Nigra Plants Research Articles

Performance of poplars and willow grown on soil under wastewater irrigation during the first 2 years of establishment.

Recycling wastewaters as irrigation and fertilization of tree species is a market-driven action for purpose-grown timber plantations that promotes the circular economy. A greenhouse experiment was carried out to investigate the performance of poplar clones (Populus alba L. "20/45", P. nigra L. "62/154", and P. euramericana (Dode) Guinier "92/40") and willow (Salix excelsa S.G. Gmel) grown on soils under tap water irrigation (TWI) or wastewater irrigation (WWI) during the first 2 years of establishment. Results showed that at 2 years after planting, poplars and willow exhibited significantly greater performance when grown in WWI versus TWI (P < 0.05). Likewise, phytoremediation of nutrients along with some heavy metals increased in plant organs of WWI-grown plants relative to their TWI counterparts (P < 0.05). After 2 years of growth and under both conditions (TWI and WWI), P. nigra plants showed the greatest growth and biomass; however, leaf area was the largest for P. alba and P. euramericana plants. Also, P. nigra plants had the highest total contents of copper (Cu) and manganese (Mn), P. alba had the most zinc (Zn), and differences for iron (Fe) were negligible across species. In contrast, total contents of nickel (Ni) and chromium (Cr) were higher for S. excelsa, P. nigra, and P. alba plants, while the lowest values were measured in P. euramericana plants. Across all species and soil treatments, the translocation factor (TF) was greater than 1 for Mn, Cu, and Zn, indicating phytoextraction and phytoaccumulation of these elements into leaves and stems, while TF was less than 1 for Fe, lead (Pb), Ni, and Cr, resulting in phytoremediation of these elements as phytostabilization. Differences in tolerance index (TI) values were negligible across species, and TI was greater than 100% after 2 years of growth, indicating that all four species are suitable for phytoremediation applications with urban wastewaters having similar heavy metal concentrations as in the present study. Nevertheless, given the combination of enhanced growth, biomass, and heavy metal accumulation (Mn, Cu, Cr, and Ni), P. nigra plants exhibited the greatest phytoremediation potential of four tested species.

New Ophiostoma species associated with Dryocoetes himalayensis and decline of Juglans regia in Czechia

AbstractA new ophiostomatoid fungus involved in the decline of walnuts was discovered in Czechia. The fungus was isolated from necrotic wood surrounding the larval galleries of Dryocoetes himalayensis, the alien bark beetle attacking walnut trees. This insect species is rather unique within hardwood-associated bark beetle species for its aggressiveness and ability to attack apparently healthy trees. The isolated fungus, associated with an exotic insect vector is described as a new species, Ophiostoma juglandis sp. nov., based on its unique morphology and phylogenetic position. The pathogenicity tests confirmed the aggressiveness of the species to both Juglans regia and J. nigra plants, manifested by formation of extensive bleeding and necrotic lesions. The symbiotic relationship between O. juglandis and D. himalayensis is expected due to massive presence of the fungal spores on surface of adult beetles in pits forming the elytral striae. In the case of hardwood-associated ophiostomatoid fungal species, phytopathogenicity is very rarely observed. The described species is exceptional in this ability, which corresponds to the aggressive behaviour of its vector. The role of the fungus in walnut tree mortality caused by D. himalayensis is discussed.

SRAP markers for characterization of the genetic diversity and differentiation of Pinus nigra populations in protected forested areas in Bulgaria, Greece, and Cyprus

