Plants are attacked by a variety of (micro)organisms. In order to cope with potential attackers many plants synthesize a diversity of repellent, deterrent and/or toxic compounds. Pyrrolizidine... Show morePlants are attacked by a variety of (micro)organisms. In order to cope with potential attackers many plants synthesize a diversity of repellent, deterrent and/or toxic compounds. Pyrrolizidine alkaloids (PAs) are a well-known class of defense compounds, abundantly found in species of Senecio and Jacobaea. The objectives of the study were to acquire knowledge on the PA composition of plants and its interaction with soil-borne microorganisms. In order to do so, a more sensitive, PA-analysing method was applied, which allowed us to distinguish between PAs in tertiary amine and N-oxide form. The tertiary PA form is known to have a more negative effect on generalist insects. Our study clearly showed that high levels of tertiary PAs occur in Jacobaea vulgaris and not caused by an artefact as suggested in previous studies. Green-house experiments showed that the PA composition below- and aboveground was significantly aff ected by both soil-type and soil-inoculum. The inoculum-induced PA composition aboveground did affect thrips resistance for one J. vulgaris genotype. Experiments also showed that the fungal community did depend on the PA composition of the plant while this had less or no effect on bacterial and mycorrhizal communities in roots and rhizosphere soil. Show less
Native and invasive individuals of Jacobaea vulgaris differ from each other in a number of traits related to defence and growth. Two separate studies with different genetic markers and partly also... Show moreNative and invasive individuals of Jacobaea vulgaris differ from each other in a number of traits related to defence and growth. Two separate studies with different genetic markers and partly also with different individuals both reveal that the most likely scenario of invasive J. vulgaris individuals is that they originated from multiple source populations. The chance of preadaptation is very little because it is very unlikely that all these different source populations al contained individuals that were already adapted to the new environment. The introduction of different source populations and the admixture of individuals from different populations have likely contributed to the fast evolution of J. vulgaris. Admixture increased the genetic variation and has also lead to recombination of native individuals that were isolated from each other in the native area.. The invasive character of Jacobaea vulgaris is especially expressed by the lower root- shoot ratio. With this change the competition with local species is increased. Bigger shoots leads to a higher photosynthetic capacity and more growth. Besides, within J. vulgaris plant size is positively correlated with the amount of seeds produced. As a result of this, spread and abundance of J. vulgaris easily increases. Show less
