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Invasive species offer outstanding opportunities to identify the genomic sources of variation that contribute to rapid adaptation, as well as the genetic mechanisms facilitating invasions. The Eurasian plant yellow starthistle (Centaurea solstitialis) is highly invasive in North and South American grasslands and known to have evolved increased growth and reproduction during invasion. Here, we develop new genomic resources for C. solstitialis and map the genetic basis of invasiveness traits. We present a chromosome-scale (1N = 8) reference genome using PacBio CLR and Dovetail Omni-C technologies, and functional gene annotation using RNAseq. We find repeat structure typical of the family Asteraceae, with over 25% of gene content derived from ancestral whole-genome duplications (paleologs). Using an F2 mapping population derived from a cross between native and invading parents, with a restriction site-associated DNA (RAD)-based genetic map, we validate the assembly and identify 13 quantitative trait loci underpinning size traits that have evolved during invasion. We find evidence that large effects of quantitative trait loci may be associated with structural variants between native and invading genotypes, including a variant with an overdominant and pleiotropic effect on key invader traits. We also find evidence of significant paleolog enrichment under two quantitative trait loci. Our results add to growing evidence of the importance of structural variants in evolution, and to understanding of the rapid evolution of invaders. [ABSTRACT FROM AUTHOR]

It is increasingly recognized that different genetic variants of hosts can uniquely shape their microbiomes. Invasive species often evolve in their introduced ranges, but little is known about the potential for their microbial associations to change during invasion as a result. We asked whether host genotype (G), microbial environment (E), or their interaction (G × E) affected the composition and diversity of host-associated microbiomes in Centaurea solstitialis (yellow starthistle), a Eurasian plant that is known to have evolved novel genotypes and phenotypes and to have altered microbial interactions, in its severe invasion of CA, USA. We conducted an experiment in which native and invading plant genotypes were inoculated with native and invaded range soil microbial communities. We used amplicon sequencing to characterize rhizosphere bacteria in both the experiment and the field soils from which they were derived. We found that native and invading plant genotypes accumulated different microbial associations at the family level in each soil community, often counter to differences in family abundance between soil communities. Root associations with potentially beneficial Streptomycetaceae were particularly interesting, as these were more abundant in the invaded range field soil and accumulated on invading genotypes. We also found that bacterial diversity is higher in invaded soils, but that invading genotypes accumulated a lower diversity of bacteria and unique microbial composition in experimental inoculations, relative to native genotypes. Thus variation in microbial associations of invaders was driven by the interaction of plant G and microbial E, and rhizosphere microbial communities appear to change in composition in response to host evolution during invasion. [ABSTRACT FROM AUTHOR]

IntroductionInvasive alien plants (IAPs) are major hazards to biodiversity, human health, and the agricultural economy. As one of the most aggressive species of IAPs, the distribution area of Centaurea solstitialis L. has increased exponentially in the past two years since its invasion into Xinjiang, China, in July 2014. Predicting the potential geographic distributions (PGDs) of C. solstitialis in China can provide theoretical support for preventing the continued spread of this weed.MethodsIn this study, based on 5,969 valid occurrence records of C. solstitialis and 33 environmental variables, we constructed an ensemble model to predict suitable habitats for C. solstitialis under climate change scenarios.ResultsOur results showed that the mean true skill statistic (TSS) values, area under the receiver operating characteristic (ROC) curve (AUC), and Cohen’s Kappa (KAPPA) for the ensemble model were 0.954, 0.996, and 0.943, respectively. The ensemble model yielded more precise predictions than those of the single model. Temperature seasonality (Bio4), minimum temperature of the coldest month (Bio6), precipitation of the driest month (Bio14), and human influence index (HII) have significantly disrupted the PGDs of C. solstitialis in China. The total (high) suitability habitat area of C. solstitialis in China was 275.91 × 104 (67.78 × 104) km2, accounting for 71.26 (7.06)% of China. The PGDs of C. solstitialis in China under the current climate were mainly in East China (Shandong, Jiangsu, Shanghai, Zhejiang, and Anhui), Central China (Henan, southwestern Shanxi, southern Shaanxi, southern Gansu, Hubei, Hunan, Jiangxi, Chongqing, and Guizhou), and South China (southern Tibet, eastern Sichuan, Yunnan, Guangxi, Guangdong, Fujian, and Taiwan). Under future climate scenarios, the total suitability habitat area for C. solstitialis will expand, whereas the high suitability habitat area will decrease.DiscussionThe main manifestation is that the shift of southeast China into a moderate suitability habitat, and the total suitability habitats will be extended to northwest China. More focus needs to be placed on preventing further spread of C. solstitialis in northwest China.

The Mentha pulegium, Lepidiıum draba and Centaurea solstitialis have traditionally been used in different cultures for the treatment of various diseases. We investigated the total phenolic content analysis, chemical compositions and antioxidant activities of different solvent extracts such as acetone, methanol and n-hexane obtained from the aerial parts of Mentha pulegium, Lepidiıum draba and Centaurea. The amount of total phenolic substance was determined as gallic acid equivalent determine. Also, the LC-MS/MS technique was used to determine the phenolic profiles of each extract. Finally, antioxidant activities of three extracts were determined by DPPH and ABTS methods. The highest total phenolic content for acetone, n-hexane and methanol extracts was found as 99 507, 46 305, and 18 227 µg GAE mL-1 in Centaurea solstitialis plant, respectively. While the major component rosmarinic acid amount in the acetone extract of Mentha pulegium was 128 195 µg analyte g-1 extract, this amount was determined as 780 383 µg analyte g-1 extract in the methanolic extract. The highest DPPH radical scavenging activity was found in the acetone and methanolic extracts of Mentha pulegium as 77% and 79%, respectively. ABTS radical scavenging activity was also found to be 98% and 94% for Mentha pulegium in acetone and methanol extracts, respectively. The antioxidant capacity of the extracts is related to the total amount of phenolic substances. [ABSTRACT FROM AUTHOR]

The evolution of increased competitive ability (EICA) hypothesis encapsulates the importance of evolution and ecology for biological invasions. According to this proposition, leaving specialist herbivores at home frees introduced plant species from investing limited resources in defense to instead use those resources for growth, selecting for individuals with reduced defense, enhanced growth, and, consequently, increased competitive ability. We took a multispecies approach, including ancestral and non‐native populations of seven weeds, as well as seven coexisting local weeds, to explore all three predictions (i.e., lower defense, greater growth, and better ability to compete in non‐native than ancestral populations), the generality as an invasion mechanism for a given system, and community‐level consequences of EICA. We assessed plant defenses by conducting herbivory trials with a generalist herbivore. Therefore, finding that non‐native populations are better defended than ancestral populations would lend support to the shifting defense (SD) hypothesis, an extension of EICA that incorporates the observation that introduced species escape specialists, but encounter generalists. We also manipulated water additions to evaluate how resource availability influences competition in the context of EICA and plant plasticity in our semiarid system. We found that non‐native populations of one study species, Centaurea solstitialis, were better defended, grew faster, and exerted stronger suppression on locals than ancestral populations, offering support to EICA through the SD hypothesis. The other species also displayed variation in trait attributes between ancestral and non‐native populations, but they did not fully comply with the three predictions of EICA. Notably, differences between those populations generally favored the non‐natives. Moreover, non‐native populations were, overall, superior at suppressing locals relative to ancestral populations under low water conditions. There were no differences in plasticity among all three groups. These results suggest that evolutionary change between ancestral and non‐native populations is widespread and could have facilitated invasion in our system. Additionally, although trading growth for shifted defense does not seem to be the main operational path for evolutionary change, it may explain the dominance of some introduced species in ruderal communities. Because introduced species dominate communities in disturbed environments around the world, our results are likely generalizable to other systems. [ABSTRACT FROM AUTHOR]

