Agronomy Journal
Volume 93 January–February 2001 Number 1
ALLELOPATHY SYMPOSIUM
Introduction
Maria Olofsdotter* and Azim U. Mallik
T
he papersin this special section were presented at a and-effect relationship between identifiable exudedsymposium, “Allelopathy in Natural and Managed chemical compounds and their effects on plants. Meth-Ecosystems,” of the Second World Congress on Allelo- odological concerns have been the major obstacle in the pathy, held at Lakehead University, Thunder Bay, Can- study of allelopathy. However, this is becoming easier ada, 9–13 Aug. 1999. The symposium aimed to provide to overcome with our increasing understanding of the a forum to present and discuss the latest results of allelo- chemical processes occurring in both natural and man-pathy research related to agriculture, forestry, and other aged ecosystems and with our ability to identify allelo-forms of vegetation management. A total of 44 oral chemicals. Progress in chemistry, biotechnology, and communications were presented in two sessions; of digital technology as well as an increased understanding these, 16 are presented in this issue. In addition to the of ecological processes help explain the rapid progress oral presentations in all of the sessions, 56 posters were in allelopathy research over the last four decades. presented on different aspects of allelopathy along with Breakthroughs in understanding the genetic control a CD-ROM demonstration on the history of allelopathy. of allelopathic interactions closely depend on research Two hundred scientists from 34 countries representing tools in molecular biology. Progress in this area can lead five continents attended the congress. The Second to the development of highly competitive plant varieties, World Congress on Allelopathy was organized under which might become a sustainable additional tool for the auspices of the International Allelopathy Society, weed management in agroecosystems. Similarly, digital and Lakehead University provided excellent confer- imaging techniques and information technology have ence facilities. the potential to play an increasingly important role in The history of allelopathy research is mired in specu- ecological studies and ecosystem-level studies of allelo-lation, faulty experimentation, and unreasonable con- pathy (e.g., succession studies in forests). They can also clusions. The discipline has gone through many ups and help in in-depth studies of structural changes at a cellular downs in generating interest among scientists in soil level caused by allelopathy. Having said that, we must science, agriculture, ecology, and forestry. However, also recognize that there is still a tendency to use inap-real progress in allelopathy began in the 1960s with the propriate, oversimplified methods such as plant extract work of Muller et al. (1964), and subsequently with the studies and the lettuce seedling bioassay in the quest to publication of the book Allelopathy by E.L. Rice in prove allelopathy. This creates a bad image of the sub-1974. Substantial progress has since been made in under- ject and provides fuel for most of its critics— standing allelopathy in an overall ecological perspective justifiably so.
as well as in how we can manipulate allelopathic interac- Traditionally, farmers have realized the benefits of tions to our advantage in agricultural practices (e.g., modifying the rhizosphere ecology of crops through weed control). crop rotation, mulching, burning, application of green It is difficult to demonstrate allelopathy in nature manure, etc. Allelopathy research today is trying to due to the complex interrelations between the different, unravel the mechanisms underlying the effects of these often genetically determined, characteristics of plant in- practices. The real benefits of allelopathic research can terference. Proving allelopathy also requires a cause- be realized only if our knowledge can be used to improve the sustainability of our production systems in agricul-M. Olofsdotter, IRRI, Philippines and Weed Sci., Royal Veterinary ture and forestry and the conservation of natural and and Agric. Univ., Denmark; and A.U. Mallik, Dep. of Biol., Lakehead seminatural vegetation. In this regard, we see progress Univ., Thunder Bay, Canada P7B 5E1. Received 30 Nov. 1999. *Corre- in allelopathy research on two fronts: one in applied sponding author (Mol@kvl.dk).
research on the cultural techniques of cropping systems, silviculture, and nature conservation and the second in Published in Agron. J. 93:1–2 (2001).
2 AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
crop improvement. To be effective, allelopathy research weeding. Allelopathy in smallholder fields is also dis-cussed in relation to sorghum [Sorghum bicolor (L.) must involve a range of scientists of many different
specializations with the overall objective of understand- Moerch] production. The mechanisms of weed-sup-pressive activity from turnip rape (Brassica rapa L.) ing the mechanisms of allelopathy. The future of
allelo-pathy research also lies in understanding the ecosystem mulch are discussed in a paper pointing out that isothio-cyanates might play an important role. Finally, the meth-perspective of the allelopathic phenomenon.
Demon-odology in allelopathy studies is highlighted and strating allelopathy and understanding its
intercon-discussed in a paper on the allelopathic effects of wheat nections with other ecological processes influencing
eco-(Triticum aestivumL.) straw on perennial ryegrass (
Lol-system functions will make a significant contribution to
ium perenneL.). the sustainable management of our natural resources.
The success of some weeds as weeds can also be The allelopathy papers in this issue of Agronomy
understood by understanding their allelopathic
charac-Journaltouch on all of the above mentioned facets of
teristics, and one paper attempts to reveal the effects allelopathy research. Five papers deal with the ability
of the noxious weedsCardaria drabaandSalvia syriaca
of allelopathic rice (Oryza sativaL.) to suppress weeds,
on vegetable crops in Jordan. starting with an overview of the progress made in using
Imbalances in any ecosystem might increase or reduce allelopathy in rice for weed control. A prerequisite for
the effects of allelopathic plants. Phytopathogenic mi-the use of allelopathy in rice is to be able to screen
croorganisms causing rust in ryegrass are given as an efficiently and to select breeding lines that are weed
example of enhancement of the allelopathic potential suppressive. High-performance liquid chromatography
against white clover (Trifolium repensL.). Microorgan-techniques have been developed that show promising
isms by themselves can also cause allelopathic effects, results in the correlation between the chemical content
and this is illustrated by two papers on the allelopathic of rice plants and their ability to suppress weeds under
effects of Aspargillus japonica and its allelochemical, laboratory conditions. These results are presented in
secaloic acid F. the second paper on rice allelopathy. The third paper
Most allelopathic plants are thought to exert their likewise deals with using rice extracts to screen rice lines
action through soil. Understanding soil chemistry and for weed-suppressing ability. To be able to evaluate the
soil processes is therefore of great importance in under-consequences of the widespread use of allelopathic rice
standing allelopathy. Therefore, a review paper is in-and to facilitate the understin-anding of the mechanisms
cluded in this issue on soil as a growth medium and an of rice allelopathy, it is important to identify the
allelo-active component of allelopathy through interaction, chemicals responsible for weed suppression. Different
decomposition, or chemical alterations of approaches can be taken to identify these
allelochemi-cals. Last but not least, two papers deal with examples cals, and the fourth paper on rice discusses
bioassay-of allelopathy and nutrient competition in forest eco-guided isolation as the method of choice for its ability
systems. to identify unknown chemicals. Finally, the last paper
Our final comment is an enormous thank you to all on rice reveals the identification of four quantitative
of the authors who have been most cooperative in the trait loci that are correlated with rice allelopathy. This
creation of this special section in the issue. A special paper proves for the first time that allelopathy is a
genet-thank you also goes to all the reviewers who reviewed ically driven phenomenon.
the manuscripts, an often time-consuming task with little Potential weed suppression from allelopathic field
reward. Thank you to all. crops is also discussed in several other papers. In
Mex-ico, a range of allelopathic legume cover crops has been REFERENCES
studied to understand the best management strategies
Muller, C.H., W.H. Muller, and B.L. Haines, 1964. Volatile growth for efficient weed suppression. One paper makes a spe- inhibitors produced by aromatic shrubs. Sciences (N.Y.) 143: cial effort to address the weed problems of resource- 471–473.
