Effects of mixtures of allelopathic plant water extracts and a herbicide on weed suppression

The present study investigated integrated effects of two allelopathic plant water extracts (WE) (Ambrosia artemisiifolia [AMBEL] and Xanthium strumarium [XANST]) and a herbicide (mesotrione) on morphological (height and fresh weight of plants) and physiological (pigments content) parameters of Abutilon theophrasti and Chenopodium album. Also, the study aimed to identify the main components of AMBEL and XANST WE and to evaluate their potential allelopathic effects. Of the 18 investigated compounds, 13 were detected in both tested WE, and p-coumaric acid was the leading component in AMBEL, while quinic acid was the predominant component of XANST. The WE of both weed species and their mixtures with the herbicide exhibited more powerful allelopathic effects on fresh weight and content of pigments than on the height of A. theophrasti and C. album. The results showed that all measured parameters of both weeds were inhibited in treatments with mesotrione and its mix with AMBEL and XANST WE. The data revealed a highly significant difference in effects (P < 0.05) between control weeds and those treated with AMBEL WE and mesotrione, where the inhibition of fresh weight was over 90%, while the inhibition of pigments content exceeded 80%, and plant height was inhibited by over 70%.

The response of Chenopodium album L. and Abutilon theophrasti Medik. to reduced doses of mesotrione

The application of minimal doses of herbicides is very popular due to concerns about the negative impacts of herbicides on the environment and public health. Studies were conducted to estimate the possibility of using quick and non- destructive methods to investigate Chenopodium album L. and Abutilon theophrasti Medik. response to mesotrione. The studies were conducted in a controlled environment to determine the response of C. album and A. theophrasti to mesotrione using dose-response curves created based on plant dry weight, chlorophyll fluorescence parameters and chlorophyll content. The obtained effective dose values showed that the studied weeds were susceptible to reduced doses of mesotrione. ED₉₅ values estimated for both species for dry weight and chlorophyll fluorescence parameters were lower than the recommended dose rate (120 g a.i. ha^-1), with less than 85 g a.i. ha^-1 needed to achieve a reduction of 95%, compared with untreated plants, while ED₉₅ value (A. theophrasti: 182 g a.i. ha^-1 and C. album: 180 g a.i. ha^-1) for chlorophyll content for both species was above the recommended dose rates. Consequently, dry weight and the chlorophyll fluorescence parameters are suitable for estimating the plant response to mesotrione, while chlorophyll content is not.

Fitness costs associated with multiple resistance to dicamba and atrazine in Chenopodium album

Detrimental pleiotropic effects of resistance mutation(s) were observed for multiple-resistant phenotypes (resistant to both atrazine and dicamba). The multiple-resistant phenotypes had lower growth rates and less capacity for vegetative growth compared to the phenotypes only resistant to atrazine. The fitness costs that are conferred by herbicide resistance alleles can affect the rate of herbicide resistance evolution within populations. We evaluated the direct fitness costs involved with multiple resistance to dicamba and atrazine (R1 and R2) in Chenopodium album by comparing the performance of multiple-resistant phenotypes to those phenotypes that were only resistant to atrazine (S1 and S2). The R1 and R2 phenotypes were consistently shorter and produced less dry matter than the S1 and S2 phenotypes. The R1 and R2 phenotypes were shown to have lower relative growth rates (RGR) and net assimilation rates (NAR) than the S1 and S2 phenotypes at an early stage of growth. However, there was no significant difference in RGR between the R1 and R2 and, S1 and S2 phenotypes at a later stage of growth, though the R1 and R2 phenotypes still had a lower NAR at this later stage. Further investigations using a neighbouring crop competition approach showed that the R1 and R2 phenotypes were weaker competitors, and exhibited significantly less capacity for vegetative growth compared to the S1 and S2 phenotypes during competition. Overall, the results of this study revealed multiple- resistance to atrazine and dicamba endowed a significant fitness penalty to C. album, and it is possible that the frequency of multiple-resistant individuals would gradually decline once selection pressure from herbicides was discontinued.

Increased temperatures and elevated CO2 levels reduce the sensitivity of Conyza canadensis and Chenopodium album to glyphosate

Herbicides are the most commonly used means of controlling weeds. Recently, there has been growing concern over the potential impacts of global climate change, specifically, increasing temperatures and elevated carbon dioxide (CO2) concentrations, on the sensitivity of weeds to herbicides. Here, glyphosate response of both Conyza canadensis and Chenopodium album was evaluated under different environmental conditions. Reduced glyphosate sensitivity was observed in both species in response to increased temperature, elevated CO2 level, and the combination of both factors. Increased temperature had greater effect on plant survival than elevated CO2 level. In combination, high temperature and elevated CO2 level resulted in loss of apical dominance and rapid necrosis in glyphosate-treated plants. To investigate the mechanistic basis of reduced glyphosate sensitivity, translocation was examined using 14C-glyphosate. In plants that were subjected to high temperatures and elevated CO2 level, glyphosate was more rapidly translocated out of the treated leaf to shoot meristems and roots than in plants grown under control conditions. These results suggest that altered glyphosate translocation and tissue-specific sequestration may be the basis of reduced plant sensitivity. Therefore, overreliance on glyphosate for weed control under changing climatic conditions may result in more weed control failures.