Premise: Trait variation, trade‐offs, and attributes can facilitate colonization and range expansion. We explored how those trait features compare between ancestral and nonnative populations of the globally distributed weed Centaurea solstitialis. Methods: We measured traits related to survival, size, reproduction, and dispersal in field sampling following major environmental gradients; that of elevation in Anatolia (ancestral range) and that of precipitation in Argentina (nonnative range). We also estimated abundance. Results: We found that overall variation in traits in ancestral populations was similar to that in nonnative populations. Only one trait—seed mass—displayed greater variation in ancestral than nonnative populations; coincidentally, seed mass has been shown to track global range expansion of C. solstitialis. Traits displayed several associations, among which seed mass and number were positively related in both ranges. Many traits varied with elevation in the ancestral range, whereas none varied with precipitation in the nonnative one. Interestingly, most traits varying with elevation within the ancestral range also displayed differences in attributes between ancestral and nonnative ranges. Unexpectedly, ancestral plants were more fecund than nonnative plants, but density was greater in the nonnative than ancestral range, indicating that C. solstitialis survives at larger proportions in the nonnative than ancestral range. Conclusions: Our results suggest that maintaining levels of trait variation in nonnative populations comparable to those in ancestral populations, avoiding trait trade‐offs, and developing differences in trait attributes between ranges can play a major role in the success of many weeds in novel environments. [ABSTRACT FROM AUTHOR]

HIGHLIGHTS The phenolic composition, antioxidant activity and cytotoxic potential of the extracts of C. solstitialis and U. picroides were investigated. Caffeic acid was found as the most abundant phenolic compound in the extracts. Both species showed promising antioxidant activity towards different assays. The highest cytotoxic potential was observed in the extract of C. solstitialis.

Adsorption is one of the most widely used methods for dye removal from water. At the end of the adsorption process, the dyed adsorbents emerging as a second-order waste which is the main disadvantage of this process. In this study, the removal of a synthetic dye Crystal Violet (CV) from the synthetic wastewater by using Centaurea solstitialis (CS) and Verbascum Thapsus (VT) plants was studied by adsorption. At the end of the adsorption process, the reusing potential of the dyed plant was explored by measuring the dyed plant calorific values. Experimental design and modeling were performed using the surface response method (RSM). The regression coefficients for developed models were 0.86 for the CS plant and 0.95 for the VT plant. Adsorption process for CS and VT plants were fitted by Dubinin-Radushkevich isotherm, and Temkin isotherm, respectively. The two plants were pseudo-second-order, endothermic, and found to be chemically. CS plant had a capacity of 84.03 mg.g-1 with a contact time of 85 min. The capacity of the VT plant reached 109.89 mg.g-1 at a contact time of 55 min. The calorific values results show increases in the calorific values for the two plants after the adsorption process. The CS plant increased from 4003.774 to 4458.059 Kcal.Kg-1. Whereas the VT plant increased from 3206.028 to 4120.330 Kcal.Kg-¹. These values indicate the using possibility of the two plants as solid fuel by burning the dyed plants in emission controlled industrial facilities by applying the zero-waste concept. [ABSTRACT FROM AUTHOR]

At two field sites that differed in fertility, we investigated how species richness, functional group diversity, and species composition of constructed plant communities influenced invasion. Grassland communities were constructed to be either functionally diverse or functionally simple based on belowground resource use patterns of constituent species. Communities were also constructed with different numbers of species (two or five) to examine interactions between species richness, functional diversity and invasion resistance. We hypothesized that communities with more complementary belowground resource use (i.e., more species rich and more functionally diverse communities) would be less easily invaded than communities with greater degrees of belowground resource use overlap. Two contrasting invasive species were introduced: an early-season, shallow rooting annual grass, Bromus hordeaceus (soft chess), and a late-season, deep rooting annual forb, Centaurea solstitialis (yellow starthistle). Invader responses to species richness and functional diversity treatments differed between sites. In general, the more similar the patterns of belowground resource use between residents of the plant community and the invader, the poorer the invader’s performance. Complementarity or overlap of resource use among species in the constructed communities appeared to affect invader success less than complementarity or overlap of resource use between the invader and the species present in the community.

With increasing ecological awareness, researchers around the world seek to make composites reinforced with more eco-friendly natural fibers. In this study, Centaurea solstitialis (yellow star thistle) fibers were characterized as a potential natural fiber reinforcement for green composites. Generally, Centaurea solstitialis plants are undesirable because of their detrimental effect on other plants. In this respect, they are generally considered economically worthless in terms of the economical aspect. From this point of view, characterizing Centaurea solstitialis and using them as a natural fiber reinforcement material can be more appropriate in terms of waste management. To characterize the Centaurea solstitialis fibers, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, X-ray Photoelectron Spectroscopy, X-Ray Diffraction Analysis, single fiber tensile test, determinations of density and chemical composition were performed. Centaurea solstitialis fibers have 11.2% hemicellulose and 57.20% cellulose content. The crystallinity index and density of fibers were determined as 71.43% and 1.37 g/cm3, respectively. Also, fibers exhibited relatively high tensile strength with 111.85 ± 24.97 MPa and Young's modulus with 3.41 ± 0.62 GPa. The thermal resistance temperature of Centaurea solstitialis fibers was found as 273 °C. It is suggested that Centaurea solstitialis fiber is a suitable reinforcement candidate for composites with low density, low cost, abundancy and relatively high tensile strength. [ABSTRACT FROM AUTHOR]

Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C.solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C.solstitialis. From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m2 plots in C.solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C.solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall. [ABSTRACT FROM AUTHOR]

The effects of many invasive species on invaded communities are still scarcely known. Centaurea solstitialis is an invasive Eurasian herb, widely distributed around the world, but its effects on recipient communities are not well known. To evaluate the effect of C. solstitialis invasion on richness and cover of native and exotic resident species in naturally established communities. We repeated a field experiment in three old-fields of central Chile where C. solstitialis was not present. The experiment simulated the invasion of C. solstitialis by adding 600 seeds per plots of 1 × 1 m in size and compared the richness and cover of all naturally growing species in plots with and without C. solstitialis. For exotics, initial species richness (average ca.18% and 20% per site), and cover (average ca. 20% and 34% per site) were significantly reduced by C. solstitialis in two out of the three sites. The abundances of four out of 17 exotic resident species were negatively affected by C. solstitialis. Native species were not affected by C. solstitialis. C. solstitialis can outcompete resident species of communities where it invades, but local ecological factors influence its effects producing different impacts among species and localities. [ABSTRACT FROM AUTHOR]

Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

Centaurea solstitialis es una planta con propiedades antiulcerosas. Teniendo como objetivo lograr el aislamiento, identificación y cuantificación de compuestos bioactivos responsables de la actividad gastroprotectora, se llevaron a cabo estudios fitoquímicos bioguiados en busca de flavonoides relacionados con esta actividad farmacológica. Una fracción metanólica obtenida a partir de capítulos desecados de la planta, fue extraída con acetato de etilo previa hidrólisis con ácido clorhídrico. La fracción acetato de etilo fue cromatografiada en capa delgada sobre placas de sílica gel y las bandas, que comigraron con estándares auténticos de quercetina (Rf = 0,80) y canferol (Rf = 0,89), se purificaron por HPLC, obteniéndose el aislamiento de los dos flavonoides. Los compuestos fueron recuperados e identificados por espectrometría de masas. Ensayos cuantitativos permitieron determinar que los capítulos de la planta contienen 0,63 y 1,47 mg de quercetina y canferol por gramo de materia seca respectivamente

Residuos de extractos acuosos, metanólicos y clorofórmicos de flores de Centaurea solstitialis L. Compositae, comúnmente llamada Abrepuño, fueron resuspendidos con una mezcla de excipientes, Tween 80 (T80) y Carboximetilcelulosa (CMC) y administrados por medio de sonda gástrica a ratas Wistar hembras con e1 objeto de estudiar las propiedades citoprotectoras de la planta sobre las úlceras provocadas por estrés por inmersión en agua. El ensayo se llevó a cabo administrando a un grupo de cinco ratas T80 + CMC como testigo. Otros cuatro grupos, de igual número de animales, fueron tratados con residuos acuoso( a), metanólico (b), metanólico-clorofórmico( 1:1) (c) y clorofórmico (d), todos ellos resuspendidose n una mezclad e T80 + CMC. En los grupos a, c y dla prevención de úlceras fue de un 1000/om, ientras que en el grupo b se logró un78o6 (p 0,05). Los extractos metanólicos y cloroformicos, que contienen flavonoides y sesquiterpenol actonas respectivamente,serían los responsables de los efectos citoprotectores evidenciados por estos resultados

Abstract The role of plant diversity in reducing invasions has generated decades of debate. Diverse communities might be more resistant to invasion because the communities contain resident species that are functionally similar to the invader (limiting similarity), or multiple species use the range of available resources more effectively (complementarity) than single species. However, the correlation of native and exotic diversity often reverses, becoming positive, with increasing spatial and temporal scale, in a phenomenon called the invasion paradox. We addressed two groups of hypotheses related to this paradox, broadly that (1) functional diversity and identity resist invasion initially, via complementarity or limiting similarity; and (2) disturbance and propagule pressure weaken the effects of functional diversity and identity on invader success through time. Using long‐term data from experimental serpentine grassland assemblages in California, we examined how the abundance of a high impact invader, yellow starthistle (Centaurea solstitialis), related to functional diversity, functional dissimilarity, pocket gopher disturbance, and propagule pressure. We also conducted a single‐season experiment in which we seeded disturbed and undisturbed areas and quantified invader success the following year. Neither diversity, nor dissimilarity, nor disturbance significantly impacted the success of C. solstitialis during the years of this study. Instead, propagule pressure was the single most important predictor of C. solstitialis abundance. We consolidated these findings into a novel conceptual model of invader success to illustrate how propagule input may outweigh community resistance through time, and what implications these dynamics have for the invasion paradox.

Objectives: Natural products originating from plants have been used for many years in the treatment of various diseases, including cancer. Centaurea solstitialis subsp. solstitialis is used in Turkish folk medicine. This study was the first to determine the in vitro biological effects of ethanolic extract from the flowering parts of C. solstitialis L. subsp. solstitialis collected from Mugla Province. Materials and Methods: The cytotoxic effect was evaluated against Daudi, A549, and HeLa cancer cells and one normal BEAS-2B cell line using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5- dipenyltetrazolium bromide) assay. Flow cytometric analysis and the caspase-3 activity assay were performed to detect apoptotic cell death. Angiogenic factor [vascular endothelial growth factor (VEGF)] secretion and the release of interleukin (IL)-1a, IL-6, and tumor necrosis factor (TNF)-a by cells treated with the extract were measured using enzyme-linked immunosorbent assay. Results: The extract exhibited cytotoxic effects against all the cancer cell lines used but HeLa and Daudi were the most sensitive cells, with IC50 values of 63.18 µg/mL and 69.27 µg/mL, respectively. Selective cytotoxicity was observed between the HeLa and normal BEAS-2B cell lines. The extract arrested the cell cycle at the S and G2 phases. In addition, apoptotic cell death was detected in HeLa and A549 cells. Moreover, the plant extract caused a significant decrease in VEGF secretion in A549 cells and a fluctuation in IL-1a, IL-6, and TNF-a secretion in A549 and Daudi cells. Conclusion: These observations suggest that the flowering parts of C. solstitialis may be a potential source in the development of natural drugs for the treatment of cancer and modulation of cytokine secretion. [ABSTRACT FROM AUTHOR]

The role of plant diversity in reducing invasions has generated decades of debate. Diverse communities might be more resistant to invasion because the communities contain resident species that are functionally similar to the invader (limiting similarity), or multiple species use the range of available resources more effectively (complementarity) than single species. However, the correlation of native and exotic diversity often reverses, becoming positive, with increasing spatial and temporal scale, in a phenomenon called the invasion paradox. We addressed two groups of hypotheses related to this paradox, broadly that (1) functional diversity and identity resist invasion initially, via complementarity or limiting similarity; and (2) disturbance and propagule pressure weaken the effects of functional diversity and identity on invader success through time. Using long-term data from experimental serpentine grassland assemblages in California, we examined how the abundance of a high impact invader, yellow starthistle (Centaurea solstitialis), related to functional diversity, functional dissimilarity, pocket gopher disturbance, and propagule pressure. We also conducted a single-season experiment in which we seeded disturbed and undisturbed areas and quantified invader success the following year. Neither diversity, nor dissimilarity, nor disturbance significantly impacted the success of C. solstitialis during the years of this study. Instead, propagule pressurewas the singlemost important predictor of C. solstitialis abundance. We consolidated these findings into a novel conceptual model of invader success to illustrate how propagule input may outweigh community resistance through time, andwhat implications these dynamics have for the invasion paradox. [ABSTRACT FROM AUTHOR]

