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Response of canola to foliar application of moringa (Moringa oleifera L.) and brassica (Brassica napus L.) water extracts

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Sustainable crop production under changing climate is crucial to feed the increasing population of the world. Efforts are underway to discover novel strategies to ensure global food security. Allelopathy is one such phenomenon that can help in this regard. It is a direct or indirect and positive or negative effect of plant species on other plant species and microorganisms, through the release of secondary metabolites known as allelochemicals. Brassica species are well known for their allelopathic potential as most of them endogenously produce potent allelochemicals such as glucosinolates, allyl isothiocyanates, and brassinosteroids. These allelochemicals are highly phytotoxic to target species when released at high concentrations and, therefore, affect their growth and development. This review illustrates the potential role of Brassica allelopathy for crop production in modern agriculture. Allelopathic potential of Brassica species can be utilized for weed management by using them as cover crops, companion crops, and intercrops, for mulching and residue incorporation, or simply by including them in crop rotations. Similarly, the expression of allelochemicals from these species have great value in the management of crop pests and diseases, and abiotic stresses. Most of these allelochemicals can also act as crop growth promoters when released or applied at low concentrations. Although the use of chemical herbicides, pesticides, and synthetic growth regulators is currently inevitable for crop production, the use of ecological options like allelopathy may help in achieving global food security sustainably. Exploring the potential of Brassica allelopathy could be promising in achieving higher productivity without compromising the environmental safety.
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Allelopathy has been explored recently as a substitute for chemicalherbicides to reduce environmental pollution. Various plant water extractsalone and in combinations with each other may exert their influence differentlyon weeds and crop plants. Response of wheat and its weeds to foliarapplication of sorghum (Sorghum bicolor), sunflower (Helianthus annuus) andeucalyptus (Eucalyptus camaldulensis) water extracts individually and incombinations with each other at different doses were tested under fieldconditions. Concentrated sunflower water extract at the rate of 12 L ha-1sprayed at 30 and 40 days after sowing gave consistently better weed controland increased wheat yield by 5.5% over control. A combination of waterextracts of sorghum, sunflower and eucalyptus each at the rate of 12 L ha-1and 8 L ha-1 were also economical. However, conventional methods like handweeding and herbicides, though effective in weed control, were uneconomicaldue to higher costs.
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The study was performed to examine interactions in seed germination in a mixture of leguminous crops and grasses. In red clover (Trifolium pratense), lucerne (Medicago saliva), birdsfoot trefoil (Lotus corniculatus) seeds grown in association with tall fescue (Festuca arundinacea) germination percentage was evaluated on days one to seven. The experiments involved two treatments of seed geometry and two treatments of seed density. The species grown in monoculture served as control. The effect of released allelopathic substances was most marked in a combination of birdsfoot trefoil and grass resulting in reduced germination percentage of both seeds at the start of culture. The allelopathic effects of substances released from seeds acted inhibitory or stimulating in the first days of germination. To the end of evaluation there were no significant differences in germination percentage among seed mixtures and the controls. Sowing density and seed geometry had no unambiguous and significant effect on germination percentage. Of the leguminous crops studied birdsfoot trefoil exhibited the highest allelopathic potential and also tall fescue was considered as a grass with a high allelopathic potential. The results are in good agreement with the concentrations of phenolic substances given in a follow-up to this study.
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To show that the modes of brassinolide (BR) action in the control of seedling growth are unique and different from those of auxin (IAA) and gibberellin (GA4), experimental results obtained with hypocotyls of light-grown cucumber seedlings are described The stimulating effect of BR on the elongation of hypocotyl sections is characteristic in terms of its very low effective concentration range, pH independence, the modes of interactions with other hormones, the effects of inhibitors, etc. The most interesting action of BR is to reinforce seedlings against cold stress.