A global perspective on the biology, impact and management of Chenopodium album and Chenopodium murale: two troublesome agricultural and environmental weeds

Chenopodium album and C. murale are cosmopolitan, annual weed species of notable economic importance. Their unique biological features, including high reproductive capacity, seed dormancy, high persistence in the soil seed bank, the ability to germinate and grow under a wide range of environmental conditions and abiotic stress tolerance, help these species to infest diverse cropping systems. C. album and C. murale grow tall and absorb nutrients very efficiently. Both these species are allelopathic in nature and, thus, suppress the germination and growth of native vegetation and/or crop plants. These weed species infest many agronomic and horticultural crops and may cause > 90% loss in crop yields. C. album is more problematic than C. murale as the former is more widespread and infests more number of crops, and it also acts as an alternate host of several crop pests. Different cultural and mechanical methods have been used to control these weed species with varying degrees of success depending upon the cropping systems and weed infestation levels. Similarly, allelopathy and biological control have also shown some potential, especially in controlling C. album. Several herbicides have been successfully used to control these species, but the evolution of wide-scale herbicide resistance in C. album has limited the efficacy of chemical control. However, the use of alternative herbicides in rotation and the integration of chemicals and biologically based control methods may provide a sustainable control of C. album and C. murale.

Herbicide hormesis can act as a driver of resistance evolution in weeds - PSII-target site resistance in Chenopodium album L. as a case study

BACKGROUND

Herbicide hormesis may play a role in the evolution of weed resistance by increasing resistance selection. A standard herbicide rate may be subtoxic to resistant plants and make them more fit than untreated plants. If this increase in fitness is ultimately expressed in reproductive traits, resistance genes can accumulate more rapidly and exacerbate resistance evolution by magnifying the selection differential between resistant and sensitive plants. The hypothesis of hormetically enhanced reproductive fitness was studied for a photosystem II (PSII) target-site resistant (TSR) biotype of Chenopodium album exposed to the triazinone metamitron in comparison with its wild-type.

RESULTS

Both biotypes showed an initial hormetic growth increase at different doses leading to fitness enhancements of between 19% and 61% above untreated plants. However, hormetic effects only resulted in higher fitness at maturity in resistant plants with a maximum stimulation in seed yield of 45% above untreated plants. Applying realistic metamitron rates, reproductive fitness of resistant plants was increased by 15-32%.

CONCLUSIONS

Agronomically relevant doses of metamitron induced considerable hormesis in a PSII-TSR C. album genotype leading to enhanced relative fitness through reproductive maturity. This increase in relative fitness suggests an impact on resistance selection and can compensate for the oft-reported fitness costs of the mutation studied. Field rates of herbicides can, thus, not only select for resistant plants, but also enhance their reproductive fitness. The finding that herbicide hormesis can be eco-evolutionary important may have important implications for understanding the evolution of herbicide resistance in weeds. © 2018 Society of Chemical Industry.

Ammonium 2,2'-thiodiacetates - Selective and environmentally safe herbicides

2,2'-Thiodiacetic acid derivatives have a wide application potential, mainly in coordination chemistry. This research indicates that quaternary ammonium 2,2'-thiodiacetate salts may also be potent herbicidal agents used in agriculture. To provide a rationale for this statement, the toxic effect by a alkyl and aryl quaternary ammonium salts (QASs) on plant growth was investigated. The phytotoxicity of these compounds was tested against cultivated monocotyledonous (spring barley) and dicotyledonous (common radish) plants, whereas herbicidal activity was investigated in relation to popular weeds species (white goosefoot, sorrel and gallant-soldier). The results showed that aliphatic QASs possessed a low phytotoxicity to food crops and that some of them (in particular triethylammonium salt) had potent and selective herbicidal properties against common weeds, such as sorrel and gallant-soldier. However, the investigated compounds appeared to be ineffective herbicides against white goosefoot.

Herbicidal activity of slow-release herbicide formulations in wheat stands infested by weeds

The present study reports the herbicidal activity of metribuzin and tribenuron-methyl embedded in the degradable matrix of natural poly-3-hydroxybutyrate [P(3HB)/MET and P(3HB)/TBM]. The developed formulations were constructed as films and microgranules, which were tested against the weeds such as white sweet clover Melilotus albus and lamb's quarters Chenopodium album in the presence of soft spring wheat (Triticum aestivum, cv. Altaiskaya 70) as the subject crop for investigation. The activity was measured in laboratory scale experiments by determining the density and weight of the vegetative organs of weeds. The study was also aimed at testing the effect of the experimental formulation on the growth of wheat crop as dependent on the method of herbicide delivery. The experimental MET and TBM formulations showed pronounced herbicidal activity against the weed species used in the study. The effectiveness of the experimental formulations in inhibiting weed growth was comparable to and, sometimes, higher than that of the commercial formulations (positive control). The amount of the biomass of the wheat treated with the experimental herbicide formulations was significantly greater than that of the wheat treated with commercial formulations.