• E. villosus and L. curtus infestation levels differ among macroclimate regions. • E. villosus and L. curtus seed consumption differ among macroclimate regions. • Winter conditions of a continental climate influence L. curtus and E. villosus. A 2-year field study (2014–2015) was conducted to determine the levels of Eustenopus villosus (Boheman) and Larinus curtus (Hochhut) infestation and seed consumption of the invasive plant Centaurea solstitialis L. (Asteraceae: Cardueae) in the steppe of southeastern Washington, USA, a marine-modified continental macroclimate. Mature terminal C. solstitialis flowerheads were collected and dissected to determine abundance of each weevil species and level of seed consumption by both species. Data were analyzed by year to assess climatic influences on insect prevalence and feeding activity. Results showed that E. villosus infested 34.2% of the flowerheads in 2014 and 29.9% in 2015. Larinus curtus infested 10.9% in 2014 and 13.7% in 2015. In 2014, 5.8% of the flowerheads were infested by at least one E. villosus and one L. curtus in the same flowerhead and 9.7% in 2015. Eustenopus villosus consumed a higher percentage of total seed production per flowerhead of C. solstitialis than L. curtus (71.4% and 59.8, respectively). Infestation levels of E. villosus and L. curtus in southeastern Washington are lower than in the Mediterranean macroclimates in California and northern Greece. Mean seed consumption was also lower in southeastern Washington compared to northern Greece, with no data specific to California. Lower levels of infestation and seed consumption in southeastern Washington suggests the efficacy of the insect biological controls may be less in more continental macroclimates than in climates with Mediterranean influences. [ABSTRACT FROM AUTHOR]

The margins of an expanding range are predicted to be challenging environments for adaptation. Marginal populations should often experience low effective population sizes (Ne) where genetic drift is high due to demographic expansion and/or census population size is low due to unfavourable environmental conditions. Nevertheless, invasive species demonstrate increasing evidence of rapid evolution and potential adaptation to novel environments encountered during colonization, calling into question whether significant reductions in Ne are realized during range expansions in nature. Here we report one of the first empirical tests of the joint effects of expansion dynamics and environment on effective population size variation during invasive range expansion. We estimate contemporary values of Ne using rates of linkage disequilibrium among genome‐wide markers within introduced populations of the highly invasive plant Centaurea solstitialis (yellow starthistle) in North America (California, USA), and within native Eurasian populations. As predicted, we find that Ne within the invaded range is positively correlated with both expansion history (time since founding) and habitat quality (abiotic climate). History and climate had independent additive effects with similar effect sizes, indicating an important role for both factors in this invasion. These results support theoretical expectations for the population genetics of range expansion, though whether these processes can ultimately arrest the spread of an invasive species remains an unanswered question. [ABSTRACT FROM AUTHOR]

Congeneric species with the same native and non-native ranges, but exhibiting different invasiveness, provide opportunities to assess the relative importance of factors contributing to successful invasions. For example, comparing the competitive ability of such congeners against other species from the native and non-native regions of invasive species can provide insight into the role of evolutionary experience with different competitors. We selected two congeneric Centaurea species with overlapping native and non-native ranges but with strikingly different invasive success, Centaurea solstitialis and C. calcitrapa, and conducted experiments with populations from each region using a suite of different native grass species from each region. When grown with Spanish grass species, competitive responses were 32% stronger for C. calcitrapa and 30% stronger for C. solstitialis, than when in competition with grasses native to California. Centaurea solstitialis from California had 66% higher competitive effects on grasses, all species considered together, than Spanish C. solstitialis; whereas the competitive effects of C. calcitrapa on grasses were not significantly different between C. calcitrapa ranges. Our results are consistent with the prediction that the evolution of increased competitive ability (EICA) might contribute to the devastating success of C. solstitialis in California, and that its absence might contribute to the modest naturalization of the non-invasive C. calcitrapa. Escape from the strong competitive effects and responses of grasses from Spain may also contribute to invasive success in California. Our results suggest that studies of EICA should be based on competitive tests, since biomass alone is not always a good predictor of competitive ability. [ABSTRACT FROM AUTHOR]

Abstract: Many plant invasion studies in grasslands suggest that resident plants that share functional traits with invaders can reduce invasion by competing for limiting resources. However, since invasion studies often occur in highly controlled plots or microcosms, it is unclear how heterogeneous site conditions alter competitive interactions under realistic scenarios. To explore how landscape heterogeneity affects biotic resistance provided by competitive resident plants, we conducted a field‐based experiment across four sites in California grasslands. Plots contained naturally occurring populations of native Hemizonia congesta, but differed in other characteristics, including litter cover, annual grass cover, soil moisture, and species richness. We invaded plots with the functionally similar nonnative Centaurea solstitalis (yellow starthistle) and, at one site, supplemented one‐half of the established plots with water to test the effects of increasing a limiting resource. As in simplified plots and microcosms, increasing H. congesta abundance reduced starthistle biomass by competing for limited soil moisture, but only in plots with high starthistle germination. We conclude that higher abundances of native H. congesta can reduce starthistle invasion in heterogeneous grasslands, but competition is also affected by both abiotic (soil moisture) and biotic (starthistle germination number) conditions that vary across sites. [ABSTRACT FROM AUTHOR]

The historical management of agroecological systems, such as California's rangelands, have received criticism for a singular focus on agricultural production goals, while society has shifting expectations to the supply of multiple ecosystem services from these working landscapes. The sustainability and the multiple benefits derived from these complex social-ecological systems is increasingly threatened by weed invasion, extreme disturbance, urban development, and the impacts of a rapidly changing and increasingly variable climate. California's grasslands, oak savannas, and oak woodlands are among the most invaded ecosystems in the world. Weed eradication efforts are rarely combined with seeding on these landscapes despite support for the inclusion of the practice in a weed management program. Depending on seed mix choice, cost and long-term uncertainty, especially for native seed, is an impediment to adoption by land managers. We investigated four seeding mixes (forage annual, native perennial, exotic perennial, and exotic-native perennial) to evaluate how these treatments resist reinvasion and support the delivery of simultaneous multiple ecosystem services (invasion resistance, native richness, nitrogen fixing plants, pollinator food sources, plant community diversity, forage quality, and productivity). We found the increase of exotic and native perennial cover will drive resistance to an invading weedy summer flowering forb Centaurea solstitialis but provides a mixed response to resisting invasive annual grasses. The resistance to invasion is coupled with little tradeoff in forage productivity and quality and gains in plant diversity and native cover. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Seed-level trade-off s of heterocarpic species remain poorly understood. We propose that seedlings emerging from seeds with a permanent pappus (dispersing seeds) are stronger competitors than those emerging from seeds without a pappus (nondispersing seeds) because dispersing seeds are larger and germinate faster than nondispersing seeds in Centaurea solstitialis . METHODS: We conducted a competition experiment with both seed morphs, in which we recorded emergence rate and proportion, estimated seed dispersal by wind (anemochory) and by mammals (exozoochory), and measured size and abundance of seed morphs. KEY RESULTS: We found that seedlings from pappus seeds had greater competitive abilities than those from non-pappus seeds. Similarly, pappus seedlings emerged at much faster rates and larger proportions than non-pappus seedlings. Pappus seeds were larger, were more numerous, and displayed improved exozoochory compared to non-pappus seeds. Anemochory was poor for both seed morphs. CONCLUSIONS: We found support for our hypothesis, raising in turn the possibility that competition and colonization are positively associated in seed morphs of heterocarpic species with enhanced exozoochory of larger seeds. These findings are not consistent with those from heterocarpic species with enhanced anemochory of smaller seeds or slower-germinating seeds. Our results additionally suggest that pappus and non-pappus seeds of C. solstitialis display a task-division strategy in which pappus morphs colonize and preempt unoccupied sites through improved dispersal and fast and large emergence of seedlings with increased competitive abilities, whereas non-pappus morphs promote site persistence through delayed germination and dormancy. This strategy may contribute to the success of C. solstitialis in highly variable environments. [ABSTRACT FROM AUTHOR]

