Nigra Plants Research Articles

First report of southern root-knot nematode, Meloidogyne incognita, infecting Brassica nigra in Peru.

Brassica nigra plants showing symptoms caused by root-knot nematodes were detected in the municipality of La Joya, Arequipa Province, Peru. Based on morphology, esterase phenotypes, and species-specific characterized amplified region (SCAR) sequence, the causal agent was identified as Meloidogyne incognita. Pathogenicity was confirmed by a modified version of Koch’s postulates. To our knowledge, this is the first report of M. incognita infecting Brassica nigra in Peru.

Settling on leaves or flowers: herbivore feeding site determines the outcome of indirect interactions between herbivores and pollinators

Herbivore attack can alter plant interactions with pollinators, ranging from reduced to enhanced pollinator visitation. The direction and strength of effects of herbivory on pollinator visitation could be contingent on the type of plant tissue or organ attacked by herbivores, but this has seldom been tested experimentally. We investigated the effect of variation in feeding site of herbivorous insects on the visitation by insect pollinators on flowering Brassica nigra plants. We placed herbivores on either leaves or flowers, and recorded the responses of two pollinator species when visiting flowers. Our results show that variation in herbivore feeding site has profound impact on the outcome of herbivore–pollinator interactions. Herbivores feeding on flowers had consistent positive effects on pollinator visitation, whereas herbivores feeding on leaves did not. Herbivores themselves preferred to feed on flowers, and mostly performed best on flowers. We conclude that herbivore feeding site choice can profoundly affect herbivore–pollinator interactions and feeding site thereby makes for an important herbivore trait that can determine the linkage between antagonistic and mutualistic networks.

Підсумки інвентаризації Pinus Nigra Arn. у складі вуличних насаджень міста Умань

Досліджено таксономічний склад та проведено географічний аналіз P. nigra у вуличних насадженнях Умані. На підставі відповідності віковим параметрам діаметра та висоти її окремих екземплярів, відзначено високу стійкість рослин до складних умов урбанізованого середовища та встановлено перспективність використання виду, за дії на нього чисельних антропогенних факторів. Результати показують, що всі досліджувані рослини P. nigra мають високі показники життєздатності та належать до першої групи перспективності. Значення акліматизаційних чисел свідчать про перспективність інтродукції P. nigra та успішність акліматизації в умовах урбанізованого середовища. Оцінивши декоративні якості P. nigra, виявлено, що в основному вона виділяється на фоні інших видів своєю компактною овальною чи конусоподібною кроною, темно-сірою з різними відтінками тріщинуватою корою та довгою темно-зеленою хвоєю. Саме завдяки цим якостям вона зберігає привабливий вигляд протягом усього року, навіть у зимовий період. На підставі отриманих результатів, сумарний річний показник декоративності основних ознак P. nigra становить 4 бали і свідчить про наявність високих декоративних якостей рослин цього виду. Отже, використання P. nigra в урбанізованому середовищі покращує екологічні умови міста та позитивно впливає на емоційний стан населення.

Physiological and antioxidative response of Brassica nigra (L.) to ZnO nanoparticles grown in culture media and soil

To investigate metal nanoparticle-induced phytotoxicity, Brassica nigra seeds were exposed to 50–1000 mg L−1 ZnO nanoparticles in culture media and 100–1000 mg kg−1 in soil. Plant length and weight were adversely affected in culture conditions, but with soil the effect was not significant. Determination of the radical-scavenging potential revealed that soil grown plants were less stressed than plants grown on culture medium. The total antioxidant and reducing power potential of soil grown plants were less variable compared to plants grown on culture medium. Total phenolic and flavonoid concentrations varied in plants, which changed with the nanoparticle’s concentrations in medium and soil. High performance liquid chromatography analysis showed that rutin was the major antioxidative molecule that significantly increased in nanoparticles-stressed B. nigra plants.