Natural herbicide activity of Satureja hortensis L. essential oil nanoemulsion on the seed germination and morphophysiological features of two important weed species

The aim of the present study was to obtain an oil/water (O/W) nanoemulsion (NE) containing garden savory (Satureja hortensis) essential oil (EO) and evaluating its herbicidal activity against Amaranthus retroflexus and Chenopodium album. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were employed to determine the chemical composition of the EO. Carvacrol (55.6%) and γ-terpinene (31.9%) were the major EO components. Low energy method was applied, allowing achievement of EO nanodroplets. The NE also presented low polydispersity, and the mean droplet was below 130nm even after storage for 30d. Laboratory tests showed that the NE at different concentrations (100, 200, 400, 800, and 1000μL.L^-1) significantly (P≤0.05) reduced the germination indices and the seedling's growth in dose-response. The inhibitory effect was the greatest at 800μL.L^-1 NE. Overall, root length was more inhibited as compared to shoot length. Post-emergence application of NE at different concentrations (1000, 2000, 3000, 4000 and 5000μL.L^-1 of EO) on 2-4 true leaves' stage of the weeds caused significant (P≤0.05) decrease in the growth factors in dose-dependent manner. Complete lethality was observed by 4000μL.L^-1 NE sprayed on the weeds. Spraying of NE significantly (P≤0.05) reduced chlorophyll content in the tested weeds. Increasing in relative electrolyte leakage (REL) 1 and 5d after treatment represented significant cell membrane disruption and increased cell membrane permeability. Transmission electron microscope (TEM) pictures confirmed NE droplet size and demonstrated membrane destruction. The study approved that the NE of S. hortensis EO has herbicidal properties as it has high phytotoxic effect, and interferes with the germination, growth and physiological processes of the weeds. The production of NE from S. hortensis EO is a low energy method that offers a promising practical natural herbicide for weed control in organic agricultural systems.

Alkyl(C16, C18, C22)trimethylammonium-Based Herbicidal Ionic Liquids

In the framework of this study a synthesis methodology and characterization of long alkyl herbicidal ionic liquids (HILs) based on four commonly used herbicides (2,4-D, MCPA, MCPP, and dicamba) are presented. New HILs were obtained with high efficiency (>95%) using an acid-base reaction between herbicidal acids and hexadecyltrimethylammonium, octadecyltrimethylammonium, and behenyltrimethylammonium hydroxides in alcoholic medium. Among all synthesized salts, only three compounds comprising the MCPP anion were liquids at room temperature. Subsequently, the influence of both the alkyl chain length and the anion structure on their physicochemical properties (thermal decomposition profiles, solubility in 10 representative solvents, surface activity, density, viscosity, and refractive index) was determined. All HILs exhibited high thermal stability as well as surface activity; however, their solubility notably depended on both the length of the carbon chain and the structure of the anion. The herbicidal efficacy of the obtained salts was tested in greenhouse and field experiments. Greenhouse testing performed on common lambsquarters (Chenopodium album L.) and flixweed (Descurainia sophia L.) as test plants indicated that HILs were characterized by similar or higher efficacy compared to commercial herbicides. The results of field trials confirmed the high activity of HILs, particularly those containing phenoxyacids as anions (MCPA, 2,4-D, and MCPP).

Antifungal and Herbicidal Effects of Fruit Essential Oils of Four Myrtus communis Genotypes

The chemical composition of the essential oils isolated by hydrodistillation from the fruits of four selected Myrtus communis L. genotypes from Turkey was characterized by GC-FID and GC/MS analyses. 1,8-Cineole (29.20-31.40%), linalool (15.67-19.13%), α-terpineol (8.40-18.43%), α-pinene (6.04-20.71%), and geranyl acetate (3.98-7.54%) were found to be the major constituents of the fruit essential oils of all M. communis genotypes investigated. The oils were characterized by high amounts of oxygenated monoterpenes, representing 73.02-83.83% of the total oil compositions. The results of the fungal growth inhibition assays showed that the oils inhibited the growth of 19 phytopathogenic fungi. However, their antifungal activity was generally lower than that of the commercial pesticide benomyl. The herbicidal effects of the oils on the seed germination and seedling growth of Amaranthus retroflexus L., Chenopodium album L., Cirsium arvense (L.) Scop., Lactuca serriola L., and Rumex crispus L. were also determined. The oils completely or partly inhibited the seed germinations and seedling growths of the plants. The findings of the present study suggest that the M. communis essential oils might have potential to be used as natural herbicides as well as fungicides.

Identification of a new PSII target site psbA mutation leading to D1 amino acid Leu218 Val exchange in the Chenopodium album D1 protein and comparison to cross-resistance profiles of known modifications at positions 251 and 264

BACKGROUND

Resistance of Chenopodium album to triazinones and triazines can be caused by two amino acid exchanges, serine-264-glycine (Ser(264) Gly) and alanine-251-valine (Ala(251) Val), in the chloroplast D1 protein. This paper describes the identification of a biotype with a leucine-218-valine (Leu(218) Val) switch found in German sugar beet fields with unsatisfactory weed control. A greenhouse experiment has been performed to compare the resistance profile of the newly identified biotype with biotypes that carry the Ser(264) Gly and Ala(251) Val mutations.

RESULTS

Application rate-response curves obtained from the greenhouse experiment showed that the Leu(218) Val exchange induced significant resistance against the triazinones but not against terbuthylazine. The level of resistance against the triazinones was higher in the Ser(264) Gly and Ala(251) Val biotypes compared with the Leu(218) Val biotype. All biotypes tested were more resistant to metribuzin than to metamitron. Following terbuthylazine treatment, Ser264 Gly displayed a high level of resistance, Ala(251) Val showed moderate resistance. A PCR-RFLP assay for Ser(264) Gly has been extended to include detection of Ala251 Val and Leu(218) Val mutations.

CONCLUSION

The D1 Leu(218) Val substitution in C. album confers significant resistance to triazinones. This suggests that Leu(218) Val is involved in the binding of triazinones. First establishment of the resistance profiles of the three psbA mutations suggests that these mutations have been independently selected.

