Barbarea Vulgaris Research Articles

Evaluation of Trap Cropping for Control of Diamondback Moth (Lepidoptera: Plutellidae) in a Broccoli Production System.

Trap cropping, in which a trap crop is planted near a cash crop, has been used successfully for reducing pest damage in some agricultural systems. We used a meta-analysis of extensive data on two trap cropping systems, diamondback moth, Plutella xylostella (Linnaeus), exploiting cabbage and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) exploiting maize, to show that oviposition preference for, and high larval mortality on trap crops are important indicators of effectiveness of trap cropping systems. We then evaluated Indian mustard (Brassica juncea var. juncea L. Czern.) (Capparidales: Brassicaceae) and yellow rocket (Barbarea vulgaris W. T. Aiton) (Brassicales: Brassicaceae) as trap crops for protecting broccoli (Brassica oleracea var. italica Plenck) (Capparidales: Brassicaceae) against diamondback moth in Yuma, AZ, using planting configurations compatible with current practices for commercial production and without use of insecticides. In oviposition choice tests, both yellow rocket and Indian mustard were highly preferred over broccoli in the field. Furthermore, the number of larvae and pupae was significantly lower on yellow rocket and Indian mustard compared to broccoli, indicating relatively high mortality on these trap crops. Nevertheless, during the fall and spring growing seasons, no significant differences in the number of individuals on broccoli or proportion of broccoli crowns infested at harvest occurred between plots with trap crops relative to plots exclusively planted to broccoli. Thus, with the plant density and planting patterns used and without use of insecticides, there was no evidence that trap cropping was effective for reducing diamondback moth infestation of broccoli.

Evolution of Structural Diversity of Triterpenoids.

Plants have evolved to produce a blend of specialized metabolites that serve functional roles in plant adaptation. Among them, triterpenoids are one of the largest subclasses of such specialized metabolites, with more than 14,000 known structures. They play a role in plant defense and development and have potential applications within food and pharma. Triterpenoids are cyclized from oxidized squalene precursors by oxidosqualene cyclases, creating more than 100 different cyclical triterpene scaffolds. This limited number of scaffolds is the first step towards creating the vast structural diversity of triterpenoids followed by extensive diversification, in particular, by oxygenation and glycosylation. Gene duplication, divergence, and selection are major forces that drive triterpenoid structural diversification. The triterpenoid biosynthetic genes can be organized in non-homologous gene clusters, such as in Avena spp., Cucurbitaceae and Solanum spp., or scattered along plant chromosomes as in Barbarea vulgaris. Paralogous genes organized as tandem repeats reflect the extended gene duplication activities in the evolutionary history of the triterpenoid saponin pathways, as seen in B. vulgaris. We review and discuss examples of convergent and divergent evolution in triterpenoid biosynthesis, and the apparent mechanisms occurring in plants that drive their increasing structural diversity within and across species. Using B. vulgaris’ saponins as examples, we discuss the impact a single structural modification can have on the structure of a triterpenoid and how this affect its biological properties. These examples provide insight into how plants continuously evolve their specialized metabolome, opening the way to study uncharacterized triterpenoid biosynthetic pathways.

Aminorex identified in horse urine following consumption of Barbarea vulgaris; a preliminary report

BackgroundAminorex, (RS)-5- Phenyl-4,5-dihydro-1,3-oxazol-2-amine, is an amphetamine-like anorectic and in the United States a Drug Enforcement Administration [DEA] Schedule 1 controlled substance. Aminorex in horse urine is usually present as a metabolite of Levamisole, an equine anthelmintic and immune stimulant. Recently, Aminorex identifications have been reported in horse urine with no history or evidence of Levamisole administration. Analysis of the urine samples suggested a botanical source, directing attention to the Brassicaceae plant family, with their contained GlucoBarbarin and Barbarin as possible sources of Aminorex. Since horsepersons face up to a 1 year suspension and a $10,000.00 fine for an Aminorex identification, the existence of natural sources of Aminorex precursors in equine feedstuffs is of importance to both individual horsepersons and the industry worldwide.ResultsTesting the hypothesis that Brassicaceae plants could give rise to Aminorex identifications in equine urine we botanically identified and harvested flowering Kentucky Barbarea vulgaris, (“Yellow Rocket”) in May 2018 in Kentucky and administered the plant orally to two horses. Analysis of post-administration urine samples yielded Aminorex, showing that consumption of Kentucky Barbarea vulgaris can give rise to Aminorex identifications in equine urine.ConclusionsAminorex has been identified in post administration urine samples from horses fed freshly harvested flowering Kentucky Barbarea vulgaris, colloquially “Yellow Rocket”. These identifications are consistent with occasional low concentration identifications of Aminorex in equine samples submitted for drug testing. The source of these Aminorex identifications is believed to be the chemically related Barbarin, found as its precursor GlucoBarbarin in Kentucky Barbarea vulgaris and related Brassicaceae plants worldwide.