The present study aimed to evaluate the genetic diversity and differentiation of Pinus nigra Arnold, the European black pine, populations located in protected forested areas in three countries from the Balkan and Mediterranean region: Bulgaria, Greece, and Cyprus. Totally, 175 DNA samples from P. nigra plants collected from eight populations in these countries were analyzed using three SRAP primer pairs. The applied SRAP markers demonstrated high-resolution power, resulting in the identification of an average of 215 ± 67 polymorphic loci per SRAP primer pair. The analysis of molecular variance (AMOVA) showed that 82% of the observed variation was due to intra-population variation, while 18% was due to inter-population variation. The overall analysis of the population structure suggested low (Fst ≤ 0.01) intra-country differentiation for the populations from Bulgaria and Cyprus and moderate (0.15 ≤ Fst ≤ 0.17) inter-country differentiation. On the contrary, high differentiation between the populations (0.06 ≤ Fst ≤ 0.20) and complex genetic structure were characteristic of the three populations from Greece, relatively closely located in the area of the Pindos National Park. Analysis of the population structure also revealed that one of the Pindos populations belonged to the cluster of Bulgarian populations (Fst ≤ 0.01), showing moderate (Fst ≤ 0.11) to high (Fst ≤ 0.20) genetic differentiation from the other analyzed Pindos populations. The further use of SRAP markers for mapping the genetic diversity among P. nigra populations and identification of local populations diverted from the overall phylogeography-driven pattern in the studied region are discussed.

Alkaline soil primes the recovery from drought in Populus nigra plants through physiological and chemical adjustments

Perennial plants are frequently exposed to severe and prolonged drought, and when the balance between water transport and transpirational demand is compromised trees are in danger of embolism formation. To maintain the physiological balance, plants can rely on mechanisms to quickly recover the lost xylem hydraulic capacity and reduce the prolonged impact on photosynthetic activity upon rehydration. Among factors helpful for plants to sustain acclimation and adaptation responses to drought and promote recovery, maintaining an optimal nutritional status is crucial for plant survival.This study aimed to investigate the physiological and biochemical responses under drought and recovery of Populus nigra plants grown in soil with impaired nutrient bioavailability obtained by adding calcium oxide (CaO) to the substrate. Although the CaO treatment did not affect plant growth, in well-watered conditions, treated poplars displayed an impaired inorganic ions profile in tissues. Under drought, although CaO-treated and untreated plants showed similar physiological responses, the former closed the stomata earlier. During water stress relief, the CaO-treated poplars exhibited a faster stomatal opening and a higher capacity to restore xylem hydraulic conductivity compared to not-treated plants, probably due to the higher osmolyte accumulation during drought. The content of some inorganic ions (e.g, Ca2+ and Cl−) was also higher in the xylem sap collected from stressed CaO-treated plants, thus contributing to increase the osmotic gradient necessary for the recovery. Taken together, our results suggest that CaO treatment promotes a faster and more efficient plant recovery after drought due to a modulation of ions homeostasis.

Insect exuviae as soil amendment affect flower reflectance and increase flower production and plant volatile emission.

Soil composition and herbivory are two environmental factors that can affect plant traits including flower traits, thus potentially affecting plant-pollinator interactions. Importantly, soil composition and herbivory may interact in these effects, with consequences for plant fitness. We assessed the main effects of aboveground insect herbivory and soil amendment with exuviae of three different insect species on visual and olfactory traits of Brassica nigra plants, including interactive effects. We combined various methodological approaches including gas chromatography/mass spectrometry, spectroscopy and machine learning to evaluate changes in flower morphology, colour and the emission of volatile organic compounds (VOCs). Soil amended with insect exuviae increased the total number of flowers per plant and VOC emission, whereas herbivory reduced petal area and VOC emission. Soil amendment and herbivory interacted in their effect on the floral reflectance spectrum of the base part of petals and the emission of 10 VOCs. These findings demonstrate the effects of insect exuviae as soil amendment on plant traits involved in reproduction, with a potential for enhanced reproductive success by increasing the strength of signals attracting pollinators and by mitigating the negative effects of herbivory.

