Allelochemical Response Research Articles

Homology-based characterization of the cis-regulatory elements modulate flavone induction of CYP321A1 in Helicoverpa armigera

Xenobiotic response element (XRE) to flavone was the cis- regulatory elements that mediates the induction of the allelochemical-metabolizing CYP321A1 gene from Helicoverpa zea. However, it was unknown whether the XRE-Fla element existed in other species. Recently we have identified and cloned the CYP321A1 gene with promoter region in a related species, Helicoverpa armigera. Sequence similarity of two orthologous CYP321A1 genes was 97.27%, but the promoter sequence similarity was only 56.32%. Sequence alignment showed the XRE-Fla like element owns three mutations in H. armigera compared with H. zea. Progressive 5′ deletions and internal mutation indicated that H. armigera XRE-Fla was the essential element of CYP321A1 gene in response to flavone. XRE-Fla mutations and EMSA analysis confirmed that the H. armigera XRE-Fla element binding factor was stronger than H. zea. The findings indicate the XRE element mutations mainly contribute to the differences between the flavone-induced expressions of two CYP321A1 genes, which improve the flexibility and adaptability for allelochemical response of H. armigera.

Response of selected nutrient elements in leaf tissues of sweet potato cv. 'Bophelo' to Nemafric-BL phytonematicide

Nemafric-BL phytonematicide is a potent plant-based nematicide which consistently suppress nematode population densities of root-knot (Meloidogyne species) nematodes on various crops, but with limited information on its effects on foliar nutrient elements in sweet potato. The objective of this study, therefore, was to investigate the effects of Nemafric-BL phytonematicide on accumulation of nutrient elements in leaf tissues of sweet potato cv. 'Bophelo' under greenhouse conditions in Limpopo Province, South Africa, during autumn (February-April) in 2021 and validated in 2022. The product was applied weekly at geometric concentrations, with mature leaves collected and prepared for analysis of nutrient elements at eight weeks. Seasonal interactions were not significant and therefore data were pooled (n = 70) and then subjected to the Curve-fitting Allelochemical Response Dose (CARD) algorithm computer model. Iron (R2 = 0.86), K (0.91) and Na (0.82) versus Nemafric-BL phytonematicide each exhibited negative quadratic relations, whereas Zn (0.83) versus the product exhibited positive quadratic relations. In all test elements, the CARD-generated biological indices illustrated that the accumulation of elements was highly sensitive to the concentration of Nemafric-BL phytonematicide. In conclusion, in sweet potato production, the application of Nemafric-BL phytonematicide can inhibit (Fe, K) and stimulate (Zn) the accumulation of certain elements in leaf tissues of sweet potato cv. ′Bophelo‵.

Weed competitive ability in wheat: a peek through in its functional significance, present status and future prospects.

Weed competitive ability of a crop is one of the most widely explored aspects in the current scenario of aftermaths of synthetic herbicides such as herbicide resistant weeds emergence, residue accumulation in trophic levels; increased demands of organic produce, global climatic shifts, and other environmental issues. Further weed infestations are known to cause much more economic losses relative to crop attacks by pests. To understand the basic characteristics and underlying processes governing the competitive ability of a crop is therefore prudent, particularly in staples such as wheat. We discuss here an overview of the existing attributes of wheat-weed environment, the significance of crop competitiveness and various associated above-ground and below-ground traits (pertaining to early seed vigor and early seedling germination) discerned through biological, classical genetics and high throughput omics toolbox to provide numerous resources in terms of genome and transcriptome sequences, potential QTLs, genetic variation, molecular markers, association mapping studies, and others. Competitiveness is a cumulative response manifested as morphological, physiological, biochemical or allelochemical response ultimately driven through genetic architecture of a crop and its interaction with environment. Development of wheat competitive cultivar thus requires interdisciplinary approaches and germplasm screening to identify potential donors for competitiveness is an attractive and feasible alternative. For which utilization of landraces and other wild species, already proven to house sufficient genetic heterogeneity, thus poses a competitive advantage. Further, the availability of novel breeding techniques such as rapid generation advance could speed up the development of competitive wheat ideotype.

