Unravelling the bioherbicide potential of Eucalyptus globulus Labill: Biochemistry and effects of its aqueous extract

Abstract

In the worldwide search for new strategies in sustainable weed management, the use of plant species able to produce and release phytotoxic compounds into the environment could be an effective alternative to synthetic herbicides. Eucalyptus globulus Labill. is known to be a source of biologically active compounds responsible for its phytotoxic and allelopathic properties. Our previous results demonstrated the bioherbicide potential of eucalyptus leaves incorporated into the soil as a green manure, probably through the release of phytotoxins into the soil solution. Thus, the aims of this study were to understand the phytotoxicity of the eucalyptus leaves aqueous extract applied in pre- and post-emergence, and to identify and quantify its potentially phytotoxic water-soluble compounds. The effects were tested on the germination and early growth of the model target species Lactuca sativa and Agrostis stolonifera, and on physiological parameters of L. sativa adult plants after watering or spraying application. Dose-response curves and ED50 and ED80 values for eucalyptus aqueous extracts revealed pre-emergence inhibitory effects on both target species, effects being comparable to the herbicide metolachlor. While spraying treatment reduced the aerial and root biomass and increased the dry weight/fresh weight ratio of lettuce adult plants, watering application reduced protein contents and chlorophyll concentrations with respect to control, reflecting different modes of action depending on the site of phytotoxin entry. Via HPLC analyses, a total of 8 phenolic compounds (chlorogenic, two ρ-coumaric derivatives, ellagic, hyperoside, rutin, quercitrin, and kaempferol 3-O-glucoside) and other 5 low weight organic acids (citric, malic, shikimic, succinic and fumaric acids) were obtained from aqueous extract, the latter being identified for the first time in E. globulus. Despite some phytotoxic effects were found on lettuce adult plants, the use of eucalyptus aqueous extract would be discarded in post-emergence, whereas it was promising as a pre-emergence bioherbicide.

Activity of Ailanthus altissima (Mill.) Swingle Extract as a Potential Bioherbicide for Sustainable Weed Management in Horticulture

“…Weeds reduce crop yield by competing for nutrients, light, and moisture [1]. Sustainable weed management is one of the main challenges for both conventional and organic horticulture [2]. Current weed control in horticultural production includes synthetic herbicides and physical methods [3].…”

Allelopathic properties of Calliandra haematocephala Hassk. extracts and fractions as an alternative for weed management in quinoa and rice crops

“…Chemical compounds extracted from many plant species have shown allelopathic properties, which give a great hope in the development of non-synthetic alternatives for weed control. Most studies have found allelochemicals mainly in aqueous extracts (Chon et al 2003;Tsao et al 2002;Xuan et al 2005;Hill et al 2007;Reigosa and Pazos-Malvido 2007;Shrestha 2009;Lin et al 2010;Zhang et al 2010;Rueda-Ayala et al 2015;Amari et al 2014;Puig et al 2018), describing almost exclusively inhibitory effects towards germination and root elongation. The aqueous extracts of C. haematocephala used in this study evidenced a high content of chemical compounds that inhibited the development of target species more than ethanol based extracts.…”

“…4) than aqueous extracts. Aqueous extracts have shown a joint action of several contained compounds at once (Puig et al 2018).…”

“…Less than 10% of available biopesticides are bioherbicides, while weeds are still the major cause of yield loss in current agriculture (Charudattan 2001). Promising inhibitory effects on seed emergence have been observed from essential oil extracts of eucalyptus (Zhang et al 2010;Puig et al 2018) or Black walnut (Shrestha 2009), the latter being already commercially formulated as a bioherbicide that limits completely the growth of Conyza canadensis at a concentration of 33%. The flower extracts identified and tested in this study already fulfill some requirements to be acceptable and efficient biopesticides, such as weed specificity, minimal effect on crops, easy and cheap elaboration.…”

“…Allelopathic effects may be attributed to phenolic compounds found in one or various plant parts, and these effects can be strengthen by mixing compounds of different plant species (Reigosa and Pazos-Malvido 2007). Puig et al (2018) identified allelopathic activity and the chemical composition of different species of the genus Eucalyptus (Myrtaceae). Phytotoxic effects of E. globulus aqueous extracts affected the germination and radicle elongation of some crops and weeds with specific modes of action on different target species.…”