A 2-yr (2014-2015) field study in eastern Washington State quantified the effect of environmental factors on the overwintered Eustenopus villosus (Boheman) and Larinus curtus (Hochhut) adults in relation to phenology of Centaurea solstitialis L. (Asteraceae: Cardueae), the feeding and breeding host for these two weevil biocontrol agents. We recorded in the study area: ambient and soil temperatures, soil moisture, percent cover and developmental stage of C. solstitialis, and presence of adults of each weevil species. Sampling took place from early May to mid-August. Weevil activity for both species in both years was segregated into three phases: 1 - a pre-appearance phase in which neither species was detected, 2 - appearance and increase in frequency, and 3 - decrease in frequency. Eustenopus villosus increase in frequency was most strongly associated with warming temperatures both years. Larinus curtus increase in frequency in 2014 was most associated with increasing C. solstitialis cover and in 2015 with warming temperatures and drying soils. In both years, both weevil species' decline in frequency was likely due to the advancing C. solstitialis phenology. This pattern indicates that the appearance and increase in frequency of the overwintered E. villosus and L. curtus adults was likely a function of warming temperatures. Both species' decline in frequency was likely a function of the weevils completing their life cycle in synchrony with the phenological advancement of C. solstitialis and decline of abundant breeding and foraging sites (buds and flowers). [ABSTRACT FROM AUTHOR]

Successful colonization by invasive species depends on both the ability to disperse seeds to a site and an ability to establish once seeds have arrived. While seed and establishment limitation are known to jointly influence colonization, decomposing establishment limitation into density-dependent and density-independent components has remained challenging., Here, we couple theoretical models of recruitment with a multispecies invasion experiment conducted within a natural gradient of soil moisture and productivity to assess how variation in establishment limitation shapes outcomes for invasion., Recruitment was affected by both density-dependent and density-independent sources of establishment limitation in three of four species. Soil moisture stress and productivity both increased density-independent mortality in one species, whereas density-dependent mortality increased in locations with favourable soil moisture., Synthesis. Successful establishment of invading species can be limited by both density-dependent and density-independent mechanisms. In particular, the strength of density-independent limitation may depend on natural gradients in abiotic factors. The varying strengths of establishment limitation suggest that patterns of invasion are likely to be uneven both in space and in time. Understanding how intraspecific competitive constraints and density-independent limitation vary with abiotic gradients can assist with predicting when invasions are likely to occur, information that can be harnessed in the development of better methods for control. [ABSTRACT FROM AUTHOR]

La alteración antrópica del hábitat da paso a la cohabitación de especies importadas que nunca coexistirían en su ámbito natural. Centaurea solstitialis y Centaurea moncktonii son dos especies invasoras cuyas distribuciones en Eurasia apenas se solapan. Después de su introducción en Norteamérica, la expansión invasiva condujo a distribuciones superpuestas. Aunque los requerimientos ambientales de las dos especies son distintos, la proximidad de hábitats diversos (dentro del alcance de los polinizadores) ha dado lugar a varios casos de hibridación natural entre ambas. El cruce resultante entre dos especies lejanamente emparentadas es una planta perenne estéril. Muchos de los caracteres del híbrido son intermedios entre sus especies parentales, pero morfológicamente es más parecida a Centaurea moncktonii (probablemente la especie materna y a su vez ya de origen híbrido). La nueva especie podría convertirse en una mala hierba invasora gracias a su reproducción vegetativa. La que suponemos especie materna, a la cual el híbrido se acerca morfológicamente y puede que fisiológicamente, es una mala hierba rastrera bien conocida de las praderas alpinas en toda Europa. [ct] L’alteració antròpica de l’hàbitat dóna pas a la cohabitació d’espècies importades que mai coexistirien en el seu àmbit natural. Centaurea solstitialis i Centaurea moncktonii són dues espècies invasores les distribucions de les quals a Euràsia gairebé no se solapen. Després de la seva introducció a Amèrica del Nord, l’expansió invasiva va portar a distribucions superposades. Malgrat que els requeriments ambientals de les dues espècies són diferents, la proximitat d’hàbitats diversos (dins de l’abast dels pol·linitzadors) ha donat lloc a diversos casos d’hibridació natural entre ambdues. L’ encreuament resultant entre dues espècies, llunyanament emparentades, és una planta perenne estèril. Molts dels caràcters de l’híbrid són intermitjos entre les seves espècies parentals, però morfològicament és més semblant a Centaurea moncktonii (probablement l’espècie materna, i al seu torn també d’origen híbrid). La nova espècie podria convertir-se en una mala herba invasora gràcies a la seva reproducció vegetativa. La que suposem espècie materna, a la qual l’híbrid s’acosta morfològicament i potser fisiològicament, és una mala herba prostrada ben coneguda de les pastures alpines a tota Europa.

Most remote sensing approaches for mapping invasive plant species focus on species in a prominent phenological stage, such as during flowering, and do not systematically evaluate the performance for mapping lower cover fractions. In this study, we used airborne imaging spectroscopy (also known as hyperspectral imaging) to detect the invasive grass Phalaris aquatica and the invasive herb Centaurea solstitialis in a pre-flowering stage in the Jasper Ridge Biological Preserve, California, and compared the performance of three different one-class classifiers: Maxent, biased support vector machines and boosted regression trees. We collected presence data for C. solstitialis and P. aquatica to calibrate each approach and additional presence-absence data to validate model performance on 3 m × 3 m plots. The imaging spectroscopy data were acquired using the Carnegie Airborne Observatory Visible-to-Shortwave Infrared (VSWIR) imaging spectrometer (400–2500 nm range) with a pixel size of 1 m × 1 m. The resulting overall accuracies were 72–74% for C. solstitialis , and 83–88% for P. aquatica . For both species, the overall performance was slightly better for Maxent and BRT than for biased SVM. The detection rates for low cover plots were considerably higher for C. solstitialis than for P. aquatica . The models relied on different areas of the reflectance spectrum, but still produced the same general pattern of predicted species occurrences. We conclude that the different one-class classifiers allow for the detection and monitoring of target species with similar success rates. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal ( AM) fungi can exert a powerful influence on the outcome of plant-plant competition. Since some exotic plants interact differently with soil biota such as AM fungi in their new range, range-based shifts in AM responsiveness could shift competitive interactions between exotic and resident plants, although this remains poorly studied., We explored whether genotypes of the annual exotic Centaurea solstitialis (yellow starthistle), collected from populations across the native and non-native ranges, differed in responsiveness to AM fungi in the introduced range and whether range-based differences in mycorrhizal responsiveness affected how strongly C. solstitialis tolerated competition with the North American native bunchgrass, Stipa pulchra., Grown alone, C. solstitialis from both ranges derived only weak benefits from AM fungi. However, association with AM fungi was costly to plants when grown in competition with S. pulchra. The magnitude of the suppressive effect of AM fungi was greater for genotypes from native versus introduced populations., Synthesis. Many exotic invasive species are known to associate weakly with AM fungi, which may be beneficial in disturbed habitats where competition for resources is low. Our results indicate that reduced mycorrhizal associations may also benefit invaders in a competitive environment. Centaurea solstitialis were more strongly suppressed by established S. pulchra plants in the presence versus absence of AM fungi, but exotic genotypes were less suppressed than native genotypes. This suggests that AM fungi may contribute to invasion resistance in established native communities, but range-based shifts in the way exotic genotypes respond to AM fungal partners may counter such biotic resistance. [ABSTRACT FROM AUTHOR]

