Identification and phytotoxicity assessment of phenolic compounds in Chrysanthemoides monilifera subsp. Monilifera (boneseed)

Abstract

Chrysanthemoides monilifera subsp. monilifera (boneseed), a weed of national significancein Australia, threatens indigenous species and crop production through allelopathy. We aimed to identify phenolic compounds produced by boneseed and to assess their phytotoxicityon native species. Phenolic compounds in water and methanol extracts, and in decomposed litter-mediated soil leachate were identified using HPLC, and phytotoxicity ofidentified phenolics was assessed (repeatedly) through a standard germination bioassay on native Isotoma axillaris. The impact of boneseed litter on native Xerochrysum bracteatumwas evaluated using field soil in a greenhouse. Collectively, we found the highest quantity of phenolic compounds in boneseed litter followed by leaf, root and stem. Quantity variedwith extraction media. The rank of phenolics concentration in boneseed was in the order of ferulic acid > phloridzin > catechin > p-coumaric acid and they inhibited germination of I. axillaris with the rank of ferulic acid > catechin > phloridzin > p-coumaric acid. Synergistic effects were more severe compared to individual phenolics. The litter-mediated soil leachate (collected after15 days) exhibited strong phytotoxicity to I. axillaris despite the level of phenolic compounds in the decomposed leachate being decreased significantly comparedwith their initial level. This suggests the presence of other unidentified allelochemicals that individually or synergistically contributed to the phytotoxicity. Further, the dose responsephytotoxic impacts exhibited by the boneseed litter-mediated soil to native X. bracteatum in a more naturalistic greenhouse experiment might ensure the potential allelopathy of otherchemical compounds in the boneseed invasion. The reduction of leaf relative water content and chlorophyll level in X. bracteatum suggest possible mechanisms underpinning plantgrowth inhibition caused by boneseed litter allelopathy. The presence of a substantial quantity of free proline in the target species also suggests that the plant was in a stressed conditiondue to litter allelopathy. These findings are important for better understanding the invasive potential of boneseed and in devising control strategies. Copyright: