Residual phytotoxicity of parthenium: Impact on some winter crops, weeds and soil properties

The Host Range and Risk Assessment of the Stem-Boring Weevil, Listronotus setosipennis (Coleoptera: Curculionidae) Proposed for the Biological Control of Parthenium hysterophorus (Asteraceae) in Pakistan

Parthenium, or Parthenium hysterophorus, has extended its range in Pakistan throughout Punjab and into Khyber Pakhtunkhwa, the Federally Administrated Tribal Areas, Azad Jammu and Kashmir, and Sindh Provinces. Without control measures against parthenium, the negative impacts of this weed will go unchecked having deleterious effects on native biodiversity, human and animal health, as well as crop productivity. The weevil Listronotus setosipennis was obtained and imported from the Plant Health and Protection of the Agricultural Research Council (ARC-PHP), in Cedara, South Africa, in April 2019. A total of 22 plant species or cultivars in the Asteraceae family were assessed during no-choice oviposition tests in Pakistan. During these tests, the only plant species accepted for oviposition were the 10 cultivars of Helianthus annuus that are grown in Pakistan. All cultivars were thus tested for development of L. setosipennis from egg to adult. Only three cultivars were able to support some larval development, but at such low levels that it is unlikely to be the basis of a viable population. To support this, a risk assessment was conducted to ascertain the probability of L. setosipennis being able to sustain viable populations in the field, the results of which concur with native (Argentina) and introduced (Australia) field host-range information where L. setosipennis has never been recorded as a pest of sunflowers. The results of laboratory-based host-range trials, together with host records from its native and introduced range, indicate that L. setosipennis is sufficiently specific to parthenium and is thus suitable for release in Pakistan.

Impact of Parthenium hysterophorus L. invasion on soil nitrogen dynamics of grassland vegetation of Indo-Gangetic plains, India

The noxious plant species Parthenium hysterophorus L. has become a major concern for the conservation of many natural and managed areas. The species is known for its various adverse effects on the invaded ecosystems, particularly in terms of biodiversity loss. Currently, P. hysterophorus is a leading invasive species widespread in the grasslands of productive and diversity rich Indo-Gangetic plains of India and is responsible for various changes in the ecosystem. The present study addresses the changes that P. hysterophorus can bring in the vegetation structure (species richness, species evenness, and species composition) of the grasslands of Indo-Gangetic plain. To broaden our understanding of the invasion success and facilitated expansion, we also focus on the variability of soil nitrogen pool and processes as a consequence of invasion. We report that in the presence of P. hysterophorus, the species diversity, evenness, composition and richness were altered, affecting many native and non-native flora of the ecosystem. The effect was more prominent during the second and third year of the study with more increase in the invasion outcomes. Significant changes in soil nitrogen (N) dynamics, particularly, increased available (N), N-mineralization and microbial biomass N have been found in the invaded plots along with changes in vegetation of the grassland community. Overall, the result suggested that the invasive species, P. hysterophorus, modifies the soil and this modification is correlated with changes in vegetation structure and this situation is likely to further facilitate severe alterations in the ecosystem and could favor encroachment of other non-native species in the area.

Parthenium hysterophorus: A tale of global invasion over two centuries, spread and prevention measures

Ever since parthenium weed (Parthenium hysterophorus L.) first left its native range more than two centuries ago, this noxious herb has now invaded 46 countries and territories. The weed has expanded its range from a couple of islands in 18th Century through 11 minor and eight major introductions around the world. Segmented regression analyses confirmed introductions and revealed that the weed has spread fastest in developing countries, especially after the 1950s in Asia and Africa. A review of historical records, research papers and reports suggests that while border traffic (36%) and unchecked imports (seeds 16%, other commodities 17%) have resulted in the majority of international introductions, local spread has been achieved through multiple pathways, including roads and vehicles, by water and wind, through contaminated seed feed lots and floral bouquets. The high proportion of adjacent counties (51%) and oversea islands (5%) over the unknown origins (32%) or directly from the native range (12%) reveal a steady and predictable international spread pattern. Prevention of spread by management was first practised in Australia, then followed by other five countries. Containment barriers were set up, legislation on biosecurity imposed, and management plans based on early detection and eradication were executed; and these measures have been effective. Awareness within international research groups is raising, however, insufficient coordination between invaded countries has occurred to date, with policies yet to be formalised and executed to prevent the spread and impact of this weed.

Toxic Potential and Metabolic Profiling of Two Australian Biotypes of the Invasive Plant Parthenium Weed (Parthenium hysterophorus L.)

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.