No abstract

Common ragweed (Ambrosia artemisiifolia L.) is an annual Asteraceae species native to North America which is highly invasive across Europe and has harmful impacts, especially on human health and agriculture. Besides its wide ecological range, particularly its high reproductive power by seeds is promoting its spread to various habitats and regions. To prevent further spread and to control the plant, the European Commission funded projects and COST-Actions involving scientists from all over Europe. A joint trial was set up comprising eight different laboratories from Europe to study seed viability variation in different seed samples. Three different testing methods (viability test with 2,3,5-triphenyltetrazolium chloride (TTC), a germination test combined with a subsequent TTC test and a crush test) were tested within the EU-COST-Action SMARTER network to four different seed origins. The viability test results from different laboratories were compared for variation amongst tests and laboratories. The main aim was to optimise the reliability of testing procedures, but results revealed not only significant effects of seed origin and seed age on seed viability, but also considerable differences between the output of the individual testing methods and furthermore between laboratories. Due to these significant differences in the results of the testing labs, additionally a second test was set up. Twelve Austrian ragweed populations were used for TTC testing to obtain a precise adjustment of the testing method as well as a tight guideline for interpreting the results, particularly for the TTC state “intermediate” since a proper classification of TTC-intermediate coloured seeds is still a challenge when determining viability rates.

Ambrosia artemisiifolia L. (Asteraceae), known as common ragweed, is an annual herbaceous species native to North America that has become one of the most economically important weeds in arable fields throughout Central Europe. Its large ecological amplitude enables the species to become established in several types of environments, and management options to effectively contain its spread are limited due to a lack of efficacy, high cost, or lack of awareness. In the last decade, in particular, soybean fields have been severely affected by common ragweed invasion. However, until now, information on the yield-decreasing effects of the plant has been scarce. Therefore, the aim of this study was to evaluate the competition effects of common ragweed on (1) soybean growth (aboveground/belowground), (2) the yield of two different soybean cultivars, and (3) the nodulation potential. Based on a greenhouse and biennial field trial, we found that in plots with the highest common ragweed biomass, the soybean yield loss accounted for 84% compared to the weed-free control, on average. The number of nodules, in addition to the mean nodule weight, which are tightly correlated with soybean yield, were significantly reduced by the presence of common ragweed. Just one common ragweed plant per square meter reduced the number of nodules by 56%, and consequently led to a decrease in yield of 18%. Although it has been reported that the genus Ambrosia produces and releases several types of secondary metabolites, little is known about the influence of these chemical compounds on soybean growth and nodulation. Thus, there is substantial need for research to understand the mechanisms behind the interaction between common ragweed and soybean, with a view to finding new approaches for improved common ragweed control, thereby protecting soybean and other crops against substantial yield losses.

No abstract

Following the novel weapon hypothesis, the invasiveness of non-native species, such as common ragweed (Ambrosia artemisiifolia L.) can result from a loss of natural competitors due to the production of chemical compounds, which negatively affect native communities. Particularly the genus Ambrosia produces several types of organic compounds, which have the potential to inhibit germination and growth of other plants. Subsequent to an assessment of the chemical content of three different ragweed extracts (aqueous shoot and root extracts, as well as essential oil), two different trials on the effects of different concentrations of these extracts, as well as ragweed residues, were conducted on two different mediums (Petri dish vs. soil). In addition, we investigated the impact on the infection potential of Bradyrhizobium japonicum on soybean roots in three different soil types (arable soil, potting soil, and sand). The results showed that the exposure to common ragweed extracts and residues induced changes in the biomass and root production of crops and ragweed itself. Even though crops and ragweed differed in their response behavior, the strongest negative impact on all crops and ragweed was observed with ragweed residues, leading to reductions in biomass and root growth of up to 90%. Furthermore, we found a decrease in the number of rhizobial nodules of up to 48% when soybean was exposed to ragweed root extract.