Plant-Based Biostimulants and Plant Stress Responses

Abstract

Plants face a variety of biotic and abiotic stresses throughout their life cycle that adversely affect their growth and production. These stresses decrease the annual crop yield up to 70% globally and had created a problem of food shortage as well as the malnutrition for ever-increasing world population. Different strategies are being practiced to overcome these problems and found successful up to some extent. Exogenous use of plant growth promoters through different modes is one such among them that found helpful to improve the plant growth and production under stressful conditions and is being employed at commercial level to obtain better production. However, most of them are the inorganic chemicals and are found toxic for organism and are not environmental friendly. Trend is increasing toward the use of organic and environmental-friendly biostimulants with the ability to improve production and stress tolerance induction. Studies have revealed that exogenous use of these biochemicals through different modes (seed soaking, foliar spray, or as soil application) is found helpful in improving the plant growth and production under stressful conditions. These biostimulants include the chelation of macro- or micro-nutrients with different organic compounds, plant growth regulators of microbial origin, and plant-based biostimulants that are found helpful in improving the plant growth and production under stressful conditions. These include humic acids (humic and fulvic acid), chitosan, phosphites, bio-char, and plant-based extracts, including algal extracts and of different plant parts. These biostimulants along with the improvement of plant growth and production also found helpful to improve the yield and yield nutritional quality when applied exogenously through different modes. Improvements in the attribute due to the exogenous use of biostimulants under stressful condition are associated with their role in different physio-biochemical attributes, including plant antioxidative defense mechanism, plant photosynthetic efficiency, and plant water relation through the accumulation of different osmotica (osmolytes and osmoprotectants) that help to maintain cellular osmotic potential and better nutrient uptake and mobility. Plant-based biostimulants improve the plant growth due to the presence of different phytohormones and other secondary metabolites, vitamins, antioxidants, and the inorganic nutrients in the extract that directly affect the plant growth and production through improving the plant tolerance against abiotic stresses. Exogenous use of biostimulants through different modes also improves the plant growth, yield as well as the yield nutritional quality under stressful conditions. However, studies revealed that the effective dose for the induction of stress tolerance of these biostimulants is plant species, growth stage, and stress type specific. Moreover, the use of biostimulants for the effective improvement is also dependent on the mode of application. Although large work has been done to study the role of biostimulants in improving plant growth and production, still more is required for final recommendations. More attention is required in this regard and in future due to their non-toxic and environmental-friendly nature.