Role of Saponins in Plant Defense Against Specialist Herbivores.

The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae) is a very destructive crucifer-specialized pest that has resulted in significant crop losses worldwide. DBM is well attracted to glucosinolates (which act as fingerprints and essential for herbivores in host plant recognition) containing crucifers such as wintercress, Barbarea vulgaris (Brassicaceae) despite poor larval survival on it due to high-to-low concentration of saponins and generally to other plants in the genus Barbarea. B. vulgaris build up resistance against DBM and other herbivorous insects using glucosinulates which are used in plant defense. Aside glucosinolates, Barbarea genus also contains triterpenoid saponins, which are toxic to insects and act as feeding deterrents for plant specialist herbivores (such as DBM). Previous studies have found interesting relationship between the host plant and secondary metabolite contents, which indicate that attraction or resistance to specialist herbivore DBM, is due to higher concentrations of glucosinolates and saponins in younger leaves in contrast to the older leaves of Barbarea genus. As a response to this phenomenon, herbivores as DBM has developed a strategy of defense against these plant biochemicals. Because there is a lack of full knowledge in understanding bioactive molecules (such as saponins) role in plant defense against plant herbivores. Thus, in this review, we discuss the role of secondary plant metabolites in plant defense mechanisms against the specialist herbivores. In the future, trials by plant breeders could aim at transferring these bioactive molecules against herbivore to cash crops.

A high-density genetic map and QTL mapping of leaf traits and glucosinolates in Barbarea vulgaris

BackgroundBarbarea vulgaris is a wild cruciferous plant and include two distinct types: the G- and P-types named after their glabrous and pubescent leaves, respectively. The types differ significantly in resistance to a range of insects and diseases as well as glucosinolates and other chemical defenses. A high-density linkage map was needed for further progress to be made in the molecular research of this plant.ResultsWe performed restriction site-associated DNA sequencing (RAD-Seq) on an F2 population generated from G- and P-type B. vulgaris. A total of 1545 SNP markers were mapped and ordered in eight linkage groups, which represents the highest density linkage map to date for the crucifer tribe Cardamineae. A total of 722 previously published genome contigs (50.2 Mb, 30% of the total length) can be anchored to this high density genetic map, an improvement compared to a previously published map (431 anchored contigs, 38.7 Mb, 23% of the assembly genome). Most of these (572 contigs, 31.2 Mb) were newly anchored to the map, representing a significant improvement. On the basis of the present high-density genetic map, 37 QTL were detected for eleven traits, each QTL explaining 2.9–71.3% of the phenotype variation. QTL of glucosinolates, leaf size and color traits were in most cases overlapping, possibly implying a functional connection.ConclusionsThis high-density linkage map and the QTL obtained in this study will be useful for further understanding of the genetic of the B. vulgaris and molecular basis of these traits, many of which are shared in the related crop watercress.

The cytochrome P450 CYP72A552 is key to production of hederagenin-based saponins that mediate plant defense against herbivores.