Successful exotic plant invasions are likely to be caused by multiple, non-mutually exclusive mechanisms, and it is exceptionally difficult to weight the relative importance of these mechanisms identified in different experiments. To this end we used individual-based models to explore how integrating empirical results from experiments might help to elucidate the relative importance of seed origin, biogeographic differences in competitive outcomes, and disturbance in exotic plant invasion. We integrated results from (1) competition experiments between Centaurea solstitialis derived from populations in the non-native range (California), the native range (Spain), and co-occurring native species from both ranges, (2) seed production by Centaurea plants from the different ranges grown in a common-garden environment, and (3) responses to disturbance experiments with plants from different native and non-native ranges. Californian C. solstitialis reached slightly higher abundances than its Spanish counterparts in every scenario, mainly due to higher seed production of Californians than their Spanish conspecifics, indicating the potential importance of evolutionary changes in the non-native range. In the absence of disturbance, grass species native to Europe showed stronger competitive effects on C. solstitialis than grass species native to North America, suggesting that release from competition in the native range may have some explanatory power for successful C. solstitialis invasion. However, the intensity of competition depended on the disturbance regime used in models. When intense disturbance was incorporated into the model, C. solstitialis was favored, with plants from Californian seed sources reaching higher densities than plants from Spanish seed sources. Our results are consistent with the idea that disproportional positive responses to disturbance in California, relative to those in the invader's native range of Spain, may be an important factor in the dominance of C. solstitialis in its non-native ranges. It is not clear why disturbance would have more beneficial effects on the invader in its non-native range, but the powerful effects of disturbance appear to interact in subtle ways with biogeographic differences in evolutionary trends, competitive intensities, life histories, and reproductive rates. [ABSTRACT FROM AUTHOR]

Yellow starthistle is an exotic invasive weed that is estimated to infest over 14 million acres in California and is considered the most common exotic weed statewide. We reviewed several previous studies and conducted a township survey to provide an up-to-date analysis of the weed's rapid spread throughout the state. A county-by-county comparison between 1985 and 2002 showed increases in yellow starthistle in all regions of the state except for northeast California and the southeast desert region. Currently, most infestations occur in Northern California, but future invasions and spread will likely occur in the coastal counties of Southern California.

We investigated indirect defense in the yellow starthistle ( Centaurea solstitialis)-grey garden slug ( Deroceras reticulatum)-ground beetle ( Pterostichus melanarius and Scaphinotus interruptus) system. In this host plant/herbivore/predator system, the ground beetles are the primary predator of D. reticulatum, the dominant herbivore of the highly invasive weed, C. solstitialis. The aim of our study was to examine the behavioral responses of two species of ground beetle to olfactory stimuli emitted from yellow starthistle damaged by D. reticulatum. The beetle P. melanarius showed a significant preference for the odor of damaged yellow starthistle relative to the odor of intact plants, while S. interruptus did not. Volatiles from D. reticulatum-damaged yellow starthistle were collected and identified as trans- β-farnesene, germacrene D, bicyclogermacrene, and 1,5,9-trimethyl-1,5,9-cyclododecatriene. No quantitative relationship was observed between beetle plant choice or decision time and the level of herbivory. Similarly, there was no relationship between volatile compound relative abundance and level of herbivory, suggesting that our range of leaf damage produces either undetectable semiochemicals or no variation in volatile emission. [ABSTRACT FROM AUTHOR]

Ecological filter models derived from community assembly theory can inform restoration planning by highlighting management actions most likely to affect community composition. Despite growing interest in these models, many restoration studies solely manipulate a single assembly filter - the biotic filter by altering interspecific competition - while ignoring abiotic and dispersal filters that may also influence restoration success., To examine how manipulating all three assembly filters (biotic, abiotic, dispersal) affected restoration in an annual-type grassland, we seeded native forbs from the same functional group as a target invader to increase biotic resistance to invasion (biotic filter), cut standing biomass and either removed it or returned it to plots as litter to alter light conditions (abiotic filter), and added native forbs at different seeding rates to alter density of establishing native populations (dispersal filter). We measured grassland restoration success by recording native species and invader cover in plots., The addition of native species with phenological and morphological traits similar to the target invader reduced invasion and increased native populations, but only in litter-free plots when high densities of native seed were added., Seeding two species with functional traits similar to the invader was more effective for achieving restoration goals than seeding just one functionally similar species. As such, trait differences among restoration species, even species belonging to the same functional group, may increase biotic resistance to invasion in restored communities., Litter removal altered native-invader interactions. When litter was left on the plots, added natives did not reduce invader cover. However, when litter was removed, added natives led to declines in invader cover., Increasing native seeding rates led to larger native populations and increased invasion resistance., Synthesis and applications. In this study, simultaneously manipulating biotic, abiotic and dispersal filters was necessary to optimize grassland restoration outcomes. In particular, the biotic filter only contributed to successful restoration outcomes under abiotic and dispersal conditions that were created through management actions specifically targeting these two additional filters. Restoration planning based on filter models should incorporate actions that target all three assembly filters, rather than solely focusing on the biotic filter. [ABSTRACT FROM AUTHOR]

The article offers information on the interactions among the biocontrol agents, pollinators, and an invasive weed. It discusses the impact of herbivores, seed predators, and pollinators on their host plants. It further mentions the importance of biological control of invasive plants as most invaders are attacked by their multiple agents.

Over the past 3 centuries, many species have been dispersed beyond their natural geographic limits by humans, but to our knowledge, reproductive isolation has not been demonstrated for such neo-allopatric species. We grew seeds from three species of Centaurea (Centaurea solstitialis, Centaurea calcitrapa, and Centaurea sulphurea) that are native to Spain and have been introduced into California, and we tested to what extent seed production was affected by pollen source. Compared with within-population crosses, seed production decreased by 52% and 44%, respectively, when C. solstitialis and C. sulphurea from California were pollinated with conspecific pollen from native populations in Spain. This implies rapid evolution of reproductive isolation between populations in their native and nonnative ranges. Whether reproductive isolation has evolved following the introduction of other species is unknown, but additional cases are likely, considering the large number of neoallopatric species. [ABSTRACT FROM AUTHOR]

