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RESEARCH PRODUCT

Deciphering field-based evidences for crop allelopathy in weed regulation

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It is now essential to reduce the negative impacts of weed management and especiallyherbicide use. Weed-suppressive crop species/varieties hold promise for integrated andsustainable weed regulation. Competition for resources and allelopathy are the two mainunderlying mechanisms. Unlike competition, which is well studied and established, allelopathyby living crops remains a contentious mechanism. Although it is recognized that plants emit alarge number of substances, the effective role of these molecules is very challenging todemonstrate in the field. A major difficulty to dissociate the effects of allelopathy from thoseof competition for resources.Here we systematically and quantitatively review the literature, searching for field-basedevidence 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 agiven species, in order to help disentangling the effects of allelopathy from those ofcompetition. Our critical literature analysis also aims to identify weaknesses and strengths inmethodology, providing insights on optimal experimental designs and avenues for futureresearch.Our analysis shows that, in most articles, the role of crop competition is disregarded or notexhaustively studied. Consequently, contrary to authors’ conclusions, it cannot be determinedwhether weed regulation is due to allelopathy and/or competition. Overall, only 25 articlesstudied the differential effects of crop varieties on weed pressure in the field, explicitlyconsidering allelopathy and competition. Among them, 13 articles considered that bothallelopathy and competition explained varietal differences in weed regulation in the field, andfive articles identified allelopathy as the only explicative mechanism.In order to assess an effective role of allelopathy, we conducted a detailed analysis of these18 articles reporting an effect of allelopathy (alone or combined with competition). Wecombined a qualitative (relevance of experimental designs and protocols) and quantitativeapproach (range of variation of the measured variables, correlation analysis). Among thesearticles, only seven could provide convincing field-based evidence of allelopathy. The mostconvincing evidence was provided when combining several methods (field measurements onweeds and crop varieties and assessment of allelopathic potential in field or laboratory, linkedby a multiple regression), when results are consistent. However, although these seven articleswere convincing, we discussed some methodological weaknesses.129To further investigate allelopathy in the field we recommend to (i) finely characterize cropcompetition by measuring traits in the field, (ii) assess crop allelopathic potential withComplementary experiments in controlled conditions or by quantifying allelochemicals in thefield, and (iii) quantify the contribution of each studied trait/mechanism in explaining weedregulation in the field with multiple regression models. The consistent use of the suggestedguidelines, as well as alternative approaches (e.g. creation of varieties with alteredallelopathic compounds production, development of process-based simulation models) mayprovide a basis for quantifying the role of allelopathy in the field and, subsequently, fordesigning weed management strategies promoting weed biological regulation.Funding: INRAE, COPRAA project (which was supported by OFB as part of the Ecophyto calllaunched by the French Ministries in charge of Ecology, Agriculture, Health and Research) andPartnership Hubert Curien (PHC) – Germaine de StaëlReference:Mahé I, Chauvel B, Colbach N, Cordeau S, Gfeller A, Reiss A, Moreau D (in press) Decipheringfield-based evidences for crop allelopathy in weed regulation. A review.Agronomy for Sustainable Develop