Plants continuously evolve new defense compounds. One class of such compounds is triterpenoid saponins. A few species in the Barbarea genus produce saponins as the only ones in the large crucifer family. However, the molecular mechanism behind saponin biosynthesis and their role in plant defense remains unclear. We used pathway reconstitution in planta, enzymatic production of saponins invitro, insect feeding assays, and bioinformatics to identify a missing gene involved in saponin biosynthesis and saponin-based herbivore defense. A tandem repeat of eight CYP72A cytochromes P450 colocalise with a quantitative trait locus (QTL) for saponin accumulation and flea beetle resistance in Barbarea vulgaris. We found that CYP72A552 oxidises oleanolic acid at position C-23 to hederagenin. In vitro-produced hederagenin monoglucosides reduced larval feeding by up to 90% and caused 75% larval mortality of the major crucifer pest diamondback moth and the tobacco hornworm. Sequence analysis indicated that CYP72A552 evolved through gene duplication and has been under strong selection pressure. In conclusion, CYP72A552 has evolved to catalyse the formation of hederagenin-based saponins that mediate plant defense against herbivores. Our study highlights the evolution of chemical novelties by gene duplication and selection for enzyme innovations, and the importance of chemical modification in plant defense evolution.

Host preference variation cannot explain microhabitat differentiation among sympatric Pieris napi and Pieris rapae butterflies

1. Often, closely related insect species feed on different host plant species, and the tremendous diversity of phytophagous insects is therefore attributed to host plant‐driven speciation. However, for most taxa, host use information comes from field observations of egg‐laying females or feeding caterpillars, which means that the underlying reason for a particular host‐affiliation is not easily determined.2. Therefore, it is often unclear whether an insect feeds on a certain host because it prefers that plant to alternative hosts, or because the host distribution overlaps with the habitat requirements of the insect.3. We ask to what extent a divergent host use in the field mirrors the host plant preferences of two closely related butterflies, Pieris napi and Pieris rapae (Pieridae). In nature, P. napi typically occurs in moister habitats than P. rapae.4. We scanned several microhabitats at a field site in Southern Sweden during multiple years, and collected Pieris eggs from three different plants, Cardamine pratensis (wet meadows), Barbarea vulgaris (drier micro‐habitats) and Alliaria petiolata (intermediate areas).5. As predicted, P. rapae eggs were more common than P. napi eggs on B. vulgaris, whereas all of the 358 individuals collected from C. pratensis were P. napi, indicating a divergence in host use between the Pieris species. However, under controlled laboratory conditions, both species had virtually identical oviposition preferences, laying eggs on all three plants, notably P. rapae also laying eggs on C. pratensis, indicating that habitat use, not plant preference, drives host plant use in nature.

Trap Crops and Insectary Plants in the Order Brassicales

Abstract This paper reviews the most important cases of trap crops and insectary plants in the order Brassicales. Most trap crops in the order Brassicales target insects that are specialist in plants belonging to this order, such as the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), the pollen beetle, Meligethes aeneus Fabricius (Coleoptera: Nitidulidae), and flea beetles in the genera Phyllotreta and Psylliodes (Coleoptera: Chrysomelidae). In most cases, the mode of action of these trap crops is the preferential attraction of the insect pest for the trap crop located next to the main crop. With one exception, these trap crops in the order Brassicales have been used with brassicaceous crops. Insectary plants in the order Brassicales attract a wide variety of natural enemies, but most studies focus on their effect on aphidofagous hoverflies and parasitoids. The parasitoids benefiting from insectary plants in the order Brassicales target insects pests ranging from specialists, such as P. xylostella, to highly polyfagous, such as the stink bugs Euschistus conspersus Uhler and Thyanta pallidovirens Stål (Hemiptera: Pentatomidae). In the order Brassicales, the three most common trap crops are Indian mustard, Brassica juncea (L.) Czern, Chinese cabbage, Brassica rapa L., and yellow rocket, Barbarea vulgaris R. Br., while the three most common insectary plants are sweet alyssum, Lobularia maritima (L.) Desv., white mustard, Sinapis alba L, and B. vulgaris. Except for Tropaeolum majus L. (Tropaeolaceae) and Capparis decidua (Forssk.) Edgew. (Capparaceae), the tested trap crops and insectary plants in the order Brassicales belong to the family Brassicaceae.