Amending soil with insect exuviae improves herbivore tolerance, pollinator attraction and seed yield of Brassica nigra plants

To promote circularity in agriculture, the residual –streams from the production of insects as feed and food, such as insect exuviae (moulted skins), can be a sustainable novel organic soil amendment for crop production. Organic soil amendments can influence soil composition by providing nutrients and stimulating the growth of beneficial microorganisms. Soil composition significantly impacts plant growth and resistance against herbivores. However, little is known about the effect of soil composition on flower visitors and seed production. Here, black soldier fly (BSF; Hermetia illucens) exuviae was added to soil to investigate the effects on plant growth, plant resistance against two insect herbivores, and the consequences for attraction of pollinators and seed yield. Brassica nigra seeds were sown in field soil or in field soil mixed with powdered BSF exuviae. Three-week-old plants and the soil of each pot were planted in a common garden. The effects on vegetative and flower traits, interactions with flower visitors and seed yield were quantified. In addition, the performance of the leaf-chewing larvae of Pieris brassicae and the piercing-sucking aphid Brevicoryne brassicae were assessed. Brassica nigra plants grown on soil amended with BSF exuviae showed increased growth, had more flowers and flower visitors, and higher seed production. Herbivory neither affected number of flowers nor seed production, suggesting tolerance and compensatory growth responses to herbivory compared to plants growing in soil without the addition of BSF exuviae. After five weeks fewer aphids were found on plants growing in amended soil. Our findings show that BSF exuviae added to soil can positively affect tolerance to herbivory and seed production of B. nigra, an insect-pollinated plant species. Moreover, adding insect exuviae as soil amendment in the field benefits plant-pollinator mutualism and seed yield even during herbivore attack in the field. Use of by-products from insect production as soil amendment can contribute to sustainable agricultural practices along with the conservation of ecosystem services.

Plant quantity affects development and reproduction of a gregarious butterfly more than plant quality

AbstractThe larvae of insect herbivores feed on plants that may vary nutritionally (qualitatively and/or quantitatively) over the course of insect development. Plant quality may change in response to interactions with the biotic environment that in turn may affect development and biomass of the insects feeding on these plants. However, the larvae of many gregariously feeding herbivores feed on comparatively small plants with limited biomass and may also experience variation in the quantity of plant food available. Pieris brassicae L. (Lepidoptera: Pieridae) is a gregarious butterfly species laying clutches of 10–150 eggs that are often laid on small brassicaceous food plants, including the plant used in this study, Brassica nigra L. (Brassicaceae). A single B. nigra plant provides insufficient resources for the development of an entire brood of P. brassicae. In this study, we investigated the effect of both plant quality and quantity on the performance of P. brassicae when feeding on B. nigra plants. When we compared the effects of changes in plant quality induced by (1) aphid infestation, (2) exposure to pathogenic and non‐pathogenic bacteria, and (3) inbreeding depression, which are all biotic stresses known to change plant quality, pupal mass and larval development time of P. brassicae were fairly similar. We then examined the effects of quantitative food constraints during immature development on pupal mass, which correlated strongly with adult size, longevity, and fecundity. Female pupal mass, longevity and fecundity were negatively correlated with the duration of starvation during larval development. No significant effect of male starvation was found on female reproduction and longevity. Thus, P. brassicae larvae were more affected by quantitative than by qualitative constraints in terms of pupal mass, which strongly correlated with female reproduction.

Flowers prepare thyselves: leaf and root herbivores induce specific changes in floral phytochemistry with consequences for plant interactions with florivores.

Summary The phenotypic plasticity of flowering plants in response to herbivore damage to vegetative tissues can affect plant interactions with flower‐feeding organisms. Such induced systemic responses are probably regulated by defence‐related phytohormones that signal flowers to alter secondary chemistry that affects resistance to florivores. Current knowledge on the effects of damage to vegetative tissues on plant interactions with florivores and the underlying mechanisms is limited.We compared the preference and performance of two florivores on flowering Brassica nigra plants damaged by one of three herbivores feeding from roots or leaves. To investigate the underlying mechanisms, we quantified expression patterns of marker genes for defence‐related phytohormonal pathways, and concentrations of phytohormones and glucosinolates in buds and flowers.Florivores displayed contrasting preferences for plants damaged by herbivores feeding on roots and leaves. Chewing florivores performed better on plants damaged by folivores, but worse on plants damaged by the root herbivore. Chewing root and foliar herbivory led to specific induced changes in the phytohormone profile of buds and flowers. This resulted in increased glucosinolate concentrations for leaf‐damaged plants, and decreased glucosinolate concentrations for root‐damaged plants.The outcome of herbivore–herbivore interactions spanning from vegetative tissues to floral tissues is unique for the inducing root/leaf herbivore and receiving florivore combination.