Associated Bacteria and Their Effects on Growth and Toxigenicity of the Dinoflagellate Prorocentrum lima Species Complex From Epibenthic Substrates Along Mexican Coasts

The dinoflagellate genus Prorocentrum is globally represented by a wide variety of species found upon benthic and/or epiphytic substrates. Many epibenthic Prorocentrum species produce lipophilic polyether toxins, some of which act as potent protein phosphatase inhibitors and tumor-promoters associated with Diarrheic Shellfish Poisoning (DSP). Most members of the P. lima species complex (PLSC) commonly found in the tropics and sub-tropics are toxigenic. Epiphytic and planktonic bacteria co-occur with toxigenic Prorocentrum but reciprocal allelochemical interactions are under-investigated. The aim of the present study was to identify the culturable bacteria collected together with isolates of the PLSC from seagrass (Thalassia testudinum) and macroalgae (Laurencia sp. and Sargassum sp.) along tropical Mexican coasts, and to explore potential species interactions with selected isolates. Twenty-one bacterial genera belonging to Proteobacteria, Actinobacteria and Bacteroidetes were identified by amplification of the 16S rRNA gene marker from nine clonal Prorocentrum cultures, with γ-proteobacteria comprising the dominant class. A positive correlation was found between the bacterial genera associated with two Prorocentrum clones and the esterified toxin analog DTX1a-D8, but there was no apparent correlation between the other PLSC clones and their associated bacteria with the other five DSP toxins detected. No bacteriostatic or allelochemical response was found for cell- and culture medium extracts of five Prorocentrum isolates assayed for bioactivity against Staphylococcus sp. DMBS2 and Vibrio sp. HEL66. Bulk cell-washing of Prorocentrum PA1, followed by growth with antibiotics, was only effective in reducing bacterial load in the initial growth stages, but did not yield axenic cultures or lower bacterial cell densities throughout the culture cycle. Antibiotic treatment did not impair growth or survival of the dinoflagellate, or apparently affect DSP toxin production. There was no significant correlation between Prorocentrum cell volume, growth rate, bacterial cell counts or cellular toxin concentration over the entire time-series culture cycle. Benthic Prorocentrum and associated bacterial communities comprise highly diverse and characteristic microbiomes upon substrates, and among compartments in culture, but this study provides little evidence that allelochemical interactions among Prorocentrum cells and associated bacteria originating from epibenthic substrates play a definable role in growth and toxigenicity.

Temporal variation in positive and negative interactions between marsh herbivores mediated by changes in plant traits

