticultural and agricultural crops. Weeds are still predominantly controlled with herbicides. To reduce the use of chemicals, a better understanding of the biology of weeds is required. In this thesis the effect of environmental conditions on dormancy and germination of Chenopodium album L., Polygonum persicaria L., P. lapathifolium L. subsp. lapathifolium, Sisymbrium officinale (L.) Scop. and Spergula arvensis L. was investigated.It was shown that changes in dormancy of these species were regulated by temperature. Soil moisture and nitrate content did not affect these changes. The dormancy status of the seeds was visualized by the range of temperatures over which germination of exhumed seeds was possible. During relief of dormancy, seeds could germinate over a progressively wider range of temperatures. During induction of dormancy, this range became narrower.Germination of C.album, S. officinale and S.arvensis was stimulated by light, nitrate and desiccation. These factors all increased the width of the range of temperatures over which germination could proceed and therefore affected the expression of dormancy. That is, seeds seemed less dormant and they could germinate during a longer period of the year. Endogenous nitrate, that entered the seeds via the mother plant during seed development, only temporarily stimulated germination. After burial the effect disappeared because of equalization of the nitrate content. The effect of desiccation was stronger, the more seeds were desiccated.With descriptive models the changes in the range of germination temperatures of the investigated species and the effect of nitrate upon these changes were simulated for a period of three years as a function of soil temperature during burial. When the field temperature after exhumation and the germination-temperature range overlapped, germination was possible. Accordingly, temperature had a dual effect. Germination depended on the one hand on the actual field temperature after exhumation , on the other hand on the width of the germination-temperature range, which was determined by the dormancy status of the seeds and was regulated by soil temperature during burial . When nitrate was added during the test, the germinationtemperature range became wider and germination could occur during a longer period of the year

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