Effects of Melatonin on Morus nigra cv. 'Ekşi Kara' Exposed to Drought Stress

Today, drought stress threatens the world seriously. Determining the effects of some exogenous stimulators in acquiring resistance against stress will contribute to agriculture under drought stress. In this regard, we investigated the effects of melatonin (MEL) on Morus nigra cv. 'Eksi Kara' (black mulberry) in challenging drought. To reach this object, we reproduced 'Eksi Kara', which is registered in Turkey and has economic importance, in tissue culture by using the meristem culture method. Plants were then transferred in a medium containing polyethylene glycol (PEG) 8000, which causes -1.5 MPa drought stress, and 20 μl MEL has applied. Leaf samples were taken on the 5th, 10th, and 15th days after treatments in groups of plants grown in a different medium (Control, Control+MEL, PEG and PEG+MEL). The changes in the pigment system, relative water content (RWC) and antioxidant system were evaluated comparatively between the groups to assess plants' growth and determine their roles in coping with stress. Our findings showed that RWC decreased in leaves under drought. Exogenous MEL added in MS medium had a mitigation effect on stress. The reduction was detected in the chlorophyll and carotenoid content of leaves. Moreover, MEL+PEG combination improved the chlorophyll level. It was seen that exogenous MEL application promoted the plant defence mechanism of M. nigra plants, which exposed to drought stress, by increasing the accumulation of non-enzymatic antioxidants; total glutathione (GSH), total phenolic, proline) and activities of antioxidant enzymes; catalase (CAT), superoxide dismutase (SOD), Glutathione-S-transferase (GST), glutathione reductase (GR), peroxidase (POD), ascorbate peroxidase (APX). This study also indicates that the application of MEL+PEG composition partially prevented membrane lipid peroxidation by decreasing (malondialdehyde) MDA content.

Plasticity in induced resistance to sequential attack by multiple herbivores in Brassica nigra

In nature, plants interact with multiple insect herbivores that may arrive simultaneously or sequentially. There is extensive knowledge on how plants defend themselves against single or dual attack. However, we lack information on how plants defend against the attack of multiple herbivores that arrive sequentially. In this study, we investigated whether Brassica nigra L. plants are able to defend themselves against caterpillars of the late-arriving herbivore Plutella xylostella L., when plants had been previously exposed to sequential attack by four other herbivores (P. xylostella, Athalia rosae, Myzus persicae and Brevicoryne brassicae). We manipulated the order of arrival and the history of attack by four herbivores to investigate which patterns in sequential herbivory determine resistance against the fifth attacker. We recorded that history of sequential herbivore attack differentially affected the capability of B. nigra plants to defend themselves against caterpillars of P. xylostella. Caterpillars gained less weight on plants attacked by a sequence of four episodes of attack by P. xylostella compared to performance on plants that were not previously damaged by herbivores. The number of times the plant was attacked by herbivores of the same feeding guild, the identity of the first attacker, the identity and the guild of the last attacker as well as the order of attackers within the sequence of multiple herbivores influenced the growth of the subsequent herbivory. In conclusion, this study shows that history of sequential attack is an important factor determining plant resistance to herbivores.