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 634:89-97 (2020) - DOI: https://doi.org/10.3354/meps13187 Temporal variation in positive and negative interactions between marsh herbivores mediated by changes in plant traits Alejandro D. Canepuccia1,*, Daniela Alemany1, Esteban Espinosa Vidal2, M. Fernanda Alvarez3, Oscar O. Iribarne1 1Laboratorio de Ecología, Instituto De Investigaciones Marinas y Costeras (IIMYC), FCEYN, UNMDP-CONICET, CC1260, 7600 Mar del Plata, Argentina 2Center for Strategic Technologies of the Northeastern Region (CETENE), Cidade Universitária, Recife 50740-545, Pernambuco State, Brazil 3Instituto de Limnología ‘Raúl A. Ringuelet’ (ILPLA, CONICET), Universidad Nacional de La Plata, 1900 La Plata, Argentina *Corresponding author: acanepuc@mdp.edu.ar ABSTRACT: Studies on bidirectional benefactor-beneficiary interactions between organisms have generally neglected the importance of this feedback in trophic levels other than plants. The burrowing crab Neohelice granulata aids the development of larvae of the stem-boring moth Haimbachia sp. nov. within the stems of Spartina alterniflora. In our research, we evaluated whether the stem-boring moth subsequently influences crab feeding on these marsh plants. Surveys and experiments in a tidal marsh of the SW Atlantic coast (36°22’S) showed that at the beginning of the stem-boring moth attack there was no difference in crab herbivory between plants with or without larvae of the stem-boring moth. However, after 3.5 mo, crabs foraged more on plants without larvae than on those with larvae. Plant tissue analyses showed a decrease in leaf tissue carbon concentrations in plants with larvae. This change in the nutritional quality of leaves, caused by construction of the stem-boring moth galleries, could explain the segregation in plant use between both herbivores. Unlike an allelochemical response, the non-specificity of the induced nutritional change could impair a wide variety of herbivores regardless of their feeding modes or taxonomic proximity. These effects could propagate bottom-up through the food-web, leading to more diffuse interspecific effects. Thus, here we show how the benefactor-beneficiary feedback between herbivores can be important for the maintenance of species coexistence and the functioning of communities. KEY WORDS: Positive-negative interactions · Indirect interactions · Benefactor-beneficiary relationship · Facilitation · Herbivory · Plant-mediated interactions · Salt marsh · Crabs · Stem-boring moth Full text in pdf format PreviousNextCite this article as: Canepuccia AD, Alemany D, Espinosa Vidal E, Alvarez MF, Iribarne OO (2020) Temporal variation in positive and negative interactions between marsh herbivores mediated by changes in plant traits. Mar Ecol Prog Ser 634:89-97. https://doi.org/10.3354/meps13187 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 634. Online publication date: January 23, 2020 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2020 Inter-Research.

(-)-Loliolide, the most ubiquitous lactone, is involved in barnyardgrass-induced rice allelopathy.

Neighbor detection and allelochemical response are important mediators in plant-plant interactions. Although there is increasing knowledge about plant allelochemicals released in response to the presence of competitors and involved in neighbor-derived signaling, less is known about which signaling chemicals are responsible for the neighbor-induced allelochemical response. Here, we experimentally demonstrate that (-)-loliolide, a carotenoid metabolite, acts as a signaling chemical in barnyardgrass-rice allelopathic interactions. The production of the rice allelochemicals momilactone B and tricin was increased in the presence of five biotypes of barnyardgrass. (-)-Loliolide was found in all the biotypes of barnyardgrass and their root exudates and rhizosphere soils. There were significant positive relationships between rice allelochemicals and (-)-loliolide concentrations across the biotypes of barnyardgrass. Furthermore, (-)-loliolide elicited the production of momilactone B and tricin. Comparative transcriptomic analysis revealed regulatory activity of (-)-loliolide on the diterpenoid and flavonoid biosynthesis pathway. The expression of key genes involved in the biosynthesis of momilactone B (CPS4, KSL4, and MAS) and tricin (CYP75B3 and CYP75B4) was up-regulated by (-)-loliolide. These findings suggest that (-)-loliolide acts as a signaling chemical and participates in barnyardgrass-rice allelopathic interactions. Allelopathic rice plants can detect competing barnyardgrass through the presence of this signaling chemical and respond by increasing levels of their allelochemicals to achieve an advantage for their own growth.

Density-dependent growth response and sensitivity of Meloidogyne incognita to Maerua angolensis and Tabernaemontana elegans: Card model

