Significant progress has been achieved in the use of biostimulants in sustainable agricultural practices. These new products can improve plant growth, nutrient uptake, crop yield and quality, stress adaptation and soil fertility, while reducing agriculture’s environmental footprint. Although it is an emerging market, the biostimulant sector is very promising, hence the increasing attention of the scientific community and agro-industry stakeholders in finding new sources of plant biostimulants. Recently, pro- and eucaryotic microalgae have gained prominence and can be exploited as biostimulants due to their ability to produce high-value-added metabolites. Several works revealed the potential of microalgae- and cyanobacteria-based biostimulants (MCBs) as plant growth promoters and stress alleviators, as well as encouraging results pointing out that their use can address current and future agricultural challenges. In contrast to macroalgae biostimulants, the targeted applications of MBs in agriculture are still in their earlier stages and their commercial implementation is constrained by the lack of research and cost of production. The purpose of this paper is to provide a comprehensive overview on the use of this promising new category of plant biostimulants in agriculture and to highlight the current knowledge on their application prospects. Based on the prevailing state of the art, we aimed to roadmap MCB formulations from microalgae and cyanobacteria strain selection, algal biomass production, extraction techniques and application type to product commercialization and farmer and consumer acceptance. Moreover, we provide examples of successful trials demonstrating the beneficial applications of microalgal biostimulants as well as point out bottlenecks and constraints regarding their successful commercialization and input in sustainable agricultural practices.

Cyanobacteria are well known for their biofertilizing capacities, which can enhance soil fertility and plant growth. This study aims to evaluate the biofertilizing effects of the indigenous nitrogen-fixing soil cyanobacterium Anabaena cylindrica on the growth, biochemical, and physiological responses of wheat, as well as soil fertility. Medium filtrate, aqueous extract, sonicated culture, and crude culture of A. cylindrica at different doses (50%, 25%, 1%, and 0.2% v/v) were applied using a soil drench under greenhouse conditions. After 40 days of growth, all cyanobacterial suspensions significantly increased wheat growth, biochemical properties, and plant mineral composition compared to the controls. The greatest improvements were observed with the application of cyanobacterial suspensions at the highest concentrations, 25% and 50%. These doses also significantly enhanced the nutritional and physicochemical properties of the soil. Among the different treatments, soil inoculation with crude culture (living cells) and growth medium filtrate at 50% were the most efficient. The wheat growth–promoting effect was attributed to the intracellular or released bioactive compounds of A. cylindrica, such as polysaccharides, proteins, indole acetic acid phytohormone, nitrogen, phosphorus, and potassium. This study demonstrates that terrestrial A. cylindrica-derived suspensions promote wheat growth and can be used as an effective and eco-friendly biofertilizer to enhance plant growth and crop productivity.

Cyanobacteria-based bioinoculants represent a sustainable solution for enhancing soil fertility and crop productivity. This research assessed the biofertilizing potential of two indigenous nitrogen-fixing cyanobacteria strains (Nostoc punctiforme Har. and Anabaena cylindrica Lemmerm.) on tomato growth and yield. A greenhouse experiment was conducted to study their effects on soil properties, plant growth and physiology, and fruit yield/quality. The strains were applied individually, as a consortium, or combined with organic or mineral fertilizers at half the standard dose (50%). All bioinoculants improved soil fertility, plant growth, and fruit yield/quality compared to the control. The most significant improvement was observed in the consortium amended with 50% of conventional fertilizer (compost or NPK), compared with individual strains. Correlation analysis revealed strong positive associations between photosynthetic pigments, plant productivity, and fruit biochemical traits, indicating coordinated physiological responses under the applied treatments. The results demonstrated that the consortium of diazotrophic terrestrial cyanobacteria possesses tomato biofertilizer properties that can be efficiently used in crop production. These findings suggest that such formulations offer a cost-effective approach to tomato cultivation and present a sustainable alternative for integrated and optimized fertilizer management.

The use of biostimulants has emerged as a promising strategy for enhancing seed vigor, germination, and seedling growth. This is due to the composition of beneficial substances considered as biostimulants that modulate plant physiology and metabolism. In this context, the interest in biostimulants is growing and the use of microalgal extracts is becoming more widespread. This study aims to assess the effect of Chlorococcum sp. aqueous extracts on the germination indices and the biometric and biochemical parameters of sesame (Sesamum indicum L.). Chlorococcum sp. culture exhibited favorable growth characteristics, including high productivity, specific growth rate, and short generation time. Furthermore, analysis of the extract demonstrated that it contains a high concentration of biomolecules, which suggests significant biostimulant potential. Importantly, the results also showed a significant improvement in germination indices as well as in biochemical parameters and photosynthetic pigments in seeds treated with the highest extract concentration (2 g/L). Furthermore, improvement in biometric parameters, including radicle length as well as fresh and dry weight, was observed at low extract concentration (0.1 and 0.5 g/L). Additionally, no phytoinhibitory effects were detected. Overall, the application of microalgal aqueous extract highlights a strong potential as a sustainable and cost-effective alternative to conventional synthetic chemical fertilizers, thereby promoting the development of an environmentally friendly agricultural practice of sesame cultivation.

Microalgae-based biostimulants are gaining increasing interest worldwide for promoting sustainable agriculture. The environmental risks associated with synthetic agrochemicals can be mitigated by using microalgae to enhance crop yield and quality. Cumin (Cuminum cyminum L.) is an herbaceous plant and ranks among the most popular seed spices worldwide. It is characterized by a low germination rate and poor seedling establishment, which negatively impact overall crop yield. To address these challenges, the present study investigates the potential of Chlorococcum sp. aqueous extract as a sustainable and cost-effective solution to overcome cumin seed dormancy and enhance germination. Results showed that Chlorococcum sp. exhibits a notably rapid growth rate (0.45 day⁻¹) and high biomass productivity (1.51 g/L/day). Additionally, the biochemical composition of the extract revealed a high concentration of bioactive compounds, including polyphenols (63.46%), flavonoids (29.36%), and Indole-3-acetic acid (5.38%), which make it an eco-friendly biostimulant for agricultural applications. Regarding germination, a single seed treatment with doses of 0.5 g/L and 1 g/L was efficient in achieving final germination percentages of 100% and 96.66%, respectively, and significantly increased the seedling vigor index and photosynthetic pigment content. Furthermore, these concentrations stimulated the synthesis and accumulation of key primary metabolites, including proteins and polysaccharides, while increasing phenolic and flavonoid levels compared to the control, suggesting enhanced growth and improved antioxidant defenses against environmental stressors. Overall, these findings highlight that Chlorococcum sp. aqueous extract serves as an innovative biological approach to overcoming cumin seed dormancy and enhancing germination, offering an alternative and sustainable solution to conventional synthetic fertilizers.