Floral plasticity: Herbivore-species-specific-induced changes in flower traits with contrasting effects on pollinator visitation.

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant–pollinator interactions. Current knowledge on the full extent of herbivore‐induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore‐induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species‐specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant‐mediated interactions with mutualists.

Dynamic changes in ABA content in water-stressed Populus nigra: effects on carbon fixation and soluble carbohydrates.

Hydraulic and chemical signals operate in tandem to regulate systemic plant responses to drought. Transport of abscisic acid (ABA) through the xylem and phloem from the root to shoot has been suggested to serve as the main signal of water deficit. There is evidence that ABA and its ABA-glycosyl-ester (ABA-GE) are also formed in leaves and stems through the chloroplastic 2-C-methylerythritol-5-phosphate (MEP) pathway. This study aimed to evaluate how hormonal and hydraulic signals contribute to optimize stomatal (gs), mesophyll (gm) and leaf hydraulic (Kleaf) conductance under well-watered and water-stressed conditions in Populus nigra (black poplar) plants. In addition, we assessed possible relationships between ABA and soluble carbohydrates within the leaf and stem. Plants were subjected to three water treatments: well-watered (WW), moderate stress (WS1) and severe stress (WS2). This experimental set-up enabled a time-course analysis of the response to water deficit at the physiological [leaf gas exchange, plant water relations, (Kleaf)], biochemical (ABA and its metabolite/catabolite quantification in xylem sap, leaves, wood, bark and roots) and molecular (gene expression of ABA biosynthesis) levels. Our results showed strong coordination between gs, gm and Kleaf under water stress, which reduced transpiration and increased intrinsic water use efficiency (WUEint). Analysis of gene expression of 9-cis-epoxycarotenoid dioxygenase (NCED) and ABA content in different tissues showed a general up-regulation of the biosynthesis of this hormone and its finely-tuned catabolism in response to water stress. Significant linear relationships were found between soluble carbohydrates and ABA contents in both leaves and stems, suggesting a putative function for this hormone in carbohydrate mobilization under severe water stress. This study demonstrates the tight regulation of the photosynthetic machinery by levels of ABA in different plants organs on a daily basis in both well-watered and water stress conditions to optimize WUEint and coordinate whole plant acclimation responses to drought.

Responses of insect herbivores and their food plants to wind exposure and the importance of predation risk.

Wind is an important abiotic factor that influences an array of biological processes, but it is rarely considered in studies on plant-herbivore interactions. Here, we tested whether wind exposure could directly or indirectly affect the performance of two insect herbivores, Plutella xylostella and Pieris brassicae, feeding on Brassica nigra plants. In a greenhouse study using a factorial design, B.nigra plants were exposed to different wind regimes generated by fans before and after caterpillars were introduced on plants in an attempt to separate the effects of direct and indirect wind exposure on herbivores. Wind exposure delayed flowering, decreased plant height and increased leaf concentrations of amino acids and glucosinolates. Plant-mediated effects of wind on herbivores, that is effects of exposure of plants to wind prior to herbivore feeding, were generally small. However, development time of both herbivores was extended and adult body mass of P.xylostella was reduced when they were directly exposed to wind. By contrast, wind-exposed adult P.brassicae butterflies were significantly larger, revealing a trade-off between development time and adult size. Based on these results, we conducted a behavioural experiment to study preference by an avian predator, the great tit (Parus major) for last instar P.brassicae caterpillars on plants that were exposed to either control (no wind) or wind (fan-exposed) treatments. Tits captured significantly more caterpillars on still than on wind-exposed plants. Our results suggest that P.brassicae caterpillars are able to perceive the abiotic environment and to trade off the costs of extended development time against the benefits of increased size depending on the perceived risk of predation mediated by wind exposure. Such adaptive phenotypic plasticity in insects has not yet been described in response to wind exposure.