Chenopodolin: a phytotoxic unrearranged ent-pimaradiene diterpene produced by Phoma chenopodicola, a fungal pathogen for Chenopodium album biocontrol

A new phytotoxic unrearranged ent-pimaradiene diterpene, named chenopodolin, was isolated from the liquid culture of Phoma chenopodicola, a fungal pathogen proposed for the biological control of Chenopodium album, a common worldwide weed of arable crops such as sugar beet and maize. The structure of chenopodolin was established by spectroscopic, X-ray, and chemical methods as (1S,2S,3S,4S,5S,9R,10S,12S,13S)-1,12-acetoxy-2,3-hydroxy-6-oxopimara-7(8),15-dien-18-oic acid 2,18-lactone. At a concentration of 2 mg/mL, the toxin caused necrotic lesions on Mercurialis annua, Cirsium arvense, and Setaria viride. Five derivatives were prepared by chemical modification of chenopodolin functionalities, and some structure-activity relationships are discussed.

Physiological responses and tolerance mechanisms to Pb in two xerophils: Salsola passerina Bunge and Chenopodium album L

Lead (Pb) has great toxicity to human beings and other livings. Although there are varied ways to rehabilitate the Pb contaminated area, phytoremediation of Pb pollution in arid lands is still a difficult task, it is therefore urgent to find and identify Pb tolerant plants in arid areas. The physiological responses and tolerance mechanisms to Pb stress (expressed as the Pb concentration, e.g., 0, 50, 150, 300, 600, 800, 1000 mg/L) were investigated for the xerophils Salsola passerina Bunge and Chenopodium album L. Results indicated that S. passerina exhibited higher Pb tolerance than Ch. album in terms of the seed germination rate, bio-activities of SOD and POD, and lower MDA production. There were two ways for S. passerina to reduce Pb toxicity in organism level, e.g., cell wall precipitation and state transfer of free Pb into anchorage. These findings demonstrate that S. passerina is a Pb tolerant species and may have potential application in phytoremediation of Pb contaminated arid lands.

The origin of metamitron resistant Chenopodium album populations in sugar beet

Chenopodium album L. is a major weed in spring-planted crops in the temperate regions of the world. Since 2000, farmers have reported an unsatisfactory control of this weed in sugar beet fields in Belgium, France and The Netherlands. Frequently, the surviving C. album plants are resistant to metamitron, a key herbicide in this crop. Metamitron resistance in C. album is caused by a Ser264 to Gly mutation in the psbA gene on the chloroplast genome, which prevents binding of metamitron to its target site. This mutation causes also resistance to other herbicides with a similar mode of action, like metribuzin -applied in potato- and atrazine in particular. Atrazine has been applied very frequently in maize in the 1970s and the 1980s, but is now banned in Europe due to environmental reasons. The persistent use of atrazine in maize confronted Belgian and other European farmers in the early 1980s with atrazine resistant C. album with the same Ser264 to Gly mutation. The problems with atrazine resistant C. album disappeared when other herbicides were applied in maize. Unfortunately, this is not the case for metamitron resistant C. album in sugar beet, because no replacement herbicide is readily available. The history of atrazine use in maize brought up a question concerning the origin of the current metamitron resistant C. album populations. Have these populations been selected locally by regular use of metamitron in sugar beet or did the selection occur earlier by atrazine use when maize was grown in the same fields? This would have serious implications regarding the reversibility of herbicide resistance. Therefore, soil samples were collected on 16 fields with different histories: five fields with an organic management over 25 years, two fields with a history of atrazine resistant C. album, five fields with metamitron resistant C. album in sugar beet and four fields which were under permanent grassland for 10 years, preceded by a regular rotation in which sugar beet was a key crop. The seeds of C. album were extracted from the soil and germinated on a germination table. Germinated seeds were allowed to grow in a growth chamber. Metamitron resistance was determined by a chlorophyll fluorescence test and leaf material was sampled for AFLP-analysis. For all fields, estimations were made of the size of the seed bank (i.e. an indirect estimate of population size), the frequency of resistant plants and the genetic diversity of resistant and susceptible populations. The results indicate that herbicide-resistant C. album populations are persistent and maintain their adaptive capacity, challenging future management of metamitron resistant C. album.

Local spread of metamitron resistant Chenopodium album L. patches

Molecular markers can provide valuable information on the spread of resistant weed biotypes. In particular, tracing local spread of resistant weed patches will give details on the importance of seed migration with machinery, manure, wind or birds. This study investigated the local spread of metamitron resistant Chenopodium album L. patches in the southwest region of the province West-Flanders (Belgium). During the summer of 2009, leaf and seed samples were harvested in 27 patches, distributed over 10 sugar beet fields and 1 maize field. The fields were grouped in four local clusters. Each cluster corresponded with the farmer who cultivated these fields. A cleaved amplified polymorphic sequence (CAPS) procedure identified the Ser264 to Gly mutation in the D1 protein, endowing resistance to metamitron, a key herbicide applied in sugar beet. The majority of the sampled plants within a patch (97% on average) carried this mutation. Amplified fragment length polymorphism (AFLP) analysis was performed with 4 primer pairs and yielded 270 molecular markers, polymorphic for the whole dataset (303 samples). Analysis of molecular variance revealed that a significant part of the genetic variability was attributed to variation among the four farmer locations (12 %) and variation among Chenopodium album patches within the farmer locations (14%). In addition, Mantel tests revealed a positive correlation between genetic distances (linearised phipt between pairs of patches) and geographic distances (Mantel-coefficient significant at p = 0.002), suggesting isolation-by-distance. In one field, a decreased genetic diversity and strong genetic relationships between all the patches in this field supported the hypothesis of a recent introduction of resistant biotypes. Furthermore, genetic similarity between patches from different fields from the same farmer and from different farmers indicated that seed transport between neighbouring fields is likely to have an important impact on the spread of metamitron resistant biotypes.

