Sonia Cristina Juliano Gualtieri

Phytotoxins from Tithonia diversifolia

Tithonia diversifolia (Mexican sunflower) is a dominant plant of the Asteraceae family, which suggests it produces allelochemicals that interfere with the development of surrounding plants. The study described herein was conducted to identify the compounds that have phytotoxic activity in T. diversifolia extracts. Ethyl acetate extracts of the leaves, stems, and roots showed significant inhibition of wheat coleoptile growth, and the leaf extract had similar inhibitory effects to a commercial herbicide. Fourteen compounds, 12 of which were sesquiterpene lactones, have been isolated. Two sesquiterpene lactones are reported for the first time and were isolated as an inseparable mixture of 8β-O-(2-methylbutyroyl)tirotundin (4) and 8β-O-(isovaleroyl)tirotundin (5). Their structures were determined by spectroscopic analysis, including NMR techniques and mass spectrometry. The sesquiterpene lactones 1β-methoxydiversifolin (6), tagitinin A (7), and tagitinin C (8) were the major products identified. These compounds were active on etiolated wheat coleoptiles, seed germination, and the growth of STS and weeds. The phytotoxic activity shown by these sesquiterpene lactones indicates that they are the compounds responsible for the activity exhibited by the initial extracts.

Interspecific variation in the allelopathic potential of the family Myrtaceae

Allelopathy is a type of biotic interference wherein a plant releases bioactive metabolites into an environment, thereby affecting the adjacent biota. Stressful environments stimulate the production of these metabolites. The present study tests the novel weapons hypothesis, which postulates that species belonging to the same genus and from the same environment have similar allelopathic effects. The aim of this study was to assess the allelopathic effects that the aqueous leaf extracts of 15 species belonging to five genera of the Myrtaceae family have on the seed germination and initial seedling growth of lettuce (Lactuca sativa L.), tomato (Solanum lycopersicum L.) and onion (Allium cepa L.). Germination rates, average germination times, informational entropy of germination and allelopathic effects, as quantified with a response index, were calculated. A taxonomic distance matrix based on Gower dissimilarity and a Euclidean distance matrix were constructed. The results revealed that all extracts from donor species significantly increased average germination time or reduced the germination rate of eudicotyledonous plant species. The only extracts that showed no effect on monocotyledonous seeds were those of Campomanesia pubescens O. Berg and Psidium cinereum Mart. We conclude that eudicotyledonous and monocotyledonous plants were both significantly affected by the presence of all extracts tested. Our results make it clear that each species behaves distinctly in relation to allelopathic activity, with no apparent grouping by genus or subtribe. Therefore, the hypothesis was rejected, because plants from the same environment and with taxonomic proximity do not necessarily display similar production of secondary metabolites.

Effect of Serjania lethalis ethanolic extract on weed control

The objective of this study was to evaluate the effect of the ethanolic extract of Serjania lethalis leaves and stems on the diaspore germination and seedling growth of wild poinsettia (Euphorbia heterophylla) and barnyardgrass (Echinochloa crus-galli). The crude ethanolic extract was prepared from 100 g of dry plant material dissolved in 500 ml of ethanol. The extracts were solubilized in a buffer solution containing dimethyl sulfoxide (DMSO) at concentrations of 10.0, 7.5, 5.0 and 2.5 mg mL-1. The effect of these extracts was compared with herbicide oxyfluorfen in bioassays. The ethanolic extracts of S. lethalis leaves and stems inhibited the germination and seedling growth of barnyardgrass and wild poinsettia in a concentration-dependent manner. The reduction in the root length of E. heterophylla seedlings might be attributed to the reduced elongation of metaxylem cells. The phytotoxicity of the extracts ranged according to the receptor species, and for some variables, the inhibitory effect was similar, and even superior, to that of the commercial herbicide. Thus, S. lethalis extracts might be a promising alternative for sustainable weed management.