Abstract: A longstanding hypothesis (“Baker''s rule”) is that plant invasiveness is facilitated by floral self compatibility rather than self incompatibility. Extending this idea, invasive species whose individuals vary in degree of self compatibility within the native range might be self compatible in invading or weedy populations, due to natural selection on the mating system. We compared mating system between native and invasive ranges for two major world invasives, one annual (Echium plantagineum) and one perennial (Solanum elaeagnifolium). For an additional annual species (Centaurea solstitialis) we compared non-weedy and weedy populations in the native range. No species was strongly spontaneously self pollinating, but the degree of self compatibility after hand pollination varied dramatically. Both annuals were self incompatible in native or non-weedy populations but self compatible in invasive or weedy ones; the reverse was true for the perennial. Individuals within populations of all three species also varied in their degree of self compatibility, suggesting a basis for natural selection, and populations of the same species sharing a status (native/non-weedy, invading/weedy) varied in average self compatibility. These results support the hypothesis that differential selection of progeny during invasion can result in self-compatible populations derived from ancestrally self-incompatible ones, but that this process may be less important in perennial species, which experience multiple opportunities for sexual reproduction. Overall, however, mating system may not operate alone and its contributions to invasiveness may be conditional on other attributes of a species including physiology, morphology, and life history. [Copyright &y& Elsevier]

The effects of declining plant biodiversity on ecosystem processes are well studied, with most investigations examining the role of species richness declines rather than declines of species abundance. Using grassland mesocosms, we examined how the abundance of a native, resident species, Hemizonia congesta (hayfield tarweed), affected exotic Centaurea soistitialis (yellow starthistle) invasion. We found that progressive H. congesta abundance declines had threshold effects on invasion resistance, with initial declines resulting in minor increases in invasion and subsequent declines leading to accelerating increases in invader performance. Reduced invasion resistance was explained by increased resource availability as H. congesta declined. We also found evidence that resident abundance might indirectly affect invasion by mediating invader impact on resident competitors; C. solstiiialis disproportion- ately reduced H. congesta biomass in low-abundance rather than high-abundance populations. H. congesta's direct and indirect effects on invasion resistance illustrate that an individual species' declining abundance can have accelerating, deleterious effects on ecosystem functions of conservation value. [ABSTRACT FROM AUTHOR]

Centaurea solstitialis (yellow starthistle, Asteraceae) is an invasive annual weed in the western USA that is native to the Mediterranean Region and is a target for classical biological control. Aceria solstitialis is an eriophyid mite that has been found exclusively in association with Ce. solstitialis in Italy, Greece, Turkey and Bulgaria. The mite feeds on leaf tissue and damages bolting plants, causing stunting, witch's broom and incomplete flower development. Field experiments and laboratory no-choice and two-way choice experiments were conducted to assess host plant specificity of the mite in Bulgaria. Mites showed the highest degree of host specificity in the field and lowest in the no-choice experiments. In the field, highest densities of mites occurred on Ce. solstitialis and Ce. cyanus (bachelor's button), and either no mites or trace numbers occurred on the other test plants: Ce. diffusa (diffuse knapweed), Carthamus tinctorius (safflower) and Cynara scolymus (artichoke). In no-choice experiments, mites persisted for 60 days on Ce. diffusa, Ce. cyanus, Ce. solstitialis, Ca. tinctorius and Cy. scolymus, whereas in two-way choice experiments mites persisted on 25% of Cy. scolymus plants for 60 days and did not persist on Ca. tinctorius beyond 40 days. The eight other species of plants that were tested in the laboratory were less suitable for the mite. These results suggest that although A. solstitialis can persist on some nontarget plants for as long as 60 days in the laboratory, it appears to be much more specific under natural conditions, and warrants further evaluation as a prospective biological control agent. [ABSTRACT FROM AUTHOR]

Background and Aims: Seeds buried in the soil detect burial depth through light and diurnally fluctuating temperatures (DFT) and in this way limit losses due to germination too deep in the soil. DFTs and germination also increase in vegetation gaps. However, dry open environments with high DFTs can also increase seedling mortality, creating conflicting selection pressures for reaction to DFTs. Since this questions the general function of DFT detection, we therefore tested if interspecific differences in DFT detection are related to mortality in different soil depths. Methods: We buried seeds of ten annual plants including species pairs of increasing and decreasing germination in response to DFTs. Seeds were buried in 5, 10 and 25cm soil depth and exhumed after two different burial times. Seed viability was tested using germination in growth chambers and tetrazolium. We also measured DFTs at these depths using temperature data loggers. Results: DFT detection was not related to differences in mortality at three burial depths. Three species showed a clear pattern of depth dependent mortality, however inconsistently related to DFT detection. Conclusions: Depth detection mechanisms are more species-specific than expected. Hence, interspecific differences in seed mortalities are difficult to predict by DFT detection alone and alternative soil depth sensing mechanisms should be explored in future. [ABSTRACT FROM AUTHOR]

Biological invasions are ubiquitous ecological phenomena that often impact native ecosystems. Some introduced species have evolved traits that enhance their ability to compete and dominate in recipient communities. However, it is still unknown if introduced species can evolve traits that may enhance their species interactions to fuel invasion success. We tested whether Centaurea solstitialis (yellow starthistle) from introduced populations have greater performance than native counterparts, and whether they generate more beneficial plant-soil interactions. We used common garden and plant-soil feedback experiments with soils and seeds from native Eurasian and introduced Californian populations. We found that performance of Centaurea did not differ among source genotypes , implying that the success of this invasive species is not due to evolutionary changes. However, Centaurea grew significantly larger in soils from introduced regions than from native regions, indicating a reduction in natural enemy pressure from native populations. We conclude that species interactions, not evolution, may contribute to Centaurea's invasion success in introduced populations. [ABSTRACT FROM AUTHOR]

Abstract: Six insect biocontrol agents have been introduced, with limited success, for managing the invasive plant yellow starthistle (Centaurea solstitialis). In 2003, a recently introduced fungal rust agent, Puccinia jaceae var. solstitialis, was approved for release in California. The presence of the rust in this multi-species complex was evaluated for its effect on performance of the two most common insect biocontrol agents for yellow starthistle, Chaetorellia succinea and Eustenopus villosus. To accomplish this, yellow starthistle was planted in 1m2 plots in monocultures at three densities and in a competition replacement series with wild oat (Avena fatua) in both 2006 and 2007. Twenty seedheads were dissected from each plot to evaluate the effect of P. jaceae on seedhead maturation and insect attack rate. In the replacement series experiment in 2007 and in 2006 and 2007 combined, P. jaceae caused a 35% and 20% increase, respectively, in the proportion of mature seedheads compared to total seedheads. However, there were no significant differences in the density experiment in either year or in the replacement series experiment in 2006. Although P. jaceae appeared to have a slight effect on yellow starthistle seedhead maturation, there was no effect of the rust on seedhead attack rates of either insect biological control, regardless of the experiment or year. These results indicate that P. jaceae does not interact significantly with the insect biological control agents for yellow starthistle. [Copyright &y& Elsevier]