A new molecular method for the rapid detection of a metamitron-resistant target site in Chenopodium album

BACKGROUND

Resistance to photosystem II inhibitors-triazines (atrazine) and triazinones (metamitron, metribuzin)-in Chenopodium album L. is caused by the serine 264 to glycine mutation in the D1 protein. This mutation has been detected in C. album collections from Belgium with unsatisfactory metamitron efficacy in the field and was confirmed in greenhouse resistance bioassays. Incomplete herbicide efficacy in practice can also be caused by reduced uptake due to environmental conditions. Hence, for reliable differentiation and resistance identification, a rapid method for mutation detection in the target gene psbA is required.

RESULTS

Dose-response curves obtained in herbicide greenhouse assays with metamitron-resistant and -susceptible reference biotypes showed that a dose of 2 L ha(-1) metamitron was suitable for discrimination. A psbA PCR-RFLP was developed, based on the presence of a FspBI restriction enzyme recognition site, covering D1 codon 264 in susceptible genotypes. A paper-based DNA extraction allowed direct processing of leaf samples already in the field. In order to detect the mutation even in mixed seed samples, a nested PCR-RFLP was also developed.

CONCLUSION

The method allows exhaustive surveys screening C. album leaf or seed samples for the occurrence of the D1 Ser264Gly mutation to confirm or disprove metamitron resistance in the case of unsatisfactory control.

Variation of seed heteromorphism in Chenopodium album and the effect of salinity stress on the descendants

BACKGROUND AND AIMS

Chenopodium album is well-known as a serious weed and is a salt-tolerant species inhabiting semi-arid and light-saline environments in Xinjiang, China. It produces large amounts of heteromorphic (black and brown) seeds. The primary aims of the present study were to compare the germination characteristics of heteromorphic seeds, the diversity of plant growth and seed proliferation pattern of the resulting plants, and the correlation between NaCl stress and variation of seed heteromorphism.

METHODS

The phenotypic characters of heteromorphic seeds, e.g. seed morphology, seed mass and total seed protein were determined. The effects of dry storage at room temperature on dormancy behaviour, the germination response of seeds to salinity stress, and the effect of salinity on growth and seed proliferation with plants derived from different seed types were investigated.

KEY RESULTS

Black and brown seeds differed in seed morphology, mass, total seed protein, dormancy behaviour and salinity tolerance. Brown seeds were large, non-dormant and more salt tolerant, and could germinate rapidly to a high percentage in a wider range of environments; black seeds were salt-sensitive, and a large proportion of seeds were dormant. These characteristics varied between two populations. There was little difference in growth characteristics and seed output of plants produced from the two seed morphs except when plants were subjected to high salinity stress. Plants that suffered higher salinity stress produced more brown (salt-tolerant) seeds.

CONCLUSIONS

The two seed morphs of C. album exhibited distinct diversity in germination characteristics. There was a significant difference in plant development and seed proliferation pattern from the two types of seeds only when the parent plants were treated with high salinity. In addition, seed heteromorphism of C. album varied between the two populations, and such variation may be attributed, at least in part, to the salinity.

Chlorophyll fluorescence protocol for quick detection of triazinone resistant Chenopodium album L

Sugar beet growers in Europe are more often confronted with an unsatisfactory control of Chenopodium album L. (fat-hen), possibly due to the presence of a triazinone resistant biotype. So far, two mutations on the psbA-gene, i.e. Ser264-Gly and Ala251-Val, are known to cause resistance in C. album to the photosystem II-inhibiting triazinones metamitron, a key herbicide in sugar beet, and metribuzin. The Ser264-Gly biotype, cross-resistant to many other photosystem II-inhibitors like the triazines atrazine and terbuthylazine, is most common. The second resistant C. album biotype, recorded in Sweden, is highly resistant to triazinones but only slightly cross-resistant to terbuthylazine. Since farmers should adapt their weed control strategy when a resistant biotype is present, a quick and cheap detection method is needed. Therefore, through trial and error, a protocol for detection with chlorophyll fluorescence measurements was developed and put to the test. First, C. album leaves were incubated in herbicide solution (i.e. 0 microM, 25 microM metribuzin, 200 microM metamitron or 25 microM terbuthylazine) during three hours under natural light. After 30 minutes of dark adaptation, photosynthesis yield was measured with Pocket PEA (Hansatech Instruments). In Leaves from sensitive C. album, herbicide treatment reduces photosynthesis yield due to inhibition of photosynthesis at photosystem II. This results in a difference of photosynthesis yield between the untreated control and herbicide treatment. Based on the relative photosynthesis yield (as a percentage of untreated), a classification rule was formulated: C. album is classified as sensitive when its relative photosynthesis yield is less than 90%, otherwise it is resistant. While metribuzin, and to a lesser extent, metamitron treatment allowed a quick detection of triazinone resistant C. album, terbuthylazine treatment was able to distinguish the Ser264-Gly from the Ala251-Val biotype. As a final test, 265 plants were classified with the protocol. Simultaneously, a CLeaved Amplified Polymorphic Sequence (CAPS)-analysis was conducted on the same plants to verify the presence of the Ser264-Gly mutation. Only one mismatch was found when results of both detection methods were compared. The test results illustrate that this protocol provides a reliable, quick and cheap alternative for DNA-analysis and bio-assays to detect the triazinone resistant C. album biotypes.