The Role of the Glucosinolate-Myrosinase System in Mediating Greater Resistance of Barbarea verna than B. vulgaris to Mamestra brassicae Larvae

We investigated the influences of two structurally similar glucosinolates, phenethylglucosinolate (gluconasturtiin, NAS) and its (S)-2-hydroxyl derivative glucobarbarin (BAR), as well as their hydrolysis products on larvae of the generalist Mamestra brassicae (Lepidoptera: Noctuidae). Previous results suggested a higher defensive activity of BAR than NAS based on resistance toward M. brassicae larvae of natural plant genotypes of Barbarea vulgaris R. Br. (Brassicaceae) dominated by BAR. In the present study, the hypothesis of a higher defensive activity of BAR than NAS was tested by comparing two Barbarea species similarly dominated either by BAR or by NAS and by testing effects of isolated BAR and NAS on larval survival and feeding preferences. Larvae reared on leaf disks of B. verna (Mill.) Asch. had a lower survival than those reared on B. vulgaris P- and G-chemotypes. Leaves of B. verna were dominated by NAS, whereas B. vulgaris chemotypes were dominated by BAR or its epimer. In addition, B. verna leaves showed a threefold higher activity of the glucosinolate-activating myrosinase enzymes. The main product of NAS from breakdown by endogenous enzymes including myrosinases ("autolysis") in B. verna leaves was phenethyl isothiocyanate, while the main products of BAR in autolyzed B. vulgaris leaves were a cyclized isothiocyanate product, namely an oxazolidine-2-thione, and a downstream metabolite, an oxazolidin-2-one. The glucosinolates BAR and NAS were isolated and offered to larvae on disks of cabbage. Both glucosinolates exerted similar negative effects on larval survival but effects of NAS tended to be more detrimental. Low concentrations of BAR, but not of NAS, stimulated larval feeding, whereas high BAR concentrations acted deterrent. NAS only tended to be deterrent at the highest concentration, but the difference was not significant. Recoveries of NAS and BAR on cabbage leaf disks were similar, and when hydrolyzed by mechanical leaf damage, the same isothiocyanate-type products as in Barbarea plants were formed with further conversion of BAR to cyclic products, (R)-5-phenyloxazolidine-2-thione [(R)-barbarin] and (R)-5-phenyloxazolidin-2-one [(R)-resedine]. We conclude that a previously proposed generally higher defensive activity of BAR than NAS to M. brassicae larvae could not be confirmed. Indeed, the higher resistance of NAS-containing B. verna plants may be due to a combined effect of rather high concentrations of NAS and a relatively high myrosinase activity or other plant traits not investigated yet.

Different herbivore responses to two co-occurring chemotypes of the wild crucifer Barbarea vulgaris

According to coevolution theory, plant chemical defences are continually evolving in response to selection by herbivores. Unique to the Brassicales, a few species in the Barbarea genus produce triterpenoid saponins that are highly deterrent to some specialist insect herbivores. One species, B. vulgaris, has diverged into two chemotypes, the G- and P-type, of which the P-type seems to have lost the saponin-based insect resistance by producing different saponin structures; it also produces different glucosinolates and other potential defence traits. Here, we examined the preference and performance of a larger set of specialist and generalist herbivores on the two plant types, including three generalist mollusc (Arion vulgaris, Deroceras sp., Cepaea sp.) as well as three specialist (Phaedon cochleariae, Athalia rosae, Pieris napi oleraceae) and two generalist (Mamestra brassicae, Myzus persicae) insect herbivores. Five out of six herbivore species preferred leaves of the P-type for feeding, and most of them also survived and/or grew better on the P-type, or preferred it for oviposition. In contrast, larvae of M. brassicae showed no preference and performed equally well on the two plant types; the leaf beetle P. cochleariae preferred the G-type for oviposition, which was, however, not reflecting larval performance. Overall, the defences of the P-type against herbivores seem not to be as effective as those of the G-type, which is surprising given its large geographical distribution, overlapping with that of the G-type in Scandinavia and Finland. This suggests that additional ecological interactions determine the success of the two chemotypes.