ABSTRACTCurve-fitting Allelochemical Response Dosage (CARD) computer-based model has proven to be a valuable tool in the definition of dosage response relationships between organisms and various plant extracts. Its use in the explanation of the relationship between Maerua angolensis and Tabernaemontana elegans concentrations and Meloidogyne incognita second-stage juvenile (J2) hatch and mortality has not been reported. The objective of this study was to use the CARD model in the determination of M. incognita sensitivity, density-dependent growth (DDG) patterns and minimum inhibition concentrations of M. angolensis and T. elegans plant extracts on juvenile hatch and mortality. The CARD model quantified concentration ranges of the two plant extracts that could stimulate (Dm − Rh), saturate (Rh − D0) and inhibit (D0 − D100), J2 hatch and mortality. Meloidogyne incognita J2 hatch was moderately sensitive to M. angolensis and T. elegans plant extracts with average sensitivity ranking of 20 and 19 units, respectively. J2 mortalities were moderately sensitive to T. elegans average sensitivity ranking of 15 units, whereas highly sensitive to M. angolensis at 2 units. The minimum juvenile hatch inhibition and lethal concentrations for the two extracts were comparable and very low at 0.07, 0.06 and 0.13, 094 mg mL−1, respectively. In conclusion, the low minimum concentrations for M. incognita J2 hatch inhibition and lethal concentrations of M. angolensis and T. elegans plant extracts and moderate sensitivity values provide substantial evidence of high potency of the two extracts in the potential management of M. incognita.

Response of Bradyrhizobium japonicum nodule variables to cucurbitacin-containing phytonematicides in cowpea (Vigna unguiculata L.) on N-deficient soil

The Curve-fitting Allelochemical Response Data (CARD) had been adopted to develop the non-phytotoxic concentration of phytonematicides, technically referred to as the mean concentration stimulation point (MCSP). The MCSP for cucurbitacin-containing phytonematicides on Bradyrhizobium-nodulated legume crops had not been documented in low-input agricultural farming systems. The objective of this study was to determine the MCSP values of Nemarioc-AL and nemafric-BL phytonematicides on B. japonicum-nodulated cowpea (Vigna unguiculata) on nitrogen-deficient soils. Inoculated cowpea seeds were sown in 20-cm diameter plastic pots containing steam-pasteurised N-deficient loamy soil and Hygromix at 3: 1 (v/v) ratio. Two parallel experiments comprised Nemarioc-AL and Nemafric-BL phytonematicides, each had seven treatments (0, 2, 4, 8, 16, 32 and 64%) and applied once weekly. At 56 days after the treatments, the MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides on cowpea were 5.4 and 6.3%, respectively, with the overall sensitivity (Σk) of one for each phytonematicide. In conclusion, the observed MCSP and Σk values suggested that the two cucurbitacin-containing phytonematicides were suitable for Bradyrhizobium-nodulated cowpea production systems on N-deficient soils.

Plant neighbor detection and allelochemical response are driven by root-secreted signaling chemicals

Plant neighbor detection and response strategies are important mediators of interactions among species. Despite increasing knowledge of neighbor detection and response involving plant volatiles, less is known about how soil-borne signaling chemicals may act belowground in plant–plant interactions. Here, we experimentally demonstrate neighbor detection and allelopathic responses between wheat and 100 other plant species via belowground signaling. Wheat can detect both conspecific and heterospecific neighbors and responds by increasing allelochemical production. Furthermore, we show that (-)-loliolide and jasmonic acid are present in root exudates from a diverse range of species and are able to trigger allelochemical production in wheat. These findings suggest that root-secreted (-)-loliolide and jasmonic acid are involved in plant neighbor detection and allelochemical response and may be widespread mediators of belowground plant-plant interactions.

Non-phytotoxic concentration of cucurbitacin-containing phytonematicides and the overall sensitivities to Swingle citrumelo seedling rootstock

Nemarioc-AL and Nemafric-BL phytonematicides contain cucurbitacins A and B active ingredients, respectively. The major drawback of the two products had been their phytotoxicity to various crops, which was resolved using the Curve-fitting Allelochemical Response Data (CARD) computer-based model, which also provided overall sensitivities (Σk) of the plant to the test phytonematicides. Two of the seven biological indices were adapted to provide the non-phytotoxic concentration, technically referred to as the Mean Concentration Stimulation Point (MCSP)-which is product-specific and crop-specific. The objective of this study was to determine MCSP of Nemarioc-AL and Nemafric-BL phytonematicides on Swingle citrumelo seedling rootstock and the related Σk of the rootstock to the phytonematicides. Six-months-old seedlings were subjected on weekly basis to 0, 2, 4, 8, 16, 32 and 64% for each phytonematicide. At 84 days after the treatments, MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides on seedlings were 2.97 and 5.6%, with Σk values of 3 and 2 units, respectively. In conclusion, both phytonematicides had MCSP and Σk values which suggested that the two products would be suitable for use on Swingle citrumelo seedling rootstock as a supplement for managing nematode population densities in citrus production.

