Pest Risk Assessments (PRAs) routinely employ climatic niche models to identify endangered areas. Typically, these models consider only climatic factors, ignoring the ‘Swiss Cheese’ nature of species ranges due to the interplay of climatic and habitat factors. As part of a PRA conducted for the European and Mediterranean Plant Protection Organization, we developed a climatic niche model for Parthenium hysterophorus, explicitly including the effects of irrigation where it was known to be practiced. We then downscaled the climatic risk model using two different methods to identify the suitable habitat types: expert opinion (following the EPPO PRA guidelines) and inferred from the global spatial distribution. The PRA revealed a substantial risk to the EPPO region and Central and Western Africa, highlighting the desirability of avoiding an invasion by P. hysterophorus. We also consider the effects of climate change on the modelled risks. The climate change scenario indicated the risk of substantial further spread of P. hysterophorus in temperate northern hemisphere regions (North America, Europe and the northern Middle East), and also high elevation equatorial regions (Western Brazil, Central Africa, and South East Asia) if minimum temperatures increase substantially. Downscaling the climate model using habitat factors resulted in substantial (approximately 22–53%) reductions in the areas estimated to be endangered. Applying expert assessments as to suitable habitat classes resulted in the greatest reduction in the estimated endangered area, whereas inferring suitable habitats factors from distribution data identified more land use classes and a larger endangered area. Despite some scaling issues with using a globally conformal Land Use Systems dataset, the inferential downscaling method shows promise as a routine addition to the PRA toolkit, as either a direct model component, or simply as a means of better informing an expert assessment of the suitable habitat types.

A triazine-resistant (R) biotype of Phalaris paradoxa L. (hood canarygrass) was superior to a triazine-susceptible (S) biotype in seed-germinability and seedling emergence. It was equal or superior to the S-biotype in growth under noncompetitive conditions. Rates of CO2 uptake by Rplants were similar to those of S-plants, except at very low photon flux densities, where S-plants exhibited higher rates of CO2 uptake. Fluores (25). Triazine resistance has been correlated to reduced binding of herbicides to thylakoids (2), in isolated chloroplasts and in whole plants. PSII mediated electron transport in chloroplasts isolated from R' plants, was virtually unaffected by s-triazines at concentrations that fully inhibit these reactions in chloroplasts from susceptible (S) plants ( 18,24).Resistance to triazines is maternally inherited and due to an alteration in a plastid gene product (23). In addition to triazine resistance, this mutation results in alteration of the electron transport mechanism, which is expressed as reduced quantum yield for whole chain electron transport (3). This reduction in quantum yield usually is cited as a reason for the decrease in photosynthetic potential and overall ecological fitness of triazine resistant weeds (1,6,16,17). When compared to plants of Sbiotypes, R-plants exhibit lower rates of carbon fixation and reduced growth under noncompetitive conditions, as well as reduced ability to compete with the corresponding S-plants. Reduced vigor is regarded as an intrinsic feature of the herbicideresistance phenomenon (7).'Abbreviations: R, triazine resistant; S, triazine susceptible; I, PPFD, photosynthetic photon flux density; Vma,, maximal rate of electron transport or CO2 uptake; K,, photon flux density necessary for half the maximal rate; Qy, quantum yield; 9-AA, 9-aminoacridine. Several R grass weeds were recently discovered in Israel (8,19,27). One of these species, Phalaris paradoxa, is a major weed in cereal crops in the mediteranean area. The results of the present study indicate that the R-biotype of P. paradoxa is not inferior to the S-biotype in photosynthetic potential, or in growth under noncompetitive conditions. This study suggests that triazineresistance is not necessarily linked to reduced plant vigor. Theoretical and practical implications ofthese findings are discussed. MATERIALS AND METHODSPlant Material. Seeds of R Phalaris paradoxa were collected along roadsides in several locations in Israel which have been treated for more than 5 consecutive years with atrazine or simazine. Seeds of the triazine susceptible biotype were collected from nearby cultivated fields which have never been treated with these herbicides. For propagation purposes, plants of the R-and S-biotypes were separately grown in a screenhouse, under the ambient conditions prevailing in the Israeli winter. Seeds harvested from these plants were dry stored in 5°C, and used for all experiments within a year.Seed Germination and Seedling Emergence. Germination of R-and S-seeds was tested on filter ...

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Parthenium or famine weed (Parthenium hysterophorus L.) is an annual plant originating from the Americas, which is a major invasive alien plant in almost all continents. While the deleterious impacts of the species on agriculture, human and animal health have been well documented, information on the pathways of entry of the species is only occasionally mentioned in the literature. As this invasive alien plant is only recorded as established in Israel and Egypt within the Euro-Mediterranean region, the European and Mediterranean Plant Protection Organization identified P. hysterophorus as an emerging threat. EPPO therefore performed a Pest Risk Analysis on this species to assess the risk it represents and to consider appropriate management options. The EPPO Pest Risk Analysis main outputs are summarized in this article, indicating the probability of entry of the species via the different pathways within the EPPO region, its probabilities of establishment and spread, and the magnitude of its potential agricultural, environmental and social impacts.

Parthenium weed (Parthenium hysterophorus L.) (Asteraceae; Heliantheae) is an invasive allergenic species that has invaded many countries worldwide, probably through an imported pasture, grain seeds, and livestock feed. In recent years, there has been increasing concern about the spread of the invasive P. hysterophorus in agricultural and non-agricultural habitats across Israel. In addition, as P. hysterophorus is a quarantine plant; any contaminated produce exported will be rejected by the European market. The current study aims to document the current distribution and invasiveness status of P. hysterophorus in Israel. Moreover, we aimed to study the life cycle and biology of P. hysterophorus. In this research, we detected invasion reports to new areas and habitats in the Jezreel valley, the Jordan valley, and the Mediterranean coastal plain. Studying the biology of the weed, we found that optimal temperatures for seed germination are between 15 and 25°C. We observed that P. hysterophorus seeds are able to emerge from a depth of 0–3 cm only. P. hysterophorus thrives under high light intensities. Our results show that under induced shading of 60 and 90%, a significant reduction in biomass, height, and a number of flowers per plant were observed. Studying the biology and phenology of P. hysterophorus is a crucial step in the path to develop an integrated management program aimed to reduce the further spread and negative impacts by P. hysterophorus.