Interactive effects of elevated CO2 and growth temperature on the tolerance of photosynthesis to acute heat stress in C3 and C4 species

Determining effects of elevated CO2 on the tolerance of photosynthesis to acute heat-stress (heat wave) is necessary for predicting plant responses to global warming, as photosynthesis is thermolabile and acute heat-stress and atmospheric CO2 will increase in the future. Few studies have examined this, and past results are variable, which may be due to methodological variation. To address this, we grew two C3 and two C4 species at current or elevated CO2 and three different growth temperatures (GT). We assessed photosynthetic thermotolerance in both unacclimated (basal tolerance) and pre-heat-stressed (preHS = acclimated) plants. In C3 species, basal thermotolerance of net photosynthesis (P(n)) was increased in high CO2, but in C4 species, P(n) thermotlerance was decreased by high CO2 (except Zea mays at low GT); CO2 effects in preHS plants were mostly small or absent, though high CO2 was detrimental in one C3 and one C4 species at warmer GT. Though high CO2 generally decreased stomatal conductance, decreases in P(n) during heat stress were mostly due to non-stomatal effects. Photosystem II (PSII) efficiency was often decreased by high CO2 during heat stress, especially at high GT; CO2 effects on post-PSII electron transport were variable. Thus, high CO2 often affected photosynthetic theromotolerance, and the effects varied with photosynthetic pathway, growth temperature, and acclimation state. Most importantly, in heat-stressed plants at normal or warmer growth temperatures, high CO2 may often decrease, or not benefit as expected, tolerance of photosynthesis to acute heat stress. Therefore, interactive effects of elevated CO2 and warmer growth temperatures on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.

Leaf angle in Chenopodium album is determined by two processes: induction and cessation of petiole curvature

Petiole curvature is important in regulating light interception by the leaf. To dissect the determination processes of leaf angle, we irradiated the lamina or petiole of Chenopodium album L. with either one or two spots of actinic light, after dark adaptation. When the abaxial side of the petiole was irradiated with blue light, the petiole curvature increased, and under continuous irradiation, the curvature continued for up to 6 h. The rate of curvature increased with increasing blue light intensity. The curvature induced by irradiation of the abaxial side with blue light ceased when the adaxial side of the petiole was simultaneously irradiated with either blue or red light. When an inhibitor for photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, was applied to the adaxial side of the petiole, the cessation of curvature caused by blue light was only weakly inhibited, while the cessation caused by red light was markedly inhibited. When the adaxial side of the petiole was irradiated alternately with red and far-red light, the far-red light antagonized the cessation of curvature caused by the red light. These results clearly show that the petiole curvature is controlled by two processes, the induction and the cessation of curvature. At least three photoreceptor systems, blue-light receptor, photosynthesis and phytochrome, are involved in the reactions.

Morphophysiological traits and atrazine sensitivity in Chenopodium album L

BACKGROUND

A Chenopodium album L. biotype surviving in atrazine-treated Serbian corn fields (VC) was compared against atrazine-susceptible (S) and atrazine-resistant (R) standards.

RESULTS

Atrazine (2 kg ha(-1)) killed S and VC shoot biomass 15 days after treatment (DAT), but R was only suppressed by 42% and survived 8 kg ha(-1). Atrazine at 2 kg ha(-1) only inhibited VC height by 60% as against 100 and 0% for S and R respectively. Chlorophyll fluorescence (Fv/Fm) and transpiration were insensitive to atrazine in R, but were inhibited by 90 and 100% in S and by 50 and 60% in VC respectively. Decline of Fv/Fm after 2 kg ha(-1) atrazine was stabilized at 3 DAT for the VC biotype.

CONCLUSION

A toxicity mitigation mechanism could have facilitated VC survival in an atrazine-treated field. Further knowledge on this mechanism is needed to establish if surviving VC plants are indicators of atrazine resistance evolution in these Serbian corn fields. Variables related to foliar function provided better detection of weed mechanisms to survive herbicide action than the usual shoot biomass measurements.

Resistance of Chenopodium albumto photosystem II-inhibitors

Chenopodium album L. (fat-hen), a highly competitive and very prolific species, is a common weed in most spring- and summer-sown crops such as maize, sugar beet and vegetables. In the late seventies, C. album stepped into the limelight as a problem weed in maize. Frequent use of atrazine in maize monoculture did select for plants having a Ser-264-Gly mutation on the psbA gene resulting in atrazine-resistance and cross-resistance to other Photosystem (PS) II-inhibitors. The psbA gene encodes the D1 protein of PS II which is the target site of PS II-inhibitors. Introduction of new herbicides made it possible to control this atrazine-resistant biotype in maize, which allowed C. album to fade into the background again until it resurfaced some years ago as a problem weed in European sugar beet (Belgium, France, The Netherlands and Sweden). Greenhouse bioassays at Ghent University revealed that the unsatisfactory control of C. album in sugar beet is due to resistance to the triazinone metamitron, a key herbicide in sugar beet. The expected cross-resistance to atrazine and metribuzin was found in all populations except for a Swedish one, which is highly resistant to metamitron and metribuzin but not to atrazine. DNA sequence analysis confirmed the presence of a Ser-264-Gly mutation for all populations that are both metamitron- and atrazine-resistant. The Swedish population has an Ala-251-Val mutation on the psbA gene explaining its aberrant (cross)-resistance profile. The occurrence of C. album biotypes with resistance to metamitron but different genotypes and cross-resistance profiles could raise the question which herbicide(s) did select for the resistance. In Sweden, having no history of atrazine use, the triazinones metamitron, used in sugar beet, and metribuzin, used in rotational potato, could have selected for resistance. In Belgium, at least three different herbicides and/or crop rotations could have contributed to resistance development: (1) a record of continuous use of atrazine in maize resulting in triazine-resistant C. album in the seed bank, (2) metamitron use in sugar beet and (3) metribuzin use in potato.

