Ivana Bjedov1, Dragica Obratov-Petković1, Marija Nešić1, Dragana Skočajić1, Uroš Gašić2 and Danijela Mišić3
1University of Belgrade, Faculty of Forestry, Kneza Višeslava 1, 10030 Belgrade, Serbia
2University of Belgrade, Faculty of Chemistry, P.O. Box 51, 11158 Belgrade, Serbia
3University of Belgrade, Institute for Biological Research “Siniša Stanković”, Bulevar despota Stefana 142, 11060 Belgrade, Serbia
Johnson grass, Sorghum halepense (L.) Pers., is recognized as a globally successful invader and one of the most aggressive weeds in Europe. According to data from 2012 this species had the status of a sporadically invasive species in Serbia. Since then, S. halepense has been increasing in frequency and range. Its populations are widespread and numerous, which represents a strong pressure on autochthonous flora and vegetation. Considering all the aforementioned, the revision of S. halepense status of invasiveness for Serbia is necessary, in order to improve management strategies for this invasive species.
It is known that the allelopathic effects of plant secondary metabolites present a potential mechanism of invasive plant success. High concentrations of phenolic compounds, with their diverse functionality, may confer an advantage to plants in response to environmental conditions.
With the aim to examine the chemodiversity of S. halepense in Belgrade (Serbia) urban areas, we performed UHPLC/DAD/MS2 targeted metabolomic analysis of leaves, rhizomes and inflorescences of plants originating from 5 localities. These populations are located in the wider area of Belgrade, from urban and suburban zones. One population from Montenegro was used as outgroup. The analysis was targeted towards 19 polyphenolic compounds: 9 phenolic acids, 6 flavonoid aglycones and 4 flavonoid glucosides. Phenolic acids were recognized as the dominant group of polyphenolics in samples, with chlorogenic acid being the major compound in inflorescences and leaves, while in rhizomes p-hydroxybenzoic acid predominated. The third and fourth most abundant compounds in samples were p-coumaric acid and protocatechuic acid, respectively. Flavonoids were less abundant in the analysed S. halepense samples. Interestingly, the amount of flavonoid aglycones (quercetin and luteolin) and flavonoid glycosides (quercetin 3-O-rutinoside, quercetin 3-O-glucoside, isorhamnetin 3-O-rutinoside, and isorhamnetin 3-O-rutinoside) were the highest in inflorescences. The results pointed to the considerable differences in polyphenolics composition among plant organs. In addition, inter-population variability was also recognized. As revealed by the PCA, the population originating from Montenegro was well distinguished from the Belgrade populations based on the metabolite profiles. In addition, population 1 (i.e. population from Jakovo) was distinguished from the rest of Belgrade populations.
Considering the high diversity and amount of polyphenolic compounds identified in S. halepense, and their known phytotoxic and allelopathic effects, it might be presumed that these compounds, at least partially contribute to fast-spreading of Johnson grass in the urban and suburban areas of Belgrade. To take advantage of this species invasiveness, we propose the usage of S. halepense methanol extracts as bioherbicides for the effective and environmentally sustainable weed control. Further studies should be conducted in order to test these possibilities.