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Biostimulant: It is in the genes A rapidly growing human population and the longevity afforded by new medical technologies mean that the world’s need for food, fibre and feed is expanding at a rapid pace. It is estimated that an increase of almost 100% in agricultural production will be needed to sustain the human population in 2050 (Elferink & Schierhorn, 2016). JOHAN JANSE VAN RENSBURG1 IDA WILSON2 1 2
ORO AGRI BIOREVOLUTION
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gricultural productivity is challenged by climate change and notably by climate change-driven water scarcity. This is evident by wide scale global drought which is currently being experienced in many important agricultural areas around the world. Rising and fluctuating temperatures, erratic and unpredictable rainfall patterns and extreme weather impacts crop yields (Challinor et al., 2014), while soils are degraded and become saline due to water scarcity. It is estimated that 50% of arable land will be affected to some extent by salinity (Bartels & Sunkar, 2005). Biostimulants are products known to increase plant growth and resistance to biotic and abiotic stresses. In general, these products favour the performance of the plant’s natural processes and reduce the need for the application of fertilisers. Biostimulants are known to increase yields and quality of crops, mainly by enhanced effects on the uptake of nutrients by plants. Various substances are used in biostimulant products, including humic acids, algae extracts and plant growth-promoting bacteria (De Vasconcelos & Chaves, 2019). In a study conducted at Stellenbosch University, the effects of the biostimulant Crop4Life (C4L), a commercially available biostimulant, was evaluated on a molecular level for the changes that it induced in the model plant Arabidopsis thaliana when watered with normal water or saline water. The effects of C4L on biomass, chlorophyll, stress response metabolites and stomatal conductivity was assessed. The study provided evidence that C4L mitigated salt stress in the plants evaluated (Fig. 1). Chlorophyll content and biomass increased and metabolites induced under stress conditions were altered. Additionally, the stomatal conductance was reduced, which points to better water use efficiency by the saltstressed plants. It is possible that this stress mitigation is not only restricted to salt stress. According to Zhu (2016), many of the genes activated by salt stress, also responds to cold or drought stress, thus raising the possibility that C4L may be a valuable stress alleviating treatment in crop production systems experiencing other kinds of stress, although this needs to be confirmed with
GROENTE & VRUGTE | JULIE • AUGUSTUS 2021
Figure 1: Above-ground biomass production of Arabidopsis thaliana in a salt-stressed environment, when plants treated with (a) saline water, and (b) saline water after receiving a soil drench of Crop4life.
follow up studies. It is known that C4L elicits physiological responses in plants which increase crop yield and quality. The study by Loubser also evaluated the plant’s responses to the biostimulant on the molecular level (via RNA sequencing). Crop4Life, applied as a soil drench at 0,01% (v/v) stimulated above-ground biomass and altered genes across several biochemical pathways. The transcriptome of an organism gives information on the molecules that are synthesized, and the underlying genes involved. Transcriptomics evaluates the transcriptome – it asks how the genes are expressed, and how resultant metabolites are influenced. When the transcriptomic profile of C4L-treated-plants was compared to those that did not receive C4L, 8% of genes were expressed differently from control plants. Approximately 5% of genes were up-regulated. Up-regulation means that more of a specific protein will be produced by a gene, and about 3% of genes were down-regulated, meaning that the expression of a protein is decreased. Notably, genes involved in photosynthesis, cell wall formation, carbohydrate metabolism, secondary metabolism and signalling were up-regulated, which possibly explains increases in plant growth. The study also evaluated the responses of tomato (Solanum lycopersicum) plants on the molecular level (again with RNA sequencing). The reaction of plants to which a foliar spray of C4L was applied at a concentration of 0,05% (v/v) was evaluTO PAGE 16
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