The Allelopathic Potentialities of Acacia nilotica and Eucalyptus rostrata on Monocot (Zea mays L.) and Dicot (Phaseolus vulgaris L.) Plants

Phytotoxic effects of Acacia saligna dry leachates on germination, seedling growth, photosynthetic performance, and gene expression of economically important crops

The influence of dry leachates of Acasia saligna was tested on the seedling growth, photosynthesis, biochemical attributes, and gene expression of the economically important crops, including wheat (Triticum aestivum L.), radish (Raphanus sativus L.), barley (Hordeum vulgare L.) and arugula (Eruca sativa L.). Different concentrations (5%, 10%, 15%, 20%, and 25%) of stem extract (SE) and leaf extract (LE) of A. saligna were prepared, and seedlings were allowed to grow in Petri plates for 8 days. The results showed that all plant species exhibited reduced germination rate, plant height, and fresh and dry weight due to leachates extracts of A. saligna. Moreover, the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), exhibited differential regulation due to the extract treatment. The SOD was increased with increasing the concentration of extracts, while CAT and APX activities were decreased with increasing the extract concentrations. In addition, leachate extract treatment decrease chlorophyll content, photosynthesis, PSII activity, and water use efficiency, with evident effects at their higher concentrations. Furthermore, the content of proline, sugars, protein, total phenols, and flavonoids were reduced considerably due to leachates extract treatments. Furthermore, seedlings treated with high concentrations of LE increased the expression of genes. The present results lead to the conclusion that A. saligna contains significant allelochemicals that interfere with the growth and development of the tested crop species and reduced the crops biomass and negatively affected other related parameters. However, further studies are suggested to determine the isolation and purification of the active compounds present in A. saligna extracts.

Allelopathy and its application as a weed management tool: A review

Weeds are a serious threat to crop production as they interfere with the crop growth and development and result in significant crop losses. Weeds actually cause yield loss higher than any other pest in crop production. As a result, synthetic herbicides have been widely used for weed management. Heavy usage of synthetic herbicides, however, has resulted in public concerns over the impact of herbicides on human health and the environment. Due to various environmental and health issues associated with synthetic herbicides, researchers have been exploring alternative environmentally friendly means of controlling weed. Among them, incorporating allelopathy as a tool in an integrated weed management plan could meaningfully bring down herbicide application. Allelopathy is a biological phenomenon of chemical interaction between plants, and this phenomenon has great potential to be used as an effective and environmentally friendly tool for weed management in field crops. In field crops, allelopathy can be applied through intercropping, crop rotation, cover crops, mulching and allelopathic water extracts to manage weeds. Accumulating evidence indicates that some plant species possess potent allelochemicals that have great potential to be the ecofriendly natural herbicides. This review is intended to provide an overview of several allelopathic species that release some form of the potent allelochemical with the potential of being used in conventional or organic agriculture. Further, the review also highlights potential ways allelopathy could be utilized in conventional or organic agriculture and identify future research needs and prospects. It is anticipated that the phenomenon of allelopathy will be further explored as a weed management tool, and it can be a part of a sustainable, ecological, and integrated weed management system.

Allelopathic Potential of Aqueous Extract from Acacia melanoxylon R. Br. on Lactuca sativa

We studied the polyphenol (phenolic compounds and flavonoids) composition and allelopathic effects of Acacia melanoxylon R. Br. aerial foliage aqueous extract (0%, 25%, 50%, 75% and 100%) on the seedling growth and plant biomass of the general biotest species, lettuce (Lactuca sativa). Mean leaf fresh weight, leaf dry weight, root fresh weight and root dry weight were decreased following exposure to Acacia aerial foliage, flowers aqueous extract (AFE) and phyllodes aqueous extract (APE) after 6 days. The reduction in plant dry biomass was more than 50% following treatment with AFE. The decrease in mean root length was approximately 37.7% and 29.20% following treatment with Acacia flowers extract (AFE) at 75% and 100% concentration, respectively. Root dry weight of L. sativa was reduced by both flowers and phyllodes extract. The reduction of protein contents in lettuce leaves following Acacia foliage extract proved that both AFE and APE exhibit polyphenols that causes the toxicity which led to decrease in leaf protein contents. High-Performance Liquid Chromatography (HPLC) was employed to analyze the A. melanoxylon flowers and phyllodes. A total of 13 compounds (accounting for most abundant compounds in flowers and phyllodes) include different flavonoids and phenolic compounds. The phytochemical compounds detected were: Gallic acid, protocatechuic acid, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, vanillic acid, syringic acid, p-coumaric acid, and ferulic acid. The major flavonoid compounds identified include rutin, luteolin, apigenin, and catechin. Allelopathic effects of flower and phyllodes extracts from A. melanoxylon may be due to the presence of above compounds identified by HPLC analysis.

Allelopathic Potentials of <I> Artrmisia monosperma</I> and <I> Thymus vulgaris</I> on Growth and Physio-Biochemical Characteristics of Pea Seedlings

BACKGROUND AND OBJECTIVE

Several medicinal plants are reported as having allelochemicals potentials and favorable results have been obtained in this regard. The present investigation aimed to evaluate the effect of different concentrations of leaf aqueous extract of two medicinal plants, Artrmisia monosperma and Thymus vulgaris on growth criteria, physio-biochemical attributes and antioxidant enzyme activities of pea (Pisum sativum L.) seedlings.