Dealing with mutualists and antagonists: Specificity of plant‐mediated interactions between herbivores and flower visitors, and consequences for plant fitness

Abstract Plants need to deal with antagonists, such as herbivores, while maintaining interactions with mutualists, such as pollinators that help plants to maximize their reproductive output. Although many plant species have inducible defences to save metabolic costs of defence in the absence of herbivores, plant responses induced by herbivore attack can have ecological costs. For example, herbivore‐induced responses can affect flower traits and alter interactions with flower visitors. Such plant‐mediated interactions between herbivores and flower visitors can affect plant reproductive output. Current knowledge on the generality and specificity of plant‐mediated herbivore–flower–visitor interactions and its consequences for plant fitness is limited. In this study, we investigated whether a broad range of herbivores feeding on the annual plant Brassica nigra affect interactions with flower visitors, whether the direction of interactions is predicted by the feeding modes (chewing and sap‐feeding) and sites (above‐ and belowground) of the herbivores, and whether it results in fitness consequences for the plant. Our results show that attack of B. nigra by a range of different herbivores influenced plant interactions with mutualist pollinators and an antagonist florivore, the pollen beetle Meligethes aeneus. Pollinator community composition was affected by herbivory, whereas overall pollinator attraction was maintained. Pollinator community composition of uninfested plants differed from that of chewing and root herbivore‐infested plants. Main responders in the pollinator communities to changes induced by herbivory were syrphid flies, bumblebees, and solitary bees. Although the preference of pollen beetle adults was not affected by herbivory, beetle larvae performed best on plants infested with the nematode Heterodera schachtii. The changes in pollinator community composition and syrphid fly visitation can explain the observed increase in seed set of root herbivore‐infested plants. Interactions of flowering B. nigra plants with mutualist and antagonist insects are well integrated and conflicting interactions do not reduce reproductive output. Our results suggest some degree of specificity in herbivore–flower–visitor interactions with consequences for plant fitness. Specificity of plant responses were determined at the species level as well as the herbivore functional group level, and differed depending on the flower visitor. Because plant reproduction was affected by indirect plant‐mediated interactions, these can potentially result in selection on plant strategies to optimize growth, defence and reproduction. A plain language summary is available for this article.

When does it pay off to prime for defense? A modeling analysis.

Summary Plants can prepare for future herbivore attack through a process called priming. Primed plants respond more strongly and/or faster to insect attack succeeding the priming event than nonprimed plants, while the energetic costs of priming are relatively low.To better understand the evolution of priming, we developed a simulation model, partly parameterized for Brassica nigra plants, to explore how the fitness benefits of priming change when plants are grown in different biotic environments.Model simulations showed that herbivore dynamics (arrival probability, arrival time, and feeding rate) affect the optimal duration, the optimal investment and the fitness benefits of priming. Competition for light increases the indirect costs of priming, but may also result in a larger payoff when the nonprimed plant experiences substantial leaf losses.This modeling approach identified some important knowledge gaps: herbivore arrival rates on individual plants are rarely reported but they shape the optimal duration of priming, and it would pay off if the likelihood, severity and timing of the attack could be discerned from the priming cue, but it is unknown if plants can do so. In addition, the model generated some testable predictions, for example that the sensitivity to the priming cue decreases with plant age.

In the presence of specialist root and shoot herbivory, invasive‐range Brassica nigra populations have stronger competitive effects than native‐range populations