Glucosinolate turnover in Brassicales species to an oxazolidin-2-one, formed via the 2-thione and without formation of thioamide

Glucosinolates are found in plants of the order Brassicales and hydrolyzed to different breakdown products, particularly after tissue damage. In Barbarea vulgaris R.Br. (Brassicaceae), the dominant glucosinolate in the investigated “G-type” is glucobarbarin, (S)-2-hydroxy-2-phenylethylglucosinolate. Formation of the nitrile from glucobarbarin was observed in vitro, while a previously suggested thioamide (synonym thionamide) was not confirmed. Resedine (5-phenyl-1,3-oxazolidin-2-one) was detected after glucobarbarin hydrolysis in crushed B. vulgaris leaves and siliques, but not in intact parts. The abundance increased for several hours after completion of hydrolysis. The corresponding 1,3-oxazolidine-2-thione (OAT), with the common name barbarin, was also formed, and appeared to be the precursor of resedine. Addition of each of two non-endogenous OATs, (S)-5-ethyl-5-methylOAT and (R)-5-vinylOAT (R-goitrin), to a leaf homogenate resulted in formation of the corresponding 1,3-oxazolidin-2-ones (OAOs), confirming the metabolic connection of OAT to OAO. Formation of OAOs was inhibited by prior brief heating of the homogenate, suggesting enzyme involvement. We suggest the conversion of OATs to OAOs to be catalyzed by an enzyme (“oxazolidinethionase”) responsible for turnover of OAT formed in intact plants. Resedine had been reported as an alkaloid from another species - Reseda luteola L. (Resedaceae) - naturally containing the glucosinolate glucobarbarin. However, resedine was not detected in intact R. luteola plants, but formed after tissue damage. The formation of resedine in two families suggests a broad distribution of putative OATases in the Brassicales; potentially involved in glucosinolate turnover that needs myrosinase activity as the committed step. In agreement with the proposed function of OATase, several candidate genes for myrosinases in glucosinolate turnover in intact plants were discovered in the B. vulgaris genome. We also suggest that biotechnological conversion of OATs to OAOs might improve the nutritional value of Brassicales protein. HPLC-MS/MS methods for detection of these glucobarbarin products are described.

Resistance and susceptibility to powdery mildew, root-knot nematode, and western flower thrips in two types of winter cress (Brassicaceae)

Two types of Barbarea vulgaris R. Br. (Brassicaceae) were tested to compare their resistance and susceptibility to powdery mildew, Erysiphe cruciferarum Opiz ex L. Junell (Erysiphales: Erysiphaceae), root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwoodi (Tylenchida: Heteroderidae), and western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). In experiments conducted in the greenhouse, the percentage of plants showing powdery mildew symptoms ranged from 54.2 to 83.3% in P-type B. vulgaris plants and from 0 to 20.8% in G-type B. vulgaris plants. In plants infected by powdery mildew, the percentage of leaves affected was higher in P-type than in G-type plants, ranging from 11.8 to 21.1% in P-type plants, and from 0 to 0.36% in G-type plants. Infection by powdery mildew was more likely to occur on the leaves of largest diameter. Root galling showed that G- and P-type plants were equally attacked by root-knot nematode, but the multiplication rate of the nematode was 4.1–7.6 times higher in P-type than in G-type plants. Significantly more leaves per plant were damaged by western flower thrips in P-type (73.1–88.3% of leaves affected) than in G-type plants (2.1–2.9% of leaves affected). The total numbers of adult and immature thrips found per plant on P-type plants were, respectively, 29.9 and 2.5, while on G-type plants less than 0.3 adult and immature thrips were found per plant. This study indicates that G-type B. vulgaris could be a source of resistance to powdery mildew and western flower thrips.

A tandem array of UDP-glycosyltransferases from the UGT73C subfamily glycosylate sapogenins, forming a spectrum of mono- and bisdesmosidic saponins.