Sensitivities of nematode-inoculated tomato plants to Nemarioc-AL phytonematicide from fresh Cucumis myriocarpus fruit

Costs related to temperature-dependent drying and grinding equipment of Cucumis myriocarpus fruit for preparation of Nemarioc-AL phytonematicide could inherently restrict on-farm preparation of this product, particularly in resource-poor smallholder farming systems. The objective of this study was to determine the overall sensitivities of tomato (Solanum lycopersicon L.) plants and nematodes to Nemarioc-AL phytonematicide produced using fermented crude extracts of C. myriocarpus fresh fruit thereby establishing the feasibility of producing this product on-farm. Uniform five-week-old tomato cv. ‘Floradade’ seedlings were transplanted into plastic pots containing a growing mixture, with treatments 0, 2, 4, 8, 16, 32 and 64% Nemarioc-AL phytonematicide applied weekly on plants inoculated with 3000 Meloidogyne incognita eggs and second-stage juveniles (J2). At 56 days after initiating the treatments, plant and nematode variables were subjected to analysis of variance. Nematode variables over increasing log2 2-transformed concentrations were subjected to lines of the best fit. Nematodes versus increasing concentrations of phytonematicide exhibited negative quadratic relations, with the model for eggs and J2 in roots and soil being explained by 90 and 95% relations, respectively. Plant variables were subjected to the Curve-fitting Allelochemical Response Data (CARD) computer-based model to generate biological indices. The mean concentration stimulation point (MCSP = Dm + Rh/2) was computed 2.79%, with the overall sensitivity (Σk) of four units. In conclusion, Nemarioc-AL phytonematicide from fermented fresh fruit of C. myriocarpus could be used in managing population densities of Meloidogyne species in tomato production without inducing phytotoxity.

English

Bio-pesticides, when used as a post-planting pesticide, are limited by their potential ability to suppress the pest and their degree of phytotoxicity. Baseline information on the suitability of fermented crude extracts (FCE) of Cucumis africanus fruit as a post-planting bio-nematicide was determined on Meloidogyne incognita and growth of tomato in pot trials. Seedlings were inoculated with 1,130 eggs and juveniles/pot, while FCE were applied weekly at 0, 10, 20, 30, 40, 50 and 60% dilutions. At harvest, nematode and plant data were subjected to analysis of variance and the curve-fitting allelochemical response data (CARD) computer-based model, respectively. Relative to inoculation level, final nematode population density (Pf) at the same level of inoculation was reduced, while increasing dosages had no effect on Pf and reproductive factor values. Since increasing dosages had no effect on Pf, the material could possibly still reduce this variable when applied below 10% dilutions. Dosages used were phytotoxic to tomato plants, but CARD model demonstrated that the material stimulated plant growth at dosages below 10%. In conclusion, baseline information from CARD model suggested that FCE from C. africanus fruit have the potential to serve as a bio-nematicide and bio-fertiliser on tomato provided the material was applied below 10% dilutions. Key words : Cucumis africanus , bionemagation, effective microbe organisms, ground leaching technology, root-knot nematode.

