Products of allelopathic plants for organic weed management: Environmentally approach

Allelopathic substances from different crops may have synergistic effects and can be applied in the mixture. In the previous research, several crop plants have been identified as phytotoxic against various weeds like sorghum, brassica, and sunflower. However, the effect of their tank mixture with each other was never studied in cotton before. Furthermore, it was not sure before this study whether the allele chemicals present in these crops viz. sorghum, sunflower and brassica can have synergistic or additive effects when applied in combination. Herbicides account for 42% of global pesticides’ use. Therefore, recent emphases have been on biological weed control measures so as to reduce dependence on synthetic herbicides and finding alternative strategies for weed control in agro ecosystems. Allelopathy is one of such strategies that can be explored for biological weed control of cropping systems. The mimosine that occurs in Leucaena has the potential to be used as a bio-herbicide in weed management. Mimosine is the main allelochemicals in Leucaena and is responsible for the strong allelopathic activity of the plant. The allelopathic effects of L. leucocephala towards several agricultural crops and forest trees have been reported.
Plant seedlings of various crops possess allelopathic potential or weed-suppressing activity, including cucumber (Cucumber sativa L.), oat (Avena spp.) and rice (Oryza sativa L.). The main barley allelochemicals are the alkaloids gramine and hordenine which play a significant role in barley allelopathic potential and its defense against weeds, insects, or pathogens. In particular, barley allelopathic extracts have the ability to reduce emergence and growth of serious weeds like winter wild oat (Avena sterilis L.), hood canary grass (Phalaris paradoxa L.), black grass (Alopecurus myosuroides Huds.), great brome (Bromus diandrus Roth.), and wild mustard (Sinapis arvensis L.). This growth reduction has been mainly attributed to lipid peroxidation. Tamarindus contains allelochemicals on roots, leaves, seeds and bark , however, its allelopathic potential has not yet been compared to that of other allelopathic species such as Parthenium. Citharexylum (Citharexylum spinosum L) is equally a tree, a tropical plant with numerous usages but also know to have some allelopathic potential. Flower extracts have proved to be extremely potent to lettuce seed germination and seedlings growth and are very little known regarding its leaves phytotoxity. Consequently, the current experiment will provide additional information regarding Citharexylum leave allelopathic potential.
Sunflower (Helianthus annuus L.). In Asteraceae members including sunflower, the main allelochemicals are sesquiterpenes, especially heliannuoles, sesquiterpene lactones and bisnorse squiterpenes, in addition to triterpenes and flavonoids Its allelopathic effects have been tested on both other crops and weeds, in field conditions and in vitro bioassays. In recent years, the allelopathic potential of Cynara cardunculus L., an herbaceous perennial species belonging to the Mediterranean basin, was assessed on seed germination and seedling growth of some weeds and target crops. Allelochemicals responsible for C. cardunculus allelopathy are the sesquiterpene lactones cynaropicrin, deacylcynaropicrin, 11, 13-dihydro-deacylcynaropicrin, aguerin B, grosheimin, 11,13-dihydroxy-8-deoxygrosheimin and cy-naratriol, as well as polyphenols such as caffeoylquinic and dicaffeoylquinic acids, luteolin and apigenin derivatives. Around 800 species of plants produce biologically active substances, but only a few of them are used in agricultural practice. However, in recent years, there has been an increase in interest in allelopathy due to the effective use of allelochemicals in plant protection, such as bioherbicides, bio insecticides, biofungicides and growth regulators.