Chlorophyll fluorescence tests for monitoring triazinone resistance in Chenopodium album L

Recently, fat-hen (Chenopodium album L.) biotypes resistant to metamitron, a key herbicide in sugar beet, were recorded. Pot experiments revealed that these biotypes showed cross-resistance to metribuzin, a triazinone used in potato. Greenhouse and laboratory experiments were performed to develop resistance monitoring tests, so that resistant biotypes can be detected quickly and farmers may adapt their weed management. Resistant and susceptible biotypes were grown in a greenhouse under conditions of natural and artificial light at an intensity of 100 micromol photons m(-2) s(-1). Leaves were collected and, immersed in a solution of 1000 microM metamitron and 500 microM metribuzin, exposed to natural and artificial light (1000, 750 and 100 micromol photons m(-2) s(-1) respectively). After this, chlorophyll fluorescence measurements were carried out. The results revealed that the photosynthetic electron transport of metamitron- and metribuzin-incubated leaves of resistant biotypes decreased less than that of the incubated Leaves of susceptible biotypes. The differences between the metribuzin-incubated leaves of the susceptible and resistant biotypes were larger than those observed with the metamitron-incubated leaves. The aim of the experiments was to optimise the chlorophyll fluorescence test and to find a sufficiently high correlation between the results of the pot experiments and the chlorophyll fluorescence measurements.

Effect of selected sugar beet herbicides on germination of various Chenopodium album populations

Seeds of various fat-hen populations (Chenopodium album L.), mostly originating from sugar beet fields, were subjected to treatments with the following herbicides: metamitron, acetochlor, dimethenamid-P and S-metolachlor. Herbicides were applied either incorporated into a sandy Loam soil (2005-2007) and/or on filter paper in Petri dishes (2006-2007). Results between experiments were highly contrasting. Soil applications of metamitron, acetochlor and S-metolachlor were stimulating germination in the 2005 experiments, whereas in the 2006-2007 experiments effects were ranging from slightly stimulating to highly inhibitory.

The efficiency of adjuvants combined with flupyrsulfuron-methyl plus metsulfuron-methyl (Lexus XPE) on weed control

This paper presents the results of laboratory tests on a selection of weeds (Viola arvensis, Polygonum persicaria, Chamomilla recutita, Chenopodium album, Veronica persicaria, Alopecurus myosusroides) to investigate the efficiency of flupyrsulfuron-methyl plus metsutfuronmethyl (Lexus XPE) in combination with different adjuvants. The efficiency of the herbicide improved in combination of adjuvants. The level of phytotoxicity of the adjuvants-herbicide treatments appllied varied among the different weed species.

Cuticular uptake of xenobiotics into living plants. Part 2: influence of the xenobiotic dose on the uptake of bentazone, epoxiconazole and pyraclostrobin, applied in the presence of various surfactants, into Chenopodium album, Sinapis alba and Triticum aestivum leaves

This study has determined the uptake of three pesticides, applied as commercial or model formulations in the presence of a wide range of surfactants, into the leaves of three plant species (bentazone into Chenopodium album L. and Sinapis alba L., epoxiconazole and pyraclostrobin into Triticum aestivum L.). The results have confirmed previous findings that the initial dose (nmol mm(-2)) of xenobiotic applied to plant foliage is a strong, positive determinant of uptake. This held true for all the pesticide formulations studied, although surfactant concentration was found to have an effect. The lower surfactant concentrations studied showed an inferior relationship between the amount of xenobiotic applied and uptake. High molecular mass surfactants also produced much lower uptake than expected from the dose uptake equations in specific situations.

Metamitron-resistant Chenopodium album from sugar beet: cross-resistance profile

In recent years, in several of the Belgian sugar beet growing regions, farmers have been confronted with unsatisfactory control of fat hen (Chenopodium album L.). Greenhouse bioassays conducted on reference C. album populations and on "suspected" populations from sugar beet fields where poor fat hen control had been observed, revealed that all "suspected" populations were resistant to metamitron, a key herbicide in the modern low rate weed control programs in sugar beet. These metamitron-resistant biotypes were all cross-resistant to atrazine. Since cross-resistance, particularly negative cross-resistance or reversed resistance, is known to play a major role in resistance management, other herbicides used in sugar beet and/or in rotational crops were tested to determine the cross-resistance profile of metamitron-resistant biotypes. Greenhouse bioassays were conducted using herbicides from different chemical families representing different modes of action. Cross-resistance was found for metribuzin, lenacil and chloridazon, all HRAC Group C1 herbicides that inhibit photosynthesis at PS II. The metamitron-resistant C. album populations examined showed negative cross-resistance to S-metolachlor (HRAC Group K3: inhibition of cell division), prosuifocarb (Group N: lipid synthesis, not AC-Case, inhibition), aclonifen and clomazone (both Group F3: inhibition of carotenoid biosynthesis).

Resistance to metamitron in Chenopodium album from sugar beet. a tale of the (un)expected?

