Deciphering field-based evidences for crop allelopathy in weed regulation
Résumé
It is now essential to reduce the negative impacts of weed management and especially
herbicide use. Weed-suppressive crop species/varieties hold promise for integrated and
sustainable weed regulation. Competition for resources and allelopathy are the two main
underlying mechanisms. Unlike competition, which is well studied and established, allelopathy
by living crops remains a contentious mechanism. Although it is recognized that plants emit a
large number of substances, the effective role of these molecules is very challenging to
demonstrate in the field. A major difficulty to dissociate the effects of allelopathy from those
of competition for resources.
Here we systematically and quantitatively review the literature, searching for field-based
evidence of the role of allelopathy (by root exudation of living crops) in weed regulation,
independently of competition. A focus is made on studies comparing different varieties of a
given species, in order to help disentangling the effects of allelopathy from those of
competition. Our critical literature analysis also aims to identify weaknesses and strengths in
methodology, providing insights on optimal experimental designs and avenues for future
research.
Our analysis shows that, in most articles, the role of crop competition is disregarded or not
exhaustively studied. Consequently, contrary to authors’ conclusions, it cannot be determined
whether weed regulation is due to allelopathy and/or competition. Overall, only 25 articles
studied the differential effects of crop varieties on weed pressure in the field, explicitly
considering allelopathy and competition. Among them, 13 articles considered that both
allelopathy and competition explained varietal differences in weed regulation in the field, and
five articles identified allelopathy as the only explicative mechanism.
In order to assess an effective role of allelopathy, we conducted a detailed analysis of these
18 articles reporting an effect of allelopathy (alone or combined with competition). We
combined a qualitative (relevance of experimental designs and protocols) and quantitative
approach (range of variation of the measured variables, correlation analysis). Among these
articles, only seven could provide convincing field-based evidence of allelopathy. The most
convincing evidence was provided when combining several methods (field measurements on
weeds and crop varieties and assessment of allelopathic potential in field or laboratory, linked
by a multiple regression), when results are consistent. However, although these seven articles
were convincing, we discussed some methodological weaknesses.129
To further investigate allelopathy in the field we recommend to (i) finely characterize crop
competition by measuring traits in the field, (ii) assess crop allelopathic potential with
Complementary experiments in controlled conditions or by quantifying allelochemicals in the
field, and (iii) quantify the contribution of each studied trait/mechanism in explaining weed
regulation in the field with multiple regression models. The consistent use of the suggested
guidelines, as well as alternative approaches (e.g. creation of varieties with altered
allelopathic compounds production, development of process-based simulation models) may
provide a basis for quantifying the role of allelopathy in the field and, subsequently, for
designing weed management strategies promoting weed biological regulation.
Funding: INRAE, COPRAA project (which was supported by OFB as part of the Ecophyto call
launched by the French Ministries in charge of Ecology, Agriculture, Health and Research) and
Partnership Hubert Curien (PHC) – Germaine de Staël
Reference:
Mahé I, Chauvel B, Colbach N, Cordeau S, Gfeller A, Reiss A, Moreau D (in press) Deciphering
field-based evidences for crop allelopathy in weed regulation. A review.
Agronomy for Sustainable Develop