Preliminary studies on the allelopathic potential of two invasive species of Solidago against selected cereal weeds

The European Union is currently pursuing a policy of moving away from synthetic plant protection products to natural ones. This is reflected in the search for natural substances that can replace them in agricultural production. Many studies indicate that invasive species of Solidago have such allelopathic potential. The aim of the study was to assess the effect of extracts of two Solidago species (Solidago gigantea L. and Solidago canadensis L.) on the growth and development of cereal weeds: Chenopodium album, Papaver rhoeas and Agrostemma githago. Using liquid chromatography coupled with mass spectrometry (LC - MS) techniques, the material (crude extract, phenolic and saponins fraction) was standardized and tested for allelopathic activity using the modified first generation biotest. The results indicate the phenolic fraction (20.04 mg/g dry weight of Solidago gigantea; 21.03 mg/g for Solidago canadensis) and saponin fraction (2.27 and 3.74 mg/g dry weight respectively). Both fractions from S. gigantea are characterized by high phytotoxicity in relation to Ch. album, causing over 90% reduction of its biomass in relation to the control. For P. rhoeas these differences are not so clear. Biomass reduction by the phenolic fraction was 20% and by the saponin fraction 50%. In the case of S. canadensis, allelopathic activity was not as pronounced and ranged from 20–40% for the saponin fraction relative to the P. rhoeas. The highest resistance to preparations made from both species of Solidago was demonstrated by A. githago.