This study identifies six UGT73Cs all able to glucosylate sapogenins at positions 3 and/or 28 which demonstrates that B. vulgaris has a much richer arsenal of UGTs involved in saponin biosynthesis than initially anticipated. The wild cruciferous plant Barbarea vulgaris is resistant to some insects due to accumulation of two monodesmosidic triterpenoid saponins, oleanolic acid 3-O-β-cellobioside and hederagenin 3-O-β-cellobioside. Insect resistance depends on the structure of the sapogenin aglycone and the glycosylation pattern. The B. vulgaris saponin profile is complex with at least 49 saponin-like metabolites, derived from eight sapogenins and including up to five monosaccharide units. Two B. vulgaris UDP-glycosyltransferases, UGT73C11 and UGT73C13, O-glucosylate sapogenins at positions 3 and 28, forming mainly 3-O-β-D-glucosides. The aim of this study was to identify UGTs responsible for the diverse saponin oligoglycoside moieties observed in B. vulgaris. Twenty UGT genes from the insect resistant genotype were selected and heterologously expressed in Nicotiana benthamiana and/or Escherichia coli. The extracts were screened for their ability to glycosylate sapogenins (oleanolic acid, hederagenin), the hormone 24-epibrassinolide and sapogenin monoglucosides (hederagenin and oleanolic acid 3-O-β-D-glucosides). Six UGTs from the UGT73C subfamily were able to glucosylate both sapogenins and both monoglucosides at positions 3 and/or 28. Some UGTs formed bisdesmosidic saponins efficiently. At least four UGT73C genes were localized in a tandem array with UGT73C11 and possibly UGT73C13. This organization most likely reflects duplication events followed by sub- and neofunctionalization. Indeed, signs of positive selection on several amino acid sites were identified and modelled to be localized on the UGT protein surface. This tandem array is proposed to initiate higher order bisdesmosidic glycosylation of B. vulgaris saponins, leading to the recently discovered saponin structural diversity, however, not directly to known cellobiosidic saponins.

Biosynthesis of Glycyrrhetinic Acid-3-O-monoglucose Using Glycosyltransferase UGT73C11 from Barbarea vulgaris

Glycyrrhetinic acid (GA) is the pentacyclic triterpenoid hydrophobic aglycone with many pharmacological effects and biological activities. Glycosylation is often used to improve the aglycone’s properties such as solubility, stability, and pharmacological potency. UDP-glycosyltransferases (UGTs) are the main enzymes to catalyze this conversion via transferring glycosyl moiety to corresponding acceptor substrates in nature. However, a glycosyltransferase which can transfer glucose to GA has not been reported yet. The glycosyltransferase UGT73C11 from the plant Barbarea vulgaris was reported with the glycosylation function to compounds which are similar to GA in chemical structure. In this study, UGT73C11 was selected to express functionally in Escherichia coli and purified as the biocatalyst for the glycosylation of GA. As a result, the recombinant UGT73C11 catalyzed UDP-glucose and GA to produce a new compound GA-3-O-monoglucose. The product GA-3-O-monoglucose was characterized by HPLC and LC–ESI-MS spectr...

The genome sequence of Barbarea vulgaris facilitates the study of ecological biochemistry

The genus Barbarea has emerged as a model for evolution and ecology of plant defense compounds, due to its unusual glucosinolate profile and production of saponins, unique to the Brassicaceae. One species, B. vulgaris, includes two ‘types’, G-type and P-type that differ in trichome density, and their glucosinolate and saponin profiles. A key difference is the stereochemistry of hydroxylation of their common phenethylglucosinolate backbone, leading to epimeric glucobarbarins. Here we report a draft genome sequence of the G-type, and re-sequencing of the P-type for comparison. This enables us to identify candidate genes underlying glucosinolate diversity, trichome density, and study the genetics of biochemical variation for glucosinolate and saponins. B. vulgaris is resistant to the diamondback moth, and may be exploited for “dead-end” trap cropping where glucosinolates stimulate oviposition and saponins deter larvae to the extent that they die. The B. vulgaris genome will promote the study of mechanisms in ecological biochemistry to benefit crop resistance breeding.

Screening for Triterpenoid Saponins in Plants Using Hyphenated Analytical Platforms.