Abstract: The rust fungus Puccinia jaceae var. solstitialis was introduced to California in 2003 for biological control of yellow starthistle (Centaurea solstitialis). To test its effectiveness under field conditions, we examined biomass production, chlorophyll levels, and seedhead production of yellow starthistle (YST) infected with P. jaceae. We also evaluated the effect of P. jaceae on the competitive ability of YST grown with wild oat (Avena fatua), a widespread winter annual grass commonly associated with YST infestations. Chlorophyll levels were reduced by over 50% in severely rust-infested YST leaves. P. jaceae had no effect on growth or reproductive variables in monoculture plots, but caused a modest reduction in YST performance in the competition experiment. In this study, infected plants had fewer leaves than uninfected plants and slightly reduced rosette diameters. P. jaceae also decreased YST biomass from 3.18kgm−2 in non-inoculated competition plots to 2.62kgm−2 in inoculated plots over both years of the experiment. Although not significant, there was a trend towards reduced seedhead production in the inoculated plots. These results indicate that P. jaceae may have some negative effects on YST growth, especially under conditions of interspecific competition. However, the effects of P. jaceae appear to be of minor biological significance and are unlikely to cause major declines in YST populations statewide. [Copyright &y& Elsevier]

Plant community functional composition can be manipulated in restored ecosystems to reduce the establishment potential of invading species. This study was designed to compare invasion resistance among communities with species functionally similar or dissimilar to yellow starthistle ( Centaurea solstitialis), a late-season annual. A field experiment was conducted in the Central Valley of California with six experimental plant communities that included (1) six early-season native annual forbs (AF); (2) five late-season native perennials and one summer annual forb (NP); (3) a combination of three early-season native annual forbs and three late-season native perennials (FP); (4) six early-season non-native annual grasses (AG); (5) monoculture of the late-season native perennial grass Elymus glaucus (EG); and (6) monoculture of the late-season native perennial Grindelia camporum (GC). Following establishment, C. solstitialis seed was added to half of the plots, and a monoculture of C. solstitialis (CS) was established as a control. Over a 5-year period, the AF and AG communities were ineffective at preventing C. solstitialis invasion. Centaurea solstitialis cover remained less than 10% in the FP and NP communities, except in year 1. By the fourth year, E. glaucus cover was greater than 50% in NP and FP communities and had spread to all other communities (e.g., 27% cover in CS in year 5). Communities containing E. glaucus, which is functionally similar to C. solstitialis, better resisted invasion than communities lacking a functional analog. In contrast, G. camporum, which is also functionally similar to C. solstitialis, failed to survive. Consequently, species selection for restored communities must consider not only functional similarity to the invader but also establishment success, competitiveness, and survivorship. [ABSTRACT FROM AUTHOR]

Abstract: Molecular analyses can play a primary role in the process of host specificity evaluation at species and population levels. Here we present an example of their application with a promising candidate biological control agent for yellow starthistle, Centaurea solstitialis L. Although it is highly host specific, Ceratapion basicorne (Coleoptera: Apionidae) can develop on safflower in laboratory tests. A field experiment was conducted to further evaluate host plant specificity; however, it was not possible to rear all larvae to the adult stage, which was necessary for species determination. Therefore molecular genetic methods were used to identify immature specimens. A 731bp fragment of mtDNA cytochrome C oxidase I gene (COI) was sequenced from 41 individuals of C. basicorne and four congeners: Ceratapion orientale, Ceratapion onopordi, Ceratapion penetrans and Ceratapion scalptum. Intraspecific variability ranged from 0.0% to 0.2%, and interspecific divergences ranged from 1.7% to 17.6%. All larvae that were sequenced from the field study, clearly matched one of the five species, enabling us to unambiguously identify them. Use of molecular genetics to identify larvae should also help the process of foreign exploration, enabling the identification of field-collected larvae, which often provide more reliable host plant associations than field collected adults. [Copyright &y& Elsevier]

Summary: Three sesquiterpene lactones (centaurepensin=chlorohyssopifolin A, chlorojanerin and 13-acetyl solstitialin A) isolated from the aerial parts of Centaurea solstitialis L. ssp. solstitialis (Asteraceae) were investigated for antimicrobial and antiviral activities. For the antimicrobial activity assessment, both standard and isolated strains of Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Staphylococcus aureus, Candida albicans and C. parapsilosis were employed by the microdilution method. Herpes simplex type-1, a DNA virus, and Parainfluenza, an RNA virus, were employed for the determination of the antiviral activity of these three sesquiterpene lactones using Vero cell lines. Ampicilline, ofloxocine, ketoconazole, fluconazole, acyclovir and oseltamivir were used as the reference drugs. 13-Acetyl solstitialin A displayed remarkable antibacterial activity against isolated strains of E. faecalis at 1μg/ml concentration, which was close to the effective concentrations of ampicillin. The same compound also showed significant activity against the DNA virus, being as potent as the reference compound acyclovir at maximum and minimum concentrations of 16–<0.00006μg/ml. This is the first report showing that 13-acetyl solstitialin A possesses significant antiviral activity. [Copyright &y& Elsevier]

Abstract: In anticipation of large-scale distribution of a Turkish isolate of Puccinia jaceae var. solstitialis in California for biological control of yellow starthistle (Centaurea solstitialis, YST), susceptibility of YST within the state was determined and a protocol for bulk inoculum production was developed. Inoculation was made of 62 field accessions of YST representative of the range of habitats in California. These were determined to be equally susceptible to infection by the isolate approved for release in the United States in 2003. To support a program to speed establishment by release at many locations statewide, protocols for artificial increase of inoculum were developed. Over 64g of urediniospores were produced with a mass-production system under greenhouse conditions from 2003 to 2006. Yield of inoculum varied by season, with peak production occurring from early spring through early summer. A large-scale urediniospore harvest also was made from a field plot at Davis, California. Our results show that susceptibility of YST in California is not likely to limit establishment of P. jaceae for biological control, and that production of this or other obligate pathogenic fungi (biological control agent) is possible for support of statewide release and research programs. [Copyright &y& Elsevier]

Background and Aims: Seed survival in the soil contributes to population persistence and community diversity, creating a need for reliable measures of soil seed bank persistence. Several methods estimate soil seed bank persistence, most of which count seedlings emerging from soil samples. Seasonality, depth distribution and presence (or absence) in vegetation are then used to classify a species' soil seed bank into persistent or transient, often synthesized into a longevity index. This study aims to determine if counts of seedlings from soil samples yield reliable seed bank persistence estimates and if this is correlated to seed production. [ABSTRACT FROM PUBLISHER]

We compared nectar secretion rates and bee guilds of yellow star-thistle, Centaurea solstitialis, on Santa Cruz Island (USA) and the Northeast Aegean Island of Lesvos (Greece). This plant species is non-native and highly invasive in the western USA but native to Eurasia (including Lesvos). "Nectar flow" was assessed by measuring nectar volumes in florets of flower heads covered with mesh bags (preventing visitation by bees); "nectar standing crop" data were taken from open (unbagged) flower heads to which all bees could gain access. We censused bees at C. solstitialis during comparable periods on both islands and determined the bee guild composition of the plant on Lesvos. Significant differences in nectar levels occurred between bagged and unbagged florets at each locale, especially during the period that pollinators were most common. Nectar flow and nectar standing crop volumes were lower on Lesvos than on Santa Cruz Island. The bee guild diversity at Lesvos was higher relative to Santa Cruz Island. Surprisingly, however, honey bees were not recorded during our monitoring periods on Lesvos. [ABSTRACT FROM AUTHOR]