SUMMARY The evolution of increased competitive ability (EICA) hypothesis predicts that release from specialist herbivores enables invasive plants to evolve increased growth. The most powerful tests of EICA hypothesis are provided by approaches that simultaneously assess the effects of specialist herbivory and competitive interactions. However, such approaches are extremely rare, and hence how simultaneous release from root and shoot herbivory influence competitive ability of invasive plants remains little understood. Here, we tested whether invasive‐range Brassica nigra plants have evolved increased competitive ability, and whether expression of competitive ability depends on separate and simultaneous effects of specialist root and shoot herbivory. To do this, we grew B. nigra plants from eight invasive‐range and eight native‐range populations in the presence vs. absence of competition with a community of native plant species, and in the absence vs. presence of separate and simultaneous damage by a specialist root herbivore (Delia radicum) and a specialist shoot herbivore (Plutella xylostella). Brassica nigra performance was assessed by measuring biomass production and flowering of individual B. nigra plants. In partial support of the EICA hypothesis, invasive‐range B. nigra had greater flowering than native‐range conspecifics in the absence of competition. However, contrary to a prediction of the EICA hypothesis, invasive‐range B. nigra produced less above‐ground biomass than native‐range B. nigra in the absence of shoot herbivory and competition. Moreover, with simultaneous root and shoot herbivory, invasive‐range B. nigra suppressed a competing community more strongly than native‐range B. nigra did. Synthesis. Our results suggest that invasiveness may be driven by mechanisms other than increased individual size. Simultaneous root and shoot herbivory in the invasive range may enhance suppressive effects of introduced plant species that have not completely escaped herbivore damage in the introduced range.

Dual herbivore attack and herbivore density affect metabolic profiles of Brassica nigra leaves.

Plant responses to dual herbivore attack are increasingly studied, but effects on the metabolome have largely been restricted to volatile metabolites and defence-related non-volatile metabolites. However, plants subjected to stress, such as herbivory, undergo major changes in both primary and secondary metabolism. Using a naturally occurring system, we investigated metabolome-wide effects of single or dual herbivory on Brassica nigra plants by Brevicoryne brassicae aphids and Pieris brassicae caterpillars, while also considering the effect of aphid density. Metabolomic analysis of leaf material showed that single and dual herbivory had strong effects on the plant metabolome, with caterpillar feeding having the strongest influence. Additionally, aphid-density-dependent effects were found in both the single and dual infestation scenarios. Multivariate analysis revealed treatment-specific metabolomic profiles, and effects were largely driven by alterations in the glucosinolate and sugar pools. Our work shows that analysing the plant metabolome as a single entity rather than as individual metabolites provides new insights into the subcellular processes underlying plant defence against multiple herbivore attackers. These processes appear to be importantly influenced by insect density.

Endure and call for help: strategies of black mustard plants to deal with a specialized caterpillar

SummaryPlants have evolved inducible resistance and tolerance mechanisms against insect herbivores. Resistance mechanisms that affect herbivorous insects directly can be effective against generalist herbivores, but will not deter specialist herbivores from attacking the plant. Tolerance mechanisms and indirect plant resistance are more likely effective strategies used by plants when dealing with specialist herbivores. However, inducible indirect resistance and tolerance mechanisms have rarely been investigated within the same study system.We studied multiple tolerance mechanisms and the role of natural enemies in reducing fitness loss ofBrassica nigraplants incurred by feeding by the specialist herbivorePieris brassicae. For this, we measured the changes in carbon and nitrogen triggered by herbivore attack and quantified plant biomass and seed production under field conditions, in the presence or absence of natural enemies of the herbivores. We also assessed whetherB. nigraincreased selfing rates when exposed to herbivore infestation, and investigated whether infestation byP. brassicaerenderedB. nigraplants more attractive to night‐active pollinators than control plants.We found thatB. nigraflowers are rarely visited by insects during the night, and exposure to herbivores did not influence selfing rates.Brassica nigraplants compensated for herbivory in terms of vegetative biomass. Seed set was negatively affected by herbivory in the absence of natural enemies, but not in the presence of natural enemies. Plants responded to herbivory with drastic changes in nitrogen contents of leaves and flowers, whereas no changes in carbon concentrations were detected.The investment in reproduction or re‐growth of vegetative tissues is not sufficient to sustain plant fitness. Reproductive output of flowering mustard plants is only sustained when interactions with the natural enemies of the herbivores are preserved. We conclude that natural enemies of herbivorous insects play an important role as component of the plant's defence strategy. This study reveals that both tolerance and indirect resistance are strategies of this plant species to sustain fitness.

