Control of soil-borne plant pests using glucosinolate-containing plants

Weeds are known to cause enormous losses due to their interference in agroecosystems. Because of environmental and human health concerns, worldwide efforts are being made to reduce the heavy reliance on synthetic herbicides that are used to control weeds. In this regard the phenomenon of allelopathy, which is expressed through the release of chemicals by a plant, has been suggested to be one of the possible alternatives for achieving sustainable weed management. The use of allelopathy for controlling weeds could be either through directly utilizing natural allelopathic interactions, particularly of crop plants, or by using allelochemicals as natural herbicides. In the former case, a number of crop plants with allelopathic potential can be used as cover, smother, and green manure crops for managing weeds by making desired manipulations in the cultural practices and cropping patterns. These can be suitably rotated or intercropped with main crops to manage the target weeds (including parasitic ones) selectively. Even the crop mulch/residues can also give desirable benefits. Not only the terrestrial weeds, even allelopathy can be suitably manipulated for the management of aquatic weeds. The allelochemicals present in the higher plants as well as in the microbes can be directly used for weed management on the pattern of herbicides. Their bioefficacy can be enhanced by structural changes or the synthesis of chemical analogues based on them. Further, in order to enhance the potential of allelopathic crops, several improvements can be made with the use of biotechnology or genomics and proteomics. In this context either the production of allelochemicals can be enhanced or the transgenics with foreign genes encoding for a particular weed-suppressing allelochemical could be produced. In the former, both conventional breeding and molecular genetical techniques are useful. However, with conventional breeding being slow and difficult, more emphasis is laid on the use of modern techniques such as molecular markers and the selection aided by them. Although the progress in this regard is slow, nevertheless some promising results are coming and more are expected in future. This review attempts to discuss all these aspects of allelopathy for the sustainable management of weeds.

Allelopathic Interactions and Allelochemicals: New Possibilities for Sustainable Weed Management

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.

Allelopathy--a natural alternative for weed control.

Glucosinolates in crop plants

Summary Spatially segregated root systems have been documented among conspecifics and among species at the scale of whole root systems and individual fine roots. Root segregation is often caused by architectural constraints, proliferation in particular microsites and plastic responses to competition for resources, but there is also evidence to suggest that allelopathy and non-toxic signals contribute to active root segregation. Root segregation appears to provide competitive advantages for water and nutrients for some species, as well as advantages of space itself. Plant growth and photosynthesis decreases when space is physically restricted, even when other resources are abundant. Moreover, plants appear to be able to compete for space independently of nutrient, water or light resources. Species that utilise resources efficiently and conservatively may particularly benefit from active root segregation because more profligate neighbouring species would not be able to take resources that were being utilised slowly. Stressful conditions, produced by adverse physical conditions and herbivory, have been shown to enhance the production of secondary metabolites and increase root exudation, mechanisms that can affect spatial root segregation. Resource availability may also determine the relative importance of root segregation in plant communities. A large portion of the evidence for root segregation comes from arid and semi-arid environments, where resources are often low. In resource-rich communities the defence of space may be less important. For animals, the defence and exclusive use of space is considered to be evidence for territoriality and suggests that organisms that exhibit such behaviour are avoiding the costs and uncertainties of “scramble” competition. Active root segregation and the defence of space by plants indicates that plants also may be territorial and opens the possibility of a level of taxonomic generality in population biology that is not currently recognised.

Spatial root segregation : Are plants territorial?

Exposure of germinating seeds of lettuce, barnyard grass and wheat to volatile substances released from pulverised leaves of some Cruciferae species resulted in delay of germination and reduction of overall growth.B. juncea andB. nigra volatiles were the most damaging to all of the tested species. It is suggested that degradation products of glucosinolates occuring in cruciferous plants caused this allelopathic action.

W. Oleszek

Papers

Allelopathic effects of volatiles from some Cruciferae species on lettuce, barnyard grass and wheat growth