Estudo fitoquímico de folhas de Solanum lycocarpum A. St.-Hil (Solanaceae) e sua aplicação na alelopatia

Solanum lycocarpum A.St.-Hil (Solanaceae) is a typical shrub in the Cerrado of central Brazil. The allelopathic activity of aqueous extracts of the leaves and fruits of this species has already been proven in previous studies. The goal of this work was to verify the allelopathic activity of different leaf extracts of S. lycocarpum on the germination and growth of four target species. The leaves were collected, dried, triturated and submitted to two distinct methods of extraction: 1- liquid-liquid (ethyl acetate and dichloromethane) from the aqueous extract and 2- with solvents of increasing polarities (hexane, dichloromethane, ethyl acetate, acetone, methanol and water) directly from the leaves. Each extraction was made with ultrasound equipment for one hour, filtered and evaporated. From these extracts, solutions of 800, 400 and 200 ppm were prepared, and water and Logran® were used as positive and negative controls, respectively. Each solution, as well as the controls, was dissolved in DMSO for the bioassays. The target species used were lettuce, watercress, tomato and onion. To each plate, 20 seeds were added and 1 mL of the tested solutions (with 4 repetitions). The plates were incubated at 25 oC without light, and the shoots and roots of the seedlings were then measured and the percentage of germination and the inhibition of each extract were calculated. Tomato was the most sensitive to the extracts, followed by watercress, onion and lettuce. The extracts with stronger activity were AcOEt, acetone and the liquid-liquid extraction, indicating the fractions that may contain the active principles of the leaves in this species.

Allelopathic potential of Rapanea umbellata leaf extracts.

The stressful conditions associated with the Brazilian savanna (Cerrado) environment were supposed to favor higher levels of allelochemicals in Rapanea umbellata from this ecosystem. The allelopathic potential of R. umbellata leaf extracts was studied using the etiolated wheat coleoptile and standard phytotoxicity bioassays. The most active extract was selected to perform a bioassay‐guided isolation, which allowed identifying lutein (1) and (−)‐catechin (2) as potential allelochemicals. Finally, the general bioactivity of the two compounds was studied, which indicated that the presence of 1 might be part of the defense mechanisms of this plant.

Allelopathic interference of Sapindus saponaria root and mature leaf aqueous extracts on diaspore germination and seedling growth of Lactuca sativa and Allium cepa

Sapindus saponaria (soapberry) is a species that presents a great diversity of chemical compounds, such as saponins; however, few studies have examined the allelopathic effect of this species. Therefore, this study provides an evaluation of the allelopathic potential of aqueous extracts of the roots and mature leaves of S. saponaria on the germination of diaspores and seedlings growth of lettuce (Lactuca sativa) and onion (Allium cepa). The aqueous extract was prepared in the proportion of 100 g of dry plant material in 1,000 mL of distilled water (a concentration of 10% w v-1), and diluted with distilled water to 7.5, 5.0 and 2.5% concentrations. The mature leaf extracts caused delay and decrease in the germination process of the lettuce and onion diaspores, with inhibitory effect concentration-dependent, while the root extracts showed no allelopathic effects on the germination process. Both extracts caused abnormalities and inhibited the growth of shoot and root seedlings.

Allelopathy of Bracken Fern (Pteridium arachnoideum): New Evidence from Green Fronds, Litter, and Soil

The neotropical bracken fern Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae) is described as an aggressive pioneer plant species. It invades abandoned or newly burned areas and represents a management challenge at these invaded sites. Native to the Atlantic Forest and Cerrado (Tropical Savanna) Brazilian biomes, P. arachnoideum has nevertheless become very problematic in these conservation hotspots. Despite some reports suggesting a possible role of allelopathy in this plant’s dominance, until now there has been little evidence of isolated and individually identified compounds with phytotoxic activities present in its tissues or in the surrounding environment. Thus, the aim of this study was to investigate the allelopathic potential of P. arachnoideum by isolating and identifying any secondary metabolites with phytotoxic activity in its tissues, litter, and soil. Bioguided phytochemical investigation led to the isolation and identification of the proanthocyanidin selligueain A as the major secondary compound in the green fronds and litter of this fern. It is produced by P. arachnoideum in its green fronds, remains unaltered during the senescence process, and is the major secondary compound present in litter. Selligueain A showed phytotoxic activity against the selected target species sesame (Sesamum indicum) early development. In particular, the compound inhibited root and stem growth, and root metaxylem cell size but did not affect chlorophyll content. This compound can be considered as an allelochemical because it is present in the soil under P. arachnoideum patches as one of the major compounds in the soil solution. This is the first report of the presence of selligueain A in any member of the Dennstaedtiaceae family and the first time an isolated and identified allelochemical produced by members of the Pteridium species complex has been described. This evidence of selligueain A as a putative allelochemical of P. arachnoideum reinforces the role of allelopathy in the dominance processes of this plant in the areas where it occurs.

