Contribution on the study of allelopathic interactions between Amaranthus retroflexus L. and Secale cereale L.

Abstract

Amaranthus retroflexus L., commonly known as redroot pigweed, is a well-known summer weed that poses significant challenges to multiple cropping ecosystems. Historically, intensive use of herbicides has been the primary method of weed control since the Green Revolution. However, this approach is becoming less effective due to the increasing adaptation and resistance of weed species to herbicides. Additionally, the negative side effects associated with herbicide use emphasize the need for the implementation of sustainable weed management practices. Considering the above considerations, the adoption of rye (Secale cereale L.), which is one of the most potent allelopathic crops, holds significant importance. The problem addressed in this study is the lack of knowledge concerning the causes and effects of the interactions between those two plant species. The focal plant in this case was rye. Two populations were grown in controlled conditions and in hydroponics. One group serving as a control, and the other group being subjected to an aqueous extract of redroot pigweed. Different potential effects of this extract were monitored during 9-day long development of the rye seedlings. Below ground interaction between the focal plant and other organisms is suspected to be strongly modulated by volatile organic compounds (VOCs). To elucidate this mystery, the volatilome inside the hydroponic system was determined using a custom-made growth apparatus that would allow the direct pumping of root volatiles using dynamic headspace sampling and followed by GC-MS analysis of the captured compounds. The investigation of phenotypical variables in the study included gravimetric analysis of biomass allocation and root scanning to assess root architecture. These variables served as indicators of potential inhibition, stimulation, or alteration of rye's developmental pattern. Lastly, rye is specialized in the production of allelochemicals called benzoxazinoids. Their production, accumulation and release are strongly dependent on environmental stimuli. The inducible production of the root treatment using metabolites belonging to redroot pigweed was investigated. Results of the present experimentations show that the aqueous extract of redroot pigweed is affecting the growth pattern of rye roots. The promotion of lateral root elongation was already observed after six days of treatment. Perturbation of the auxin-ethylene growth regulation system is suspected. The overall allocation of biomass from root to shoot does not show significant variations when comparing the two populations. Regarding the analysis of the volatilome, potential constitutive signals were identified in rye roots, both in control and treated groups. Furthermore, treatment appeared to stimulate the emission of certain volatile organic compounds (VOCs) while suppressing others. Some of the detected VOCs were attributed to emission by plant growth-promoting rhizobacteria rather than the roots themselves. Additionally, some of these compounds have been found to possess toxic activity, thereby inhibiting potential pathogenic organisms within the rhizosphere. This underscores the fact that rye employs not only benzoxazinoids or exudates, but also VOCs, to mediate subterranean interactions. 3 In the context of treatment with an extract, no discernible variation in the benzoxazinoid content of rye shoot was detected. Despite its susceptibility to external stimuli, the priming of the defense mechanisms of rye shoots were not observed.