Allelopathic potential of Chrysanthemoides monilifera subsp. monilifera (boneseed): a novel weapon in the invasion processes.
Natural ecosystems and primary production industries are threatened by invasive plant species, and allelopathy is one of the attributes that may assist in the invasion process. We studied the allelopathic potentiality of Chrysanthemoides monilifera subsp. monilifera (boneseed), one of the seven priority weeds identified for the development of predictive modeling in the world. A series of bioassays compared dose-response to aqueous extracts of boneseed as well as the impact of leachate on model (Lactuca sativa) and associated species (Isotoma axillaris and Acacia mearnsii) with particular reference to biometric, physiological and biochemical parameters. We found total phenolics in the order of leaf > root > stem > infested soil > outside soil. Acetone extracted more phenolics than other solvents, and air-dried double-centrifuged dominates over oven-dried single-centrifuged processing methods. Generally, aqueous extracts of boneseed organs showed ranked inhibition similar to phenolic content on germination indices and biometric parameters of both model and associated species, although, the hypocotyl length and weight response were varied. Dose response studies showed a strong correlation of aqueous extract concentration with both hypocotyl and radical length of I. axillaris even at low concentrations providing evidence of the allelopathic potential of boneseed. I. axillaris was the most susceptible species showing LC50 of 0.46%, 0.89% and 0.86% in response to leaf, stem and root extract respectively. Water uptake and carbohydrate metabolism of L. sativa seeds were gradually decreased with increasing extract concentrations. Hydrogen peroxide was increased with increasing extract concentration along with acceleration of electrolytic leakage and lipid peroxidation in L. sativa seedlings, providing evidence of cellular fragmentation suggesting a mechanism of allelopathic impact through excessive reactive oxygen species (ROS) production. Overall, leaf extracts showed more phytotoxicity when compared with other organs of boneseed. These findings help to explain the mechanism of invasion by boneseed and emphasize the importance of mitigating the effects of allelopathy by boneseed to protect native and crop species.