Metamitron is a key herbicide in modern low rate weed control programs in sugar beet. Fat hen (Chenopodium album, CHEAL) is a common, highly competitive, weed in sugar beet and one of the targets of metamitron. Recently, unsatisfactory control of fat hen has been reported in several sugar beet fields situated in various regions in Belgium. Weather conditions as well as the mere fact of using low rate systems have been blamed for these poor performances. To address the question "Is the recently recorded poor control of C. album due to decreased sensitivity to metamitron", greenhouse bioassays were carried out. A first experiment was conducted applying metamitron (0, 350, 700 and 1,400 g ai/ha) postemergence to three "suspected" C. album populations originating from sugar beet fields with unsatisfactory control by standard metamitron based treatment schemes ('Ligne', 'Outgaarden' and 'Boutersem I' respectively) and to one sensitive population originating from an untreated garden site ('Gent'). In a second experiment seven population, five "suspected" fat hen populations from sugar beet fields ('Boutersem I', 'Boutersem II', 'Postel', 'Vissenaken' and 'Kortessem' respectively), one sensitive reference population 'Herbiseed' and one atrazine-resistant reference population 'ME.85.01', were submitted to metamitron (0, 1, 2 and 4 mg ai/kg air-dry soil) and atrazine (1.5 mg ai/kg air-dry soil) preplant incorporated. All "suspected" C. album populations displayed a significantly lower sensitivity to metamitron compared to the sensitive populations ('Gent' and 'Herbiseed') that never had been exposed to this herbicide. As target site cross-resistance of atrazine-resistant C. album, selected by atrazine in maize, to metamitron has been known for a long time, cross-resistance of C. album populations in sugar beet grown on fields with "maize - atrazine" containing rotations might be expected to appear. The outcome of the experiment with atrazine preplant incorporated was the confirmation of resistance in all "suspected" populations ('Boutersem I', 'Boutersem II', 'Postel', 'Vissenaken' and 'Kortessem'). However, some "suspected" populations came from fields with no background of cropping with maize and use of atrazine. So, the question remains whether these triazine-resistant C. album had been imported, e.g. with slurry, or the rather unexpected possibility that metamitron itself did select for metamitron-resistant biotypes bearing cross-resistance to atrazine, had become reality.

Amelioration of biodiversity impacts of genetically modified crops: predicting transient versus long-term effects

It has been suggested that genetically modified herbicide-tolerant crops may benefit biodiversity because spraying of crops may be delayed until later in the growing season, allowing weeds to grow during the early part of the year. This provides an enhanced resource for arthropods, and potentially benefits birds that feed on these. Thus, this technology could enhance biodiversity. Using a review of weed phenologies and a population model, we show that many weeds are unlikely to benefit because spraying is generally delayed insufficiently late in the season to allow most to set seed. The positive effects on biodiversity observed in trials lasting one or two seasons are thus likely to be transient. For one weed of particular significance (Chenopodium album, fat hen) we show that it is unlikely that the positive effects observed could be maintained by inputs of seed during other parts of the rotation. However, we find preliminary evidence that if spraying can be ceased earlier in the season, then a viable population of late-emerging weeds could be maintained. This strategy could benefit weeds in both genetically modified (GM) and non-GM crops, but would probably lead to reduced inputs in GM systems compared with conventional ones.

Photosynthetic electron transport inhibition by 2-substituted 4-alkyl-6-benzylamino-1,3,5-triazines with thylakoids from wild-type and atrazine-resistant Chenopodium album

The effect of 2-benzylamino-1,3,5-triazines on photosynthetic electron transport (PET) was measured with thylakoids isolated from atrazine-resistant, wild-type Chenopodium album, and spinach to find novel 1,3,5-triazine herbicides bearing a strong PET inhibition. The PET inhibition assay with Chenopodium (wild-type and resistant), yielded a resistance ratio (R/W = I50 (resistant)/I50 (wild-type)) of 324 for atrazine while for benzylamino-1,3,5-triazine derivatives of diamino-1,3,5-triazines a R/W of 11 to 160 was found. The compounds having a benzylamino group at one of the amino groups in the diamino-1,3,5-triazines have a resistant ratio down to one half to 1/30 of the atrazine value. The average resistance ratio of 21 benzylamino derivatives of monoamino-1,3,5-triazines was found to be about 4.0. The inhibition of 21 benzylamino-1,3,5-triazines assayed with atrazine-resistant Chenopodium thylakoids, indicated by pI50 (R)-values, correlated well with the PET inhibition pI50 (W) of wild-type thylakoids from Chenopodium.

Determination of Ascochyta caulina phytotoxins by high-performance anion exchange chromatography and pulsed amperometric detection

A simple and sensitive method has been developed for the rapid qualitative and quantitative analysis of the phytotoxins produced by Ascochyta caulina, a potential mycoherbicide for the biocontrol of Chenopodium album. Considering that the two main toxins produced by this fungus, namely ascaulitoxin and trans-4-amino-D-proline, and the third toxin, identified as 2,4,7-triamino-5-hydroxyoctandioic acid, have an amino acid nature, high-performance anion exchange chromatography with pulsed amperometric detection was the best method for their detection. The method was used to measure the toxin content in the culture filtrates of different strains of A. caulina. The developed method could be employed as a tool to select more virulent strains by determining the higher toxin producers, if in vitro toxin accumulation was related to pathogen virulence. The chemical characterisation of the third toxin purified from A. caulina culture filtrates is also reported.