Allelopathy induces an underground dialogue : Study of the root exudates and volatile organic compounds of Secale cereale L. in interaction with Amaranthus retroflexus L.

Abstract

Allelopathy refers to the influence of an organism on the growth or development of another. This natural phenomenon mainly takes place in the soil by a biochemical mechanism called exudation. Rye (Secale cereale L.) is commonly known for its allelopathic potential and largely used as a cover crop. For that reason, it has been chosen as plant model for this study. On the other hand, pigweed (Amaranthus retroflexus L.) causes extent losses on crop yields, such as many other weeds encountered in all types of agroecosystems. First, the interaction between the two plants were investigated through complex culture system and neighborhoods. Biological observations show two very distinct trends of rye morphology towards the growing environment. Indeed, facing the experimental conditions, the aboveground features of rye remained relatively constant whereas the belowground characteristics largely varied. Secondly, the biological activity of rye raw extract was tested directly on pigweed. Even though germination and survival rate were globally not influenced, the biological essays gave a glimpse on how pigweed seeds and seedlings could react to rye presence in natural conditions. Thirdly, the allelochemical content of rye root exudates was analyzed. Two benzoxazinoids are mostly known to take part in poaceous allelopathy: DIMBOA and DIBOA. Manifestly, only DIBOA was revealed in rye’s exudates, regardless of the plant present next to it during its growth. Lastly, the VOCs emission of rye root was also studied. A specific experimental device allowed the extraction of VOCs directly from the rye rhizosphere. Several biogenic compounds were detected but very few of them are already listed for presumed allelopathic activities. This aspect of this work opens the door towards a whole new field in the study of volatile plant metabolites. To conclude, viewing the actual environmental context, more sustainable agronomic practices are urgently required. Allelopathy might be one the key for better weed management as long as plant interactions with their surrounding are well understood. This work contributes to a better comprehension of the war that is taking place underground.