In this study, we investigated in vitro the potential of Trichoderma harzianum to produce bioactive secondary metabolites that can be used as alternatives to synthetic compounds. The study focused on analyzing two