Alternaria Black Spot (Alternaria brassicae) Infection Severity on Cruciferous Oilseed Crops

The increase in the cultivation area of cruciferous oilseed crops and the use of short crop rotation has resulted in the enhanced spread of several major pests in Northern latitudes. There is currently limited information about incidence and severity of Alternaria black spot disease (Alternaria brassicae) on the main oilseed crop, spring oilseed rape (Brassica napus), in the Northern Baltics. Thus, spring oilseed rape and five alternative cruciferous oilseed crops were selected and their resistance to black spot disease was evaluated in field conditions during two growing seasons. We hypothesized that spring oilseed rape is more susceptible to Alternaria black spot disease than other alternative cruciferous oilseed crops. Both growing seasons were warmer and drier compared to the long-term average, and were thus suitable for A. brassicae development and assessments. In both years, incidence of Alternaria black spot infection was recorded on all cruciferous species, yet the disease development differed considerably among the crops. During both growing seasons, black mustard (B. nigra) plants were the most infected. Based on our observations during warm growing seasons we conclude that alternative oilseed crops such as Sinapis alba, Eruca sativa and Raphanus sativus are more resistant to the Alternaria black spot infection than the traditional oilseed crops and thus, possess a great potential to grow with limited chemical disease control in Northern Baltic conditions.

Chemotaxonomic Study of Four Subspecies of Pinus nigra Arn. Grown in Common Garden Based on Essential Oil Composition

The aim of this study was to investigate the chemical diversity of Pinus nigra Arn. essential oils. The research was carried out on the needles collected from eighteen provenances of black pine grown in common garden located in West-Northern Tunisia and belonging to four different subspecies (Pinus nigra subsp. nigra, Pinus nigra subsp. salzmannii, Pinus nigra subsp. pallasiana, and Pinus nigra subsp. laricio). Essential oil yields ranged from 0.19% to 0.68%. The obtained essential oils have been analyzed by GC-FID and GC-MS apparatus. Twenty-three constituents accounting about 98% of total essential oil composition were identified. The essential oil compositions appeared to be very different according to their origin. Thus, five main essential oil chemotypes were identified in Pinus nigra plants: caryophyllene oxide, camphene, ß-caryophyllene, α-amorphene, and germacrene D. The chemotaxonomic value of the essential oil compositions was discussed in relation to the results of the multivariate statistical test, including a detailed survey of the available literature data.

Combined Acute Ozone and Water Stress Alters the Quantitative Relationships between O3 Uptake, Photosynthetic Characteristics and Volatile Emissions in Brassica nigra.

Ozone (O3) entry into plant leaves depends on atmospheric O3 concentration, exposure time and openness of stomata. O3 negatively impacts photosynthesis rate (A) and might induce the release of reactive volatile organic compounds (VOCs) that can quench O3, and thereby partly ameliorate O3 stress. Water stress reduces stomatal conductance (gs) and O3 uptake and can affect VOC release and O3 quenching by VOC, but the interactive effects of O3 exposure and water stress, as possibly mediated by VOC, are poorly understood. Well-watered (WW) and water-stressed (WS) Brassica nigra plants were exposed to 250 and 550 ppb O3 for 1 h, and O3 uptake rates, photosynthetic characteristics and VOC emissions were measured through 22 h recovery. The highest O3 uptake was observed in WW plants exposed to 550 ppb O3 with the greatest reduction and poorest recovery of gs and A, and elicitation of lipoxygenase (LOX) pathway volatiles 10 min–1.5 h after exposure indicating cellular damage. Ozone uptake was similar in 250 ppb WW and 550 ppb WS plants and, in both treatments, O3-dependent reduction in photosynthetic characteristics was moderate and fully reversible, and VOC emissions were little affected. Water stress alone did not affect the total amount and composition of VOC emissions. The results indicate that drought ameliorated O3 stress by reducing O3 uptake through stomatal closure and the two stresses operated in an antagonistic manner in B. nigra.