Phytotoxic potential of young leaves from Blepharocalyx salicifolius (Kunth) O. Berg (Myrtaceae)

The loss of leaves by plant species found in the Cerrado (Brazilian savanna) is an energetically expensive process due to adverse environmental conditions and predation by herbivory. The mature leaves have adaptations which minimize these events. However, the young individuals lack these structures and produce high leaf concentrations of secondary metabolites as a form of protection. These compounds can be used in bioprospection of natural herbicides. Thus, this study aimed to evaluate the phytotoxicity of hexane, ethyl acetate and aqueous extracts of young leaves from Blepharocalyx salicifolius (Kunth) O. Berg on the elongation of wheat coleoptiles (Triticum aestivum L.) and evaluate the potential phytotoxic of ethyl acetate extract on germination, growth and cell size of metaxylem of sesame (Sesamum indicum L.) seedlings. The hexane and ethyl acetate extracts inhibited the elongation of wheat coleoptiles at all concentrations; however, the most promising results were observed in coleoptile fragments treated with the ethyl acetate extract. This treatment changed the mean germination time and the synchrony of sesame seeds, inhibited the growth of shoots and roots, reduced the dry weight of seedlings, led to abnormalities in the seedlings and reduced the length of the metaxylem cells in the sesame seedlings. These results demonstrated the phytotoxic potential of young leaf extracts of B. salicifolius and the high phytotoxicity of the ethyl acetate extract in the initial development of S. indicum.

Efeito alelopático do fruto de Sapindus saponaria na germinação e na morfologia de plântulas daninhas e de hortaliças

O objetivo deste estudo foi avaliar o potencial alelopatico do extrato aquoso de frutos de Sapindus saponaria (sabao-de-soldado) na germinacao de diasporos e na morfologia de plântulas de Lactuca sativa (alface), Allium cepa (cebola), Echinochloa crus-galli (capim-arroz) e Ipomoea grandifolia (corda-de-viola). O extrato aquoso dos frutos foi preparado na proporcao de 100 g de material vegetal fresco para 1.000 mL de agua destilada, produzindo-se a concentracao de 10%. A partir dele, foram feitas diluicoes em agua destilada para 7,5, 5,0 e 2,5%. O extrato do fruto Sapindus saponaria evidenciou potencialidades alelopaticas tanto sobre as especies de hortalicas quanto sobre as de plantas daninhas. O efeito inibitorio sobre o processo de germinacao dos diasporos e morfologia das plântulas de alface, cebola, capim-arroz e corda-de-viola foi dependente da concentracao. Os resultados mostram o potencial do extrato proveniente dos frutos de Sapindus saponaria como um herbicida a ser utilizado em praticas de agricultura sustentavel.

Oleoresin yield of Pinus elliottii Engelm seedlings

Pinus elliottii is a fast-growing conifer well adapted to southern Brazil, used for wood fiber and resin production. Oleoresin production is part of the plants defense systems and is induced by ethylene, which production is stimulated by hypoxic conditions. The experiment was designed with the goal of verifying whether one year-old plants had measurable oleoresin yield and if flooding led to increased oleoresin production. There was an increase of 78% in oleoresin production after 14 to 21 days of flooding and plants with larger stem diameters were more productive.