Recently the number of studies investigating triterpenoid saponins has drastically increased due to their diverse and potentially attractive biological activities. Currently the literature contains chemical structures of few hundreds of triterpenoid saponins of plant and animal origin. Triterpenoid saponins consist of a triterpene aglycone with one or more sugar moieties attached to it. However, due to similar physico-chemical properties, isolation and identification of a large diversity of triterpenoid saponins remain challenging. This study demonstrates a methodology to screen saponins using hyphenated analytical platforms, GC-MS, LC-MS/MS, and LC-SPE-NMR/MS, in the example of two different phenotypes of the model plant Barbarea vulgaris (winter cress), glabrous (G) and pubescent (P) type that are known to differ by their insect resistance. The proposed methodology allows for detailed comparison of saponin profiles from intact plant extracts as well as saponin aglycone profiles from hydrolysed samples. Continuously measured 1D proton NMR data during LC separation along with mass spectrometry data revealed significant differences, including contents of saponins, types of aglycones and numbers of sugar moieties attached to the aglycone. A total of 49 peaks were tentatively identified as saponins from both plants; they are derived from eight types of aglycones and with 2–5 sugar moieties. Identification of two previously known insect-deterrent saponins, hederagenin cellobioside and oleanolic acid cellobioside, demonstrated the applicability of the methodology for relatively rapid screening of bioactive compounds.

Can flowering Barbarea spp. (Brassicaceae) be used simultaneously as a trap crop and in conservation biological control?

Barbarea vulgaris R. Br. and B. verna (Mill.) Asch (Brassicaceae) have been proposed as trap crops for the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae). In bloom, these plants could also be used to attract beneficial insects. In this study, we tested the attractiveness of flowering Barbarea to P. xylostella and to two of its parasitoids, Diadegma insulare Cresson (Hymenoptera: Ichneumonidae) and Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae). We also tested whether the presence of flowering Barbarea planted in the field border could affect densities of 10 insect pests and two beneficial coccinellids in adjacent cauliflower plants. Flowering Barbarea did not change the densities of insects found in adjacent cauliflower, except for Eurydema ornata L. (Hemiptera: Pentatomidae), which densities on cauliflower were reduced by flowering B. vulgaris. Coccinellids were more abundant on flowering Barbarea than on cauliflower plants. Chrysomelids were also more abundant on flowering Barbarea than on cauliflower plants, while hemipteran and lepidopteran pests were often more abundant on cauliflower than on Barbarea plants. In plots with flowering B. vulgaris, P. xylostella pupae suffered 1.7 and 4.0 times more parasitism by D. insulare and D. collaris, respectively, than in plots without flowering B. vulgaris. Flowering reduced the attractiveness of Barbarea to P. xylostella, making it lose its effectiveness as a trap crop. However, being biennial, Barbarea could be used as a trap crop for P. xylostella the first year, and to lower the populations of E. ornata and increase parasitism of P. xylostella when it flowers the second year.

Glucosinolate diversity within a phylogenetic framework of the tribe Cardamineae (Brassicaceae) unraveled with HPLC-MS/MS and NMR-based analytical distinction of 70 desulfoglucosinolates

As a basis for future investigations of evolutionary trajectories and biosynthetic mechanisms underlying variations in glucosinolate structures, we screened members of the crucifer tribe Cardamineae by HPLC-MS/MS, isolated and identified glucosinolates by NMR, searched the literature for previous data for the tribe, and collected HPLC-MS/MS data for nearly all glucosinolates known from the tribe as well as some related structures (70 in total). This is a considerable proportion of the approximately 142 currently documented natural glucosinolates. Calibration with authentic references allowed distinction (or elucidation) of isomers in many cases, such as distinction of β-hydroxyls, methylthios, methylsulfinyls and methylsulfonyls. A mechanism for fragmentation of secondary β-hydroxyls in MS was elucidated, and two novel glucosinolates were discovered: 2-hydroxy-3-methylpentylglucosinolate in roots of Cardamine pratensis and 2-hydroxy-8-(methylsulfinyl)octylglucosinolate in seeds of Rorippa amphibia. A large number of glucosinolates (ca. 54 with high structural certainty and a further 28 or more suggested from tandem MS), representing a wide structural variation, is documented from the tribe. This included glucosinolates apparently derived from Met, Phe, Trp, Val/Leu, Ile and higher homologues. Normal side chain elongation and side chain decoration by oxidation or methylation was observed, as well as rare abnormal side chain decoration (hydroxylation of aliphatics at the δ rather than β-position). Some species had diverse profiles, e.g. R. amphibia and C. pratensis (19 and 16 individual glucosinolates, respectively), comparable to total diversity in literature reports of Armoracia rusticana (17?), Barbarea vulgaris (20–24), and Rorippa indica (>20?). The ancestor or the tribe would appear to have used Trp, Met, and homoPhe as glucosinolate precursor amino acids, and to exhibit oxidation of thio to sulfinyl, formation of alkenyls, β-hydroxylation of aliphatic chains and hydroxylation and methylation of indole glucosinolates. Two hotspots of apparent biochemical innovation and loss were identified: C. pratensis and the genus Barbarea. Diversity in other species mainly included structures also known from other crucifers. In addition to a role of gene duplication, two contrasting genetic/biochemical mechanisms for evolution of such combined diversity and redundancy are discussed: (i) involvement of widespread genes with expression varying during evolution, and (ii) mutational changes in substrate specificities of CYP79F and GS-OH enzymes.