Powdery mildew (Erysiphe cruciferarum) evaluation on oilseed rape and alternative cruciferous oilseed crops in the northern Baltic region in unusually warm growing seasons

ABSTRACT The pathogen Erysiphe cruciferarum is an increasingly serious threat to cruciferous oilseed crops worldwide. In the present study, the severity of powdery mildew was evaluated on spring oilseed rape (Brassica napus) and five alternative oilseed crop species (B. juncea, B. nigra, Sinapis alba, Raphanus sativus, Eruca sativa). The main aim of the study was to identify plant species that are less susceptible to powdery mildew for possible application as cover crop, in trap cropping or seed production. Powdery mildew assessments were conducted in two growing seasons that were characterised by unusually warm and dry conditions for northern temperate climatic conditions. In both growing seasons, a heavy powdery mildew infection (over 80%) was recorded on B. napus and B. nigra plants, indicating that E. cruciferarum is an important pathogen for oilseed crops in northern Baltics. However, three other cruciferous species S. alba, E. sativa and R. sativus showed full resistance to powdery mildew, and thus, even under strong powdery mildew pressure, they can be cultivated without pesticide application in northern Baltic conditions. We suggest that in changing climatic conditions powdery mildew is expected to become a more serious problem in cruciferous oilseed crops in northern Europe, especially under intensive short-rotation farming practices.

Insect species richness affects plant responses to multi-herbivore attack.

Summary Plants are often attacked by multiple insect herbivores. How plants deal with an increasing richness of attackers from a single or multiple feeding guilds is poorly understood.We subjected black mustard (Brassica nigra) plants to 51 treatments representing attack by an increasing species richness (one, two or four species) of either phloem feeders, leaf chewers, or a mix of both feeding guilds when keeping total density of attackers constant and studied how this affects plant resistance to subsequent attack by caterpillars of the diamondback moth (Plutella xylostella).Increased richness in phloem‐feeding attackers compromised resistance to P. xylostella. By contrast, leaf chewers induced a stronger resistance to subsequent attack by caterpillars of P. xylostella while species richness did not play a significant role for chewing herbivore induced responses. Attack by a mix of herbivores from different feeding guilds resulted in plant resistance similar to resistance levels of plants that were not previously exposed to herbivory.We conclude that B. nigra plants channel their defence responses stronger towards a feeding‐guild specific response when under multi‐species attack by herbivores of the same feeding guild, but integrate responses when simultaneously confronted with a mix of herbivores from different feeding guilds.

Multiple Attack to Inflorescences of an Annual Plant Does Not Interfere with the Attraction of Parasitoids and Pollinators

Plants in the flowering stage need to ensure reproduction by protecting themselves from attack and by preserving interactions with mutualist pollinators. When different plant mutualists are using the same type of cues, such as volatile compounds, attraction of parasitoids and pollinators may trade off. To explore this, we compared volatile emission of Brassica nigra plants in response to single or dual attack on their inflorescences. Additionally, we recorded flower visitation by pollinators and the attraction of parasitoids in the greenhouse and/or field. Brassica nigra were exposed in the flowering stage to one or two of the following three attackers: Brevicoryne brassicae aphids, Pieris brassicae caterpillars, and Xanthomonas campestris pv. raphani bacteria. We found that single attack by caterpillars, and dual attack by caterpillars plus aphids, induced the strongest changes in plant volatile emission. The caterpillars’ parasitoid C. glomerata did not exhibit preference for plants exposed to caterpillars only vs. plants exposed to caterpillars plus aphids or plus bacteria. However, the composition of the pollinator community associated with flowers of B. nigra was affected by plant exposure to the attackers, but the total number of pollinators visiting the plants did not change upon attack. We conclude that, when B. nigra were exposed to single or dual attack on their inflorescences, the plants maintained interactions with natural enemies of the insect attackers and with pollinators. We discuss how chemical diversity may contribute to plant resilience upon attack.

First Report of Powdery Mildew Caused by Erysiphe viciae-unijugae on Vicia sativa subsp. nigra in Korea.