How specialized volatiles respond to chronic and short-term physiological and shock heat stress in Brassica nigra.

Brassicales release volatile glucosinolate breakdown products upon tissue mechanical damage, but it is unclear how the release of glucosinolate volatiles responds to abiotic stresses such as heat stress. We used three different heat treatments, simulating different dynamic temperature conditions in the field to gain insight into stress-dependent changes in volatile blends and photosynthetic characteristics in the annual herb Brassica nigra (L.) Koch. Heat stress was applied by either heating leaves through temperature response curve measurements from 20 to 40 °C (mild stress), exposing plants for 4 h to temperatures 25-44 °C (long-term stress) or shock-heating leaves to 45-50 °C. Photosynthetic reduction through temperature response curves was associated with decreased stomatal conductance, while the reduction due to long-term stress and collapse of photosynthetic activity after heat shock stress were associated with non-stomatal processes. Mild stress decreased constitutive monoterpene emissions, while long-term stress and shock stress resulted in emissions of the lipoxygenase pathway and glucosinolate volatiles. Glucosinolate volatile release was more strongly elicited by long-term stress and lipoxygenase product released by heat shock. These results demonstrate that glucosinolate volatiles constitute a major part of emission blend in heat-stressed B. nigra plants, especially upon chronic stress that leads to induction responses.

Compatible and incompatible pathogen–plant interactions differentially affect plant volatile emissions and the attraction of parasitoid wasps

Summary The effects of multiple insect attacks on herbivore‐induced plant volatiles and carnivorous arthropods are increasingly studied. Phytopathogens also represent an important threat to plants, and plant defence strategies against pathogens and insects are strongly interconnected, yet the potential impact of pathogens on insect‐induced volatiles has been largely overlooked, and degree of pathogenicity is rarely considered. We investigated how pathogen challenge, with virulent and avirulent strains of Xanthomonas campestris either alone or with simultaneous Pieris brassicae caterpillar herbivory, affected the volatile emissions of Brassica nigra plants. The impact of these volatiles on the foraging behaviour of Cotesia glomerata parasitoids wasps was then assessed. Pathogens themselves induced volatiles that were highly attractive to parasitoids, and enhanced the attractiveness of host‐infested plant volatiles. Chemical analyses revealed that virulent and avirulent strains differentially induced plant volatiles, with primarily sesquiterpene, homoterpene and green leaf volatile compounds contributing to the differences. Strong similarities were found in the blends induced by the virulent strain and caterpillar herbivory. Challenge by either virulent or avirulent pathogens has a significant impact on plant chemistry and its interactions with other community members, demonstrating the importance of integrating pathogen‐ and insect‐based research to broaden our knowledge of plant defences under conditions of increasing complexity. A lay summary is available for this article.

Vetch aphid, Megoura crassicauda (Hemiptera: Aphididae), parasitism does not reduce the bean production of narrow-leaved vetch, Vicia sativa subsp. nigra (Fabaceae)

Megoura crassicauda Mordvilko (Hemiptera: Aphididae) is a dominant aphid species found on Vicia sativa subsp. nigra (L.) Ehrh. (Fabaceae) in the spring. Worker ants of Formica japonica, the dominant ant species attracted to the extrafloral nectaries of V. s. nigra, often attack ladybirds (Coccinella septempunctata), which are aphid enemies. However, the workers of F. japonica do not attack or exclude M. crassicauda, the non-myrmecophilous aphid. It appears that the “bodyguard” retained by the plant guards the plant’s herbivore by attacking the herbivores’ enemies, rather than guarding the plant itself. The relationship between V. s. nigra and M. crassicauda was observed in the field to examine and evaluate the cost of parasitism. Parasitism by M. crassicauda delayed flower bud formation markedly in V. s. nigra but did not kill the plants. V. s. nigra plants that were parasitized showed a net bean production similar to that of the non-parasitized controls. The parasitism rate of M. crassicauda increased when extrafloral nectaries were used by F. japonica. These results may indicate that M. crassicauda provides V. s. nigra with benefits by preventing other serious disadvantages.

