Phenolics are one of the many secondary metabolites implicated in allelopathy To establish that allelopathy functions in a natural ecosystem, the allelopathic bioassay must be ecologically realistic so that responses of appropriate bioassay species are determined at relevant concentrations It is important to isolate, identify, and characterize phenolic compounds from the soil However, since it is essentially impossible to simulate exact field conditions, experiments must be designed with conditions resembling those found in natural systems It is argued that allelopathic potential of phenolics can be appreciated only when we have a good understanding of 1) species responses to phenolic allelochemicals, 2) methods for extraction and isolation of phenolic allelochemicals, and 3) how abiotic and biotic factors affect phenolic toxicity

Plant phenolics in allelopathy

Current evidence illustrates the significance of soil microbes in influencing the bioavailability of allelochemicals. This review discusses (i) the significance of soil microorganisms in influencing allelopathic expression, (ii) different ways of avoiding microbial degradation of putative allelochemicals, and (iii) the need of incorporating experiments on microbial modification of allelochemicals in laboratory bioassays for allelopathy. Several climatic and edaphic factors affect the soil microflora; therefore, allelopathy should be assessed in a range of soil types. Allelopathy can be better understood in terms of soil microbial ecology, and appropriate methodologies are needed to evaluate the roles of soil microorganisms in chemically-mediated interactions between plants.

Soil microorganisms: An important determinant of allelopathic activity

Allelopathy can be defined as chemical interactions between and among both plants and microorganisms via releases of biologically active chemical compounds into the environment. During the past three decades this scientific field has received growing attention from soil scientists, microbiologists, ecologists, plant physiologists, biochemists, botanists, weed scientists, agronomists, and natural product chemists. Although a few studies are acknowledged to have demonstrated probable allelopathy in nature, many appeared limited to in vitro circumstances. This difficulty reflects the complexity of allelopathic interactions. Allelopathic effects are often modified by additional biotic and abiotic stress factors, uncertain meteorological events, or physical, chemical, and biological soil factors, all of which can influence the residence time, persistence, concentration, and fate of allelopathic compounds in the environment. Special emphasis is given to an overview of the allelopathic activities of weed and crop species, especially via crop residues in the agroecosystem, and to consideration of the biotic and abiotic factors which influence the expression of Allelopathy A brief discussion of secondary metabolites with allelopathic activities and of the mechanisms of action of allelopathic compounds is also provided. The allelopathic potential of certain weed and crop species can influence the growth and distribution of associated weed species and the yield of desired plants, and allelopathy has been employed successfully in biocontrol programs focusing on control of problematic weeds and plant diseases. Thus, it plays an important role in an agroecosystem and it is clear that a better understanding of allelopathy can help both in crop improvement and in developing more sustainable agriculture

Allelopathy: Principles, Procedures, Processes, and Promises for Biological Control

Background: Allelopathy (negative, plant-plant chemical interactions) has been largely studied as an autecological process, often assuming simplistic associations between pairs of isolated species. The growth inhibition of a species in filter paper bioassay enriched with a single chemical is commonly interpreted as evidence of an allelopathic interaction, but for some of these putative examples of allelopathy, the results have not been verifiable in more natural settings with plants growing in soil. Methodology/Principal findings: On the basis of filter paper bioassay, a recent study established allelopathic effects of mtyrosine, a component of root exudates of Festuca rubra ssp. commutata. We re-examined the allelopathic effects of mtyrosine to understand its dynamics in soil environment. Allelopathic potential of m-tyrosine with filter paper and soil (nonsterile or sterile) bioassays was studied using Lactuca sativa, Phalaris minor and Bambusa arundinacea as assay species. Experimental application of m-tyrosine to non-sterile and sterile soil revealed the impact of soil microbial communities in determining the soil concentration of m-tyrosine and growth responses. Conclusions/Significance: Here, we show that the allelopathic effects of m-tyrosine, which could be seen in sterilized soil with particular plant species were significantly diminished when non-sterile soil was used, which points to an important role for rhizosphere-specific and bulk soil microbial activity in determining the outcome of this allelopathic interaction. Our data show that the amounts of m-tyrosine required for root growth inhibition were higher than what would normally be found in F. rubra ssp. commutata rhizosphere. We hope that our study will motivate researchers to integrate the role of soil microbial communities in bioassays in allelopathic research so that its importance in plant-plant competitive interactions can be thoroughly evaluated.

Taking ecological function seriously: soil microbial communities can obviate allelopathic effects of released metabolites.

Bioassays are an integral part of allelopathy research. The unsuitability of laboratory bioassays to explain field situations is discussed previously. In this article, we discuss progress in bioassay experimental design and several unresolved problems associated with research on allelopathy. The objectives of this article are to discuss problems related to (1) collection of allelopathic material for bioassay, (2) allelochemical quantification in bioassays, (3) selection of concentration of allelochemicals in bioassay, (4) selection of appropriate control, (5) interaction between allelochemicals and other substances, and (6) in situ allelochemical bioassays. We concluded that new experimental designs for in situ bioassay are needed that can account for the large number of confounding factors in a complex field environment, and can be linked to physiological monitoring of target species and biochemical monitoring of the growth medium. Referee: Dr. Stella Elakovich, Dept. of Chemistry and Biochemistry, Unive...

Ursula Kupas

Papers

Degradation of juglone by Pseudomonas putida J 1