MATERIALS AND METHODS

Germination of pea was performed in Petri dishes under different concentrations (0, 2, 4, 6, 8 and 10%) of leaf aqueous extracts of the two medicinal plants collected from natural habitats in Saudi Arabia. At the end of experiment (10 days), the growth and physio-biochemical characteristics of pea seedlings were measured. The data were statistically analyzed by one-way ANOVA analysis of variance using SPSS program.

RESULTS

Leaf aqueous extracts of A. monosperma and T. vulgaris reduced germination capability, shoot and root length, total free amino acids and proline content. Contrariwise, there was an increase in carbohydrates, proteins, K+, Ca2+ and the activity of antioxidant enzymes. Lipid peroxidation and H2O2 contents were significantly enhanced with increasing concentrations of both extracts. The highest inhibitory or stimulatory effects of leaf aqueous extract were observed at concentrations 8 and 10%. T. vulgaris was more effective than A. monosperma.

CONCLUSION

This investigation indicated that the two medicinal plants had allelopathic compounds with strong potential, which may play important role in weed control and used as an alternative of chemical compounds. The aqueous extract of T. vulgaris has allelopathic potential more than A. monosperma and could be evaluated as an allelopathic species.

Phytotoxical effect of Lepidium draba L. extracts on the germination and growth of monocot (Zea mays L.) and dicot (Amaranthus retroflexus L.) seeds

Laboratory experiments were performed to determine phytotoxic potentials of white top (Lepidium draba) methanol extracts (root, stem and leaf) on germination and early growth of corn (Zea mays) and redroot pigweed (Amaranthus retroflexus). Furthermore, the effects of different methanol extracts of L. draba on the phytohormone (indole-3-acetic acid (IAA), gibberellic acid (GA), abscisic acid (ABA) and zeatin) levels of corn and redroot pigweed were investigated. It was observed that all concentrations of methanol extracts of root, stem and leaf of L. draba inhibited germination, radicle and plumule elongation when compared with the respective controls. Besides this, the degree of inhibition was increased in concert with increasing concentrations of extracts used. On the other hand, phytohormone levels changed with the application of different extract concentrations. Comparing with the control, the GA levels significantly decreased while the ABA levels increased in all the application groups. Zeatin and IAA levels showed changes depending upon the applied extracts and concentrations.

Composição da fauna de formigas (Hymenoptera: Formicidae) de serapilheira em florestas semidecídua e de Eucalyptus spp., na região sudeste do Brasil

Este estudo teve como objetivo avaliar a composição da fauna de formigas de serapilheira em áreas de floresta semidecídua com plantio de eucalipto sem manejo durante diferentes períodos. Foram estudadas quatro áreas, sendo três com eucalipto e uma formada por vegetação nativa; todas estão localizadas no município de Rio Claro (SP), sudeste do Brasil. Em cada área foram coletadas 100 amostras de 1 m² de serapilheira, abrangendo os períodos seco e chuvoso da região. Cada amostra foi submetida a extratores do tipo mini-winkler, onde permaneceram por 48 horas. Foram amostradas 58.410 formigas, distribuídas em 10 subfamílias, 42 gêneros e 120 morfoespécies/espécies. Destas, 85 espécies foram encontradas na floresta semidecídua e 84 na floresta de Eucalyptus tereticornis com 100 anos sem manejo. Já nas florestas de E. tereticornis e E. urophylla com 22 anos sem manejo foram encontradas 73 e 56 espécies, respectivamente. Baseando-se em estudos anteriores, este inventário proporcionou o conhecimento de mais 16 gêneros e 24 espécies para a região estudada, sendo três exóticas. A ordenação das amostras com o escalonamento multidimensional não-métrico (NMDS) indicou diferença na similaridade entre as amostras das áreas, especialmente àquelas pertencentes à floresta de E. urophylla. Além do período sem manejo, a presença de substâncias alelopáticas na serapilheira pode estar interferindo no número de espécies e nas comunidades. Os resultados demonstram a importância das florestas abandonadas de eucaliptos para a manutenção da diversidade de formigas em uma região em que a vegetação nativa é escassa.

Allelopathy--a natural alternative for weed control

Allelopathy studies the interactions among plants, fungi, algae and bacteria with the organisms living in a certain ecosystem, interactions that are mediated by the secondary metabolites produced and exuded into the environment. Consequently, allelopathy is a multidisciplinary science where ecologists, chemists, soil scientists, agronomists, biologists, plant physiologists and molecular biologists offer their skills to give an overall view of the complex interactions occurring in a certain ecosystem. As a result of these studies, applications in weed and pest management are expected in such different fields as development of new agrochemicals, cultural methods, developing of allelopathic crops with increased weed resistance, etc. The present paper will focus on the chemical aspects of allelopathy, pointing out the most recent advances in the chemicals disclosed, their mode of action and their fate in the ecosystem. Also, attention will be paid to achievements in genomics and proteomics, two emerging fields in allelopathy. Rather than being exhaustive, this paper is intended to reflect a critical vision of the current state of allelopathy and to point to future lines of research where in the authors' opinion the main advances and applications could and should be expected.