The Interaction between Root Herbivory and Competitive Ability of Native and Invasive-Range Populations of Brassica nigra.

The evolution of increased competitive ability (EICA) hypothesis predicts that escape from intense herbivore damage may enable invasive plants to evolve higher competitive ability in the invasive range. Below-ground root herbivory can have a strong impact on plant performance, and invasive plants often compete with multiple species simultaneously, but experimental approaches in which EICA predictions are tested with root herbivores and in a community setting are rare. Here, we used Brassica nigra plants from eight invasive- and seven native-range populations to test whether the invasive-range plants have evolved increased competitive ability when competing with Achillea millefolium and with a community (both with and without A. millefolium). Further, we tested whether competitive interactions depend on root herbivory on B. nigra by the specialist Delia radicum. Without the community, competition with A. millefolium reduced biomass of invasive- but not of native-range B. nigra. With the community, invasive-range B. nigra suffered less than native-range B. nigra. Although the overall effect of root herbivory was not significant, it reduced the negative effect of the presence of the community. The community produced significantly less biomass when competing with B. nigra, irrespective of the range of origin, and independent of the presence of A. millefolium. Taken together, these results offer no clear support for the EICA hypothesis. While native-range B. nigra plants appear to be better in dealing with a single competitor, the invasive-range plants appear to be better in dealing with a more realistic multi-species community. Possibly, this ability of tolerating multiple competitors simultaneously has contributed to the invasion success of B. nigra in North America.

Visual and odour cues: plant responses to pollination and herbivory affect the behaviour of flower visitors

SummaryPlants evolved strategies to attract pollinators that are essential for reproduction. However, plant defence against herbivores may trade off with pollinator attraction.Here, we investigated the role of inducible plant secondary metabolites in such a trade‐off. Our objective was to reveal the mechanisms underlying the effects of induced plant responses to pollination and herbivory. We assessed how responses of plants to pollination and insect herbivory affect the behaviour of flower visitors. Subsequently, we investigated how the production of volatile and non‐volatile compounds changes after pollination and herbivory.Both herbivores and pollinators induced important phenotypic changes in flowers.Brassica nigraplants respond to pollination and herbivory with changes in the profile of volatiles and non‐volatiles of their flowers. Our results show that butterflies use different cues when searching for an oviposition site or a nectar source. Pollination status influenced the behaviour of butterflies, but not that of syrphid flies.We discuss the results in the context of the trade‐off between defence and reproduction in plants and suggest that systemic responses to herbivores can interfere with local responses to pollination. Therefore, these responses must be addressed in an integrated way because, in nature, plants are simultaneously exposed to herbivores and pollinators.