A hybridisation barrier between two evolutionary lineages of Barbarea vulgaris (Brassicaceae) that differ in biotic resistances

Hybridisation barriers are likely to evolve during allopatric separation of populations, in parallel with divergent adaptation to different conditions in the two ranges. If the populations secondarily come into contact, limited interbreeding between them may affect the subsequent spread of the two lineages and their adaptations in the region of sympatry. Barbarea vulgaris include two genetically divergent lineages that differ in secondary metabolites and resistances to insects and a pathogen. The two plant types grow in different Eurasian ranges but co-occur in Denmark and neighbouring countries, posing the question why they have not merged and the resistances spread from one type into the range of the other. Here, we tested whether a hybridisation barrier contribute to this. Different proportions of plants of the two types were placed in net tents and pollinated by flies, and paternity of the resulting seeds determined with genetic markers. Lower proportions of fruits and seeds developed successfully in mixtures with higher proportions of heterotypic plants (i.e. of the other plant type). When combined with results on offspring paternity in a statistical analysis, we found that heterotypic pollen was much less successful in fertilizing embryos and that heterotypic seeds survived less frequently than the contypic. Mature F1 hybrids in addition produced lower proportions of mature pollen. The two B. vulgaris plant types are thus separated by substantial prezygotic and postzygotic barriers, as strong as reported for crosses between closely related but taxonomically recognised plant species. This may explain why the two B. vulgaris types have not merged in sympatry and why genes for insect-resistance have not introgressed to any extent from one to the other.

Butterflies and plants: preference/performance studies in relation to plant size and the use of intact plants vs. cuttings

AbstractPlants have evolved a number of defences to ameliorate herbivore attacks including chemicals induced by mechanical wounding. Such changes in plant chemical composition are potential confounding factors in experiments on plant–insect interactions, which often present cuttings of potential host plants to phytophagous insects. In particular, this could affect studies of female egg‐laying preference and larval performance, because the same plant chemicals that deter certain generalist insects can elevate attacks from more specialized insects. Furthermore, plant cuttings are by definition smaller than intact plants, and any female host size preference could thus affect experiments using plant cuttings. We first assessed female preference and larval performance of a specialist herbivore, Pieris napi (L.) (Lepidoptera: Pieridae, Pierini), confronted with either intact plants or leaf‐cuttings of four Brassicaceae host plants, Alliaria petiolata (Bieb.) Cavara & Grande, Barbarea vulgaris (L.) WT Aiton, Berteroa incana (L.) DC., and Brassica napus (L.). Egg and larval survival did not differ between intact plants and leaf‐cuttings, whereas larval growth was slightly, but significantly, faster on leaf‐cuttings. Females, however, significantly preferred to lay eggs on intact plants of all four hosts, although the preference hierarchy for the intact plants was largely mirrored by that for leaf‐cuttings. We then tested the female preference for different size‐classes of intact B. napus plants. Small individuals received more eggs than larger individuals, and follow‐up experiments showed that this difference was largely generated by a strong female preference for cotyledon leaves; there was no significant difference in female preference for large and small individuals when both carried cotyledons, and females landing on cotyledons were more likely to oviposit compared to when landing on a true leaf. Our study concludes that plant cuttings can serve as adequate proxies for live plants for preference/performance studies, but that experimentalists should be aware of the variation imposed both by plant handling and plant phenology for female oviposition preference.