Interactive Effects of Simulated Nitrogen Deposition and Altered Precipitation Patterns on Plant Allelochemical Concentrations

Global environmental change alters the supply of multiple limiting resources that regulate plant primary and secondary metabolism. Through modifications in resource availability, acquisition, and allocation, global change is likely to influence plant chemical defenses, and consequently species interactions that are mediated by these compounds. While many studies focus on individual global change factors, simultaneous changes in abiotic factors may interact to influence plant allelochemicals. In this study, we examined the individual and interactive effects of nitrogen enrichment and altered precipitation patterns on chemical defense compounds (iridoid glycosides) of an invasive plant, Linaria dalmatica. Plants were grown from seed in native mixed-grass prairie for 2 years. Nitrogen and water treatments were applied in each growing season over this period. Results indicate that soil water and nitrogen availability interact to shape plant chemical defense concentrations in L. dalmatica. Nitrogen addition decreased iridoid glycoside concentrations by approximately 25% under reduced water availability, increased concentrations by 37% in ambient water plots, and had no effect on these chemical defenses for plants growing under augmented water supply. Thus, results show differing patterns of allelochemical response to nitrogen enrichment, with respect to both the magnitude and direction of change, depending on water availability. Our study demonstrates the importance of examining multiple environmental factors in order to predict potential changes in plant chemical defenses with climate change.

Mean Dosage Stimulation Range of Allelochemicals from Crude Extracts of Cucumis africanus Fruit for Improving Growth of Tomato Plant and Suppressing Meloidogyne incognita Numbers

Successful utilisation of allelochemicals in management of plant-parasitic nematodes depends on their degree of phytotoxicity. Conventional methods of determining phytotoxicity are tedious, with inconsistent results. Plants respond to increased dosages of allelochemicals in a density-dependent growth pattern, which allows the use of the Curve-fitting Allelochemical Response Data computer-based model to determine the mean dosage stimulation range of used allelochemicals. The CARD modelling was used to determine the stimulation range of fermented dried crude extracts of wild cucumber (Cucumis africanus) fruit for improving growth of tomato (Solanum lycopersicon) plants, each infested with 1500 eggs and juveniles of the southern root-knot (Meloidogyne incognita) nematode. Dilutions at 0, 2, 4, 8, 16, 32 and 64% were applied weekly through irrigation system. At 56 days after treatment, CARD demonstrated density-dependent growth patterns as dosages increased. The mean dosage stimulation range of diluted fermented crude extracts, computed from CARD biological indices, was 2.64% dilution for tomato plant. Since at 2% dilution, the material reduced final nematode population density of M. incognita by 90%. The 2.64% was suitable for stimulation of tomato plant and suppression of nematode numbers.

Modelling responses of maize, millet and sorghum seedlings to crude extracts of Cucumis myriocarpus fruit as pre-emergent bio-nematicide

Biological indices generated using the CARD (curve-fitting allelochemical response data) model may be useful in crop-bio-nematicide interactions since they provide information related to the stimulation dosage of the material to the crops. The objective of this study was to determine: (1) Whether selected crops in the Gramineae family respond to crude extracts of Cucumis myriocarpus fruit in density-dependent patterns, and (2) the appropriate dosage of crude extracts of C. myriocarpus fruit when used as a pre-plant bio-nematicide in Gramineae family. Separate studies using three maize, millet and sorghum were conducted under greenhouse conditions with ten treatments (0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00 and 2.25 g material/pot), arranged in randomised complete block design, with five replicates. At harvest, 18 days after treatment, the CARD model demonstrated that the responses of plant organs when regressed on a series of crude extracts of C. myriocarpus fruit stimulate exhibited the density-dependent growth patterns, with various organs having different sensitivities to the material. The integrated sensitivity of the measured variables showed that the test crops differed with increasing order of sensitivity to the test material with increasing order of sensitivity to the material being sorghum > maize > millet. Estimated mean dosage response for stimulation (MDRS) for maize, millet and sorghum being 1.13, 0.86 and 1.12 g, respectively. In conclusion, at low dosages crude extracts of C. myriocarpus fruit stimulate plant growth and, therefore, have the potential for use as pre-emergent bio-nematicide in maize, millet and sorghum production. Key words: Biological indices, CARD model, density-dependent growth patterns, maize, millet, sorghum.