LECTINS OF SAMBUCUS NIGRA AS BIOLOGICALLY ACTIVE AND DNA-PROTECTIVE SUBSTANCES

The human genome is affected by diverse environmental pollution factors and this is particularly acute for Ukrainians who have suffered from the Chernobyl radiation disaster. At the same time many natural compounds, especially from medicinal plants, are known as agents that prevent DNA lesions which often result in increasing mutagenesis and carcinogenesis. The aim of our work was to study the DNA-protective potential of biologically active compounds found in Sambucus nigra called lectins, a very large group of universally occurring proteins that recognize and specifically bind to carbohydrates/glycoconjugates. Various physiological activities of lectins based on protein-carbohydrate interactions have been demonstrated in all living forms. For example, lectins participate in host defense in plants against stress-related conditions, the attack of phytopathogens and phytophagous insects, as well as modulation of immune response, mitogenic stimulation or induction of apoptosis in animals. Antiviral, immunomodulating, antioxidant and insulin-stimulating properties of S. nigra fruit and flower extracts have been described in scientific literature. Also the elderberry lectins were found in roots, leaves, bark, seeds and fruits, the latter (SNA-IV) being the predominant protein in the juice. In Ukraine, various parts of S. nigra plants are used in folk medicine. Using methods of isoelectric focusing and chromatography, we determined that elderberry flowers and pollen contain rather high levels of lectins agglutinating animal and human erythrocytes, which differ from a commercial preparation of S. nigra bark lectin (SNA-I). The major lectin found in inflorescences, named SNAflu-I, is GalNAc/Gal specific and is supposed to be a heterotetramer with subunits of about 30 and 33 kDa. Sambucus nigra lectins demonstrated protective effects against heavy metals (nickel ions) in soil bacteria Bacillus subtilis. Also it was shown that lectins under study can modulate, in a concentration-dependent manner, the frequency of mutations and genotoxic activity of alkylating agents in eukaryotic cell cultures. Studies focused on the elucidation of cell targets sensitive to S. nigra lectins and demonstrated that at least one of the targets may be the DNA-dependent synthesis of RNA – the way to modulate gene expression. The results obtained lead to the conlusion that the protective functions of lectins both in pro- and eukaryotes involve complex mechanisms including components of the DNA repair system.

Dieback of Pinus nigra Seedlings Caused by a Strain of Trichoderma viride.

Four different fungi (Trichoderma viride, T. harzianum, Phomopsis sp., and Mortierella sp.) were isolated from 6-year-old Pinus nigra plants showing stunting and high incidence of mortality in a reforestation area of the National Park of Abruzzo, Lazio, and Molise (central Italy). Tests conducted on P. nigra revealed the pathogenic behavior of T. viride isolates with 30 to 80% mortality in artificially inoculated 2-year-old seedlings. The pathogenicity of these isolates was also observed in 10-year-old P. nigra trees and on lemon fruit. This result, in agreement with the constant isolation of T. viride from diseased plants, suggests the possible role of this fungus in the decline of P. nigra plants. T. harzianum and two reference isolates of T. viridarium and T. trixiae did not cause any symptoms, while Phomopsis sp. and Mortierella sp. caused limited necroses around the inoculation point in a few seedlings. Their role in the decline of P. nigra seedlings was considered irrelevant. According to phylogenetic analyses, pathogenic isolates of T. viride clustered in a very uniform group containing strains from different geographic origin and hosts, but none previously reported as a biocontrol agent.

Small-scale spatial resource partitioning in a hyperparasitoid community

Plant-herbivore-natural enemy associations underpin ecological communities, and such interactions may go up to four (or even more) trophic levels. Here, over the course of a growing season, we compared the diversity of secondary hyperparasitoids associated with a common host, Cotesia glomerata, a specialized larval endoparasitoid of cabbage butterfly caterpillars that in turn feed on brassicaceous plants. Cocoon clusters of C. glomerata were pinned to ~30 Brassica nigra plants by pinning them either to branches in the canopy (~1.5 m high) or to the base of the stem near the ground. The cocoons were collected a week later and reared to determine which hyperparasitoid species emerged from them. This was done in four consecutive months (June–September). Cocoons placed in the canopy were primarily attacked by specialized winged hyperparasitoids (Lysibia nana, Acrolyta nens), whereas cocoons on the ground were attacked by both winged and generalist wingless hyperparasitoids (Gelis acarorum, G. agilis), although this changed with season. There was much more temporal variation in the diversity and number of species attacking cocoons in the canopy than on the ground; the abundance of L. nana and A. nens varied from month to month, whereas P. semotus was only prevalent in August. By contrast, G. acarorum was abundant in all of the samples placed near the ground. Our results show that hyperparasitoids partition host resources at remarkably small vertical spatial scales. We argue that spatial differences in the distribution of natural enemies can contribute to the diversity patterns observed in the field.