Chapter 1. LABORATORY BIOASSAYS IN ALLELOPATHY

NARWAL, S. S.; SAMPIETRO, D. A.; CATALÁN, C. A. N.

Plant Bioassays.

Studium Press, LLC

Lugar: Houston, USA; Año: 2009; p. 3 - 20

The science of allelopathy as defined by Molisch (1937) includes inhibitory as well as stimulatory effects of one plant on another, including microorganisms. After Molisch and till 1970, allelopathy commonly referred to negative interactions between the plants. Thereafter, the definition of Molisch has been followed. The stimulatory or inhibitory effects of one plant on another are mediated through release of allelochemicals. There is increasing concern for potential use of these substances in sustainable agriculture, especially in underdeveloped countries, because they may constitute an alternative to synthetic polluting pesticides currently employed in crop protection. Interest in allelopathy unfortunately has been accompanied with inconsistencies in the methodology applied to identify and exploit this phenomenon in modern agriculture (Dhawan and Narwal, 1995). Establishing the presence of a chemical within a plant and use of this substance in a formulated form to control plant growth is not the same as the study of the possible involvement of a plant material in an allelopathic interaction. Although standard procedures for isolation and characterization of plant allelochemicals are available, major lacunae so far has been both laboratory bioassays and field procedures applied to establish the inhibitory or stimulatory effects of these allelochemicals in allelopathic processes. Laboratory bioassays are procedures that assess potency of a compound or a mixture of compounds (i. e. a plant leachate or root exudates) via its/their application-induced response on a receptor organism (Macías et al., 2000). The response of bioassays should be observed on physiological processes affected by an allelochemical. Nevertheless, most laboratory bioassays are based on plant responses. Bioassays properly designed can be more sensitive than chemical methods to detect bioactive substances. In most instances, response of germinating seeds or seedling growth to allelochemicals found in leachates/plant extracts are the first assays in allelopathic research. Controversy has arisen from ecological meaning of such laboratory assays, because they often have provided evidences of allelopathy not verifiable in the field suggesting that in most cases they can not explain processes occurring in natural conditions (Stowe, 1979). Despite these limitations, laboratory assays are undoubtedly important in allelopathic research. They allow analyzing how different factors (i. e. modes of allelochemical release, microbial activity, soil properties and special growth conditions) may affect the whole allelopathic process. The major problem with laboratory bioassays, however, is the absence of general accepted standard protocols and designs (Waller and Feng, 1995). In this chapter, general aspects of laboratory bioassays for allelopathy are provided including plant sampling, plant sample processing and assays for germination and seedling growth. We hope that criteria and procedures provided may help beginners to improve design of their laboratory assays in allelopathic studies.