Abstract
Parthenium weed (Parthenium hysterophorus L.) is an invasive plant species in around 50 countries and a ‘Weed of National Significance’ in Australia. This study investigated the relative toxicity of the leaf, shoot and root extracts of two geographically separate and morphologically distinct biotypes of parthenium weed in Queensland, Australia. Parthenium weed exhibited higher phytotoxic, cytotoxic and photocytotoxic activity in leaf tissue extracts in contrast to shoot and root. The germination and seedling growth of a dicot species (garden cress) were inhibited more than those of a monocot species (annual ryegrass) using a phytotoxicity bioassay. The cytotoxicity of leaf extracts was assessed in a mouse fibroblast cell suspension assay and increased under high ultraviolet A(UV-A) radiation. A major secondary metabolite, parthenin, was found in abundance in leaf extracts and was positively correlated with cytotoxicity but not with photocytotoxicity or phytotoxicity. Ambrosin and chlorogenic acid were also detected and were positively correlated with germination inhibition and the inhibition of radicle elongation, respectively. In addition, other currently unidentified compounds in the leaf extracts were positively correlated with phytotoxicity, cytotoxicity and photocytotoxicity with two to three molecules strongly correlated in each case. Both parthenium weed biotypes investigated did not differ with respect to their relative toxicity, despite their reported differences in invasive potential in the field. This suggests that secondary chemistry plays a limited role in their invasion success.
Highlights
Invasive alien plant species are a global threat to biodiversity, ecosystem function and agricultural productivity [1]
The crude shoot and root extracts of parthenium weed caused no significant inhibition of garden cress seed germination, radicle elongation and hypocotyl elongation at moderate dosages in comparison to the methanol control (Table S1)
Significant inhibition of germination (Figure 1), as well as radicle (Figure 2) and hypocotyl elongation (Figure 3), were noted in both garden cress and annual ryegrass treated with leaf extracts of both biotypes
Summary
Invasive alien plant species are a global threat to biodiversity, ecosystem function and agricultural productivity [1]. Parthenium weed (Parthenium hysterophorus L.) is a highly invasive plant that has invaded 50 countries in Africa, Asia, and Oceania, where it infests forests, grazing lands, crop production systems and urban landscapes [1,2]. It is listed among the world’s most important invasive weeds due to its impacts on the natural and agricultural environment, including the loss of yield and quality in agronomic crops, loss of pasture and livestock productivity, land devaluation, and as the causal agent of serious health problems in mammalian systems [1,3]. Similar negative impacts have been reported from numerous countries in its invasive range [2]
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