On the allelochemical potency of the marine dinoflagellate Alexandrium ostenfeldii against heterotrophic and autotrophic protists

Three strains of the marine dinoflagellate Alexandrium ostenfeldii of different geographic origin were tested for their short-term deleterious effects on a diversity of marine protists. All A. ostenfeldii strains were capable of eliciting an apparent allelochemical response, but the various protistan target species were differentially affected. Protists that were negatively affected by exposure to cells of A. ostenfeldii and associated extracellular metabolites comprised both autotrophs (Rhodomonas sp., Dunaliella salina, Thalassiosira weissflogii) and heterotrophs (Oxyrrhis marina, Amphidinium crassum, Rimostrombidium caudatum). Observed effects included immobilisation (e.g. of O. marina), morphological changes (e.g. in D. salina) and/or aberrant behaviour (e.g. of R. caudatum), mainly as preliminary stages of cell lysis. Immobilization and lytic effects against O. marina were strongly dependent on A. ostenfeldii cell concentrations. Effects also differed substantially among strains and different batch cultures of the same strain. Values of EC50, defined as the A. ostenfeldii cell concentration causing lysis of 50% of O. marina cells, ranged from 0.3 to 1.9 � 10 3 mL 21 , depending on the A. ostenfeldii strain. The autotrophic dinoflagellate Scrippsiella trochoidea reacted to exposure to A. ostenfeldii cells by formation of temporary (ecdysal) cysts, whereas, in contrast, the flagellates Emiliania huxleyi and Prymnesium parvum and the ciliate Strombidium sp. were relatively refractory or even unaffected. As long as cells did not lyse, the fluorescence yield of target autotrophs, estimated by pulse-amplitude modulation fluorometry, did not significantly change during the first 3 h of incubation, suggesting that allelochemicals produced by A. ostenfeldii caused no shortterm negative effects on the photosynthetic apparatus. Overall, the allelochemical responses of target species showed no obvious relationship to cell quota or extracellular concentrations of either toxic macrocyclic imines (spirolides) or tetrahydropurine neurotoxins (saxitoxin and analogues) produced by various strains of A. ostenfeldii. Instead, the potency of A. ostenfeldii, eliciting immobilization and lytic species-specific responses in potential predators and competitors, is consistent with the existence of an allelochemical mechanism unrelated to the bioactivity of known phycotoxins of the genus Alexandrium.

Implementation of Card: Curve-Fitting Allelochemical Response Data

Bioassay techniques are essential methods used to study the effects of allelochemicals on plant processes. It is often observed that the biological processes are stimulated at low allelochemical concentrations and inhibited as the concentrations increase. Liu et al., (2003) developed a simple model to fit this type of allelochemical response data. Based on the model, CARD (curve-fitting allelochemical response data) was developed as a Windows based program that can be used to fit a stimulation-inhibition response data. An example of using CARD is given.

Aggregation facilitates larval growth in the neotropical nymphalid butterfly Chlosyne janais

1. Larvae of Chlosyne janais (Lepidoptera: Nymphalidae) feed gregariously as early instars on the shrub Odontonema callistachyum (Acanthaceae). During the fourth instar, aggregations break up and larvae feed as solitary individuals.2. The hypothesis that aggregation increases growth rate was tested by raising larvae on intact plants in the field in different group sizes and measuring their daily growth.3. There was a striking effect of group size on larval growth whereby larvae more than doubled their weight gain by feeding in large rather than small aggregations on intact plants in the field.4. This group‐feeding advantage was lost altogether if larvae were raised on excised leaves in the laboratory, suggesting that large aggregations may facilitate growth either by inducing a nutrient sink or by overwhelming an induced allelochemical response in the plant.5. Although larval survival was higher in cages that excluded enemies than in exposed aggregations, there was no influence of group size (experimentally manipulated) on short‐term survival in the field. However, there was a weak positive relationship between short‐term survival and the size of naturally occurring larval aggregations in the field. These data provide mixed support for the notion that gregarious feeding promotes defence against natural enemies.6. Although the group defence hypothesis warrants further investigation, feeding facilitation is clearly an important factor contributing to the aggregation behaviour of C. janais larvae.