Vicia sativa subsp. nigra, also known as narrow-leaved vetch, belongs to the family Fabaceae and is distributed in different countries.Vetch is one of the most important annual forage legumes in the world; it is used as hay, grain, silage, green manure, and livestock fodder. In Korea, this plant is often used as cattle feed. In early May of 2019 and 2020, a powdery mildew was observed on leaves of V. sativa subsp. nigra plants in a garden of Chonnam National University, Gwangju, Korea. The first symptom appeared on the upper surface of the leaves as a small white spot. Within two weeks, the white spots of powdery mildew spread and covered the entire leaf. Voucher specimens were deposited at the Environmental Microbiology Laboratory Herbarium, Chonnam National University, Gwangju, Korea, under the accession numbers CNUFC PWV1 and CNUFC PWV2. The hyphal appressoria of the fungus were nipple-shaped, moderately lobed or multilobed, single or in opposite pairs. Measurements were made of 35 conidiophores and 55 conidia. Conidiophores arising from the upper part of mother cells, were cylindrical, 60.5 to 117.5 × 7.5 to 9.5 μm. The foot cells of the conidiophores were cylindrical, straight to slightly curved at the base, 23.5 to 38.7 × 7.3 to 9.2 μm, followed by 2-3 shorter cells. Conidia were formed singly, subcylindrical to oval, 32.5 to 48.7 × 13.5 to 19.7 μm. Conidia produced short to long germ tubes, terminating in lobed or unlobed appressoria. No chasmothecia were observed. The morphological characteristics of conidiophores and conidia were consistent with the description of Erysiphe viciae-unijugae in Shin (2000). However, it was not possible to identify the fungus only based on the asexual morph. In addition, the conidiophore and conidium shapes of E. baeumleri on the known host V. sativa were similar to those of E. viciae-unijugae (Braun and Cook 2012). Therefore, genomic DNA was extracted directly from the mycelia and conidia using a DNA prep kit (Solgent, Daejeon, Korea). The internal transcribed spacer (ITS) regions ofribosomal DNA (rDNA) and 28S rDNA from the two specimens were amplified using the primers ITS5 and PM6 (Takamatsu and Kano 2001), and LROR and LR3 (Vilgalys and Hester 1990), respectively. A BLASTn search with the ITS sequences indicated that CNUFC PWV1 (GenBank accession no. MT509395) and CNUFC PWV2 (MT509396) were 100% (503/503 bp) and 99.8% (502/503 bp) identical to those of E. viciae-unijugae (LC010086 and LC009962), respectively. The 28S sequences of CNUFC PWV1 (MT705629) and CNUFC PWV2 (MT705630) showed 99.8% (507/508 bp) and 99.4% (505/508 bp) identity values with E. viciae-unijugae (LC009976 and LC010029), respectively. Phylogenetic analyses based on the combined ITS and 28S rDNA sequences indicated that the two specimens, CNUFC PWV1 and CNUFC PWV2, formed a monophyletic clade together with sequences retrieved from E. viciae-unijugae. Therefore, the causal pathogen was identified as E. viciae-unijugae based on the results of morphological and molecular analyses. Pathogenicity tests were performed by gently pressing the infected leaves onto 10 young leaves of three healthy plants. A non-inoculated plant was used as a control. The plants were maintained in a greenhouse at 22 to 25°C, with relative humidity around 75%, and natural light. Powdery mildew symptoms were observed on the inoculated leaves after 10-14 days, whereas no symptoms were observed on the leaves of the control. The fungi on the inoculated leaves were morphologically identical to the fungi on the original infected leaves. Erysiphe viciae-unijugae has been reported to occur on Lathyrus spp. and Vicia spp. (Farr and Rossman 2020). To our knowledge, this is the first report of powdery mildew caused by E. viciae-unijugae on V. sativa subsp. nigra in Korea. The weather conditions, especially during May, are favorable for disease outbreaks. This disease may be a potential threat to feed production in Korea.

Allelopathic effects of native and invasive Brassica nigra do not support the novel-weapons hypothesis.

The novel-weapons hypothesis predicts that some plants are successful invaders because they release allelopathic compounds that are highly suppressive to naïve competitors in invaded ranges but are relatively ineffective against competitors in the native range. For its part, the evolution of enhanced weaponry hypothesis predicts that invasive populations may evolve increased expression of the allelopathic compounds. However, these predictions have rarely been tested empirically. Here, we made aqueous extracts of roots and shoots of invasive (North American) and native (European) Brassica nigra plants. Seeds of nine species from North America and nine species from Europe were exposed to these extracts. As control solutions, we used pure distilled water and distilled water with the osmotic potential adjusted with polyethylene glycol (PEG) to match that of root and shoot extracts of B.nigra. The extracts had a strong negative effect on germination rates and seedling root lengths of target species compared to the water-control. Compared to the osmolality-adjusted controls, the extracts had a negative effect on seedling root length. We found no differences between the effects of B.nigra plant extracts from the invasive vs. native populations on germination rates and seedling root growth of target plant species. Responses were largely independent of whether the target plant species were from the invaded or native range of B.nigra. The results show that B.nigra can interfere with other species through allelochemical interactions, but do not support predictions of the novel-weapons hypothesis and evolution of increased allelopathy.

Spatial scale, neighbouring plants and variation in plant volatiles interactively determine the strength of host–parasitoid relationships

Species‐specific responses to the environment can moderate the strength of interactions between plants, herbivores and parasitoids. However, the ways in which characteristics of plants, such as genotypic variation in herbivore induced volatiles (HIPVs) that attract parasitoids, affect trophic interactions in different contexts of plant patch size and plant neighbourhood is not well understood. We conducted a factorial field experiment with white cabbage Brassica oleracea accessions that differ in the attractiveness of their HIPVs for parasitoids, in the context of different patch sizes and presence or absence of surrounding Brassica nigra plants. Parasitism rates of experimentally introduced Pieris brassicae caterpillars and the presence of naturally occurring Pieris spp. caterpillars in the plots were assessed throughout the growing season. The abundance of Pieris caterpillars was neither affected by cabbage accession nor plot size. Later in the season, when B. nigra plants had senesced, fewer caterpillars were found on cabbage plants in plots with a B. nigra border. Parasitism rates fluctuated over the season, and were not affected by plot size. However, the B. nigra border negatively affected parasitism rates on the accession that is less attractive to the parasitoid Cotesia glomerata, but not on the more attractive accession. Our results show that plant variation in HIPVs can differentially influence herbivores and parasitoids depending on characteristics of the surrounding vegetation context. These findings underscore the importance of considering the interaction between focal plant traits and neighbourhood context to reliably predict trophic cascades.

The phytotoxic air-pollutant O3 enhances the emission of herbivore-induced volatile organic compounds (VOCs) and affects the susceptibility of black mustard plants to pest attack

Stress-induced changes to plant biochemistry and physiology can influence plant nutritional quality and subsequent interactions with herbivorous pests. However, the effects of stress combinations are unpredictable and differ to the effects of individual stressors. Here we studied the effects of exposure to the phytotoxic air-pollutant ozone (O3), feeding by larvae of the large cabbage white butterfly (Pieris brassicae), and a combination of the two stresses, on the emission of volatile organic compounds (VOCs) by black mustard plants (Brassica nigra) under field and laboratory conditions. Field-grown B. nigra plants were also measured for carbon-nitrogen (C–N) content, net photosynthetic activity (Pn), stomatal conductance (gs) and biomass. The effects of O3 on interactions between plants and a herbivorous pest were addressed by monitoring the abundance of wild diamondback moth larvae (Plutella xylostella) and feeding-damage to B. nigra plants in an O3-free air concentration enrichment (O3-FACE) field site. Herbivore-feeding induced the emission of VOCs that were not emitted by undamaged plants, both under field and laboratory conditions. The combination of O3 and herbivore-feeding stresses resulted in enhanced emission rates of several VOCs from field-grown plants. Short-term O3 exposure (of 10 days) and P. brassicae-feeding did not affect C–N content, but chronic O3 exposure (of 34 and 47 days) and P. brassicae-feeding exacerbated suppression of Pn. Ozone exposure also caused visible injury and decreased the plant biomass. Field-grown B. nigra under elevated O3 were infested with fewer P. xylostella larvae and received significantly less feeding damage. Our results suggest that plants growing in a moderately polluted environment may be of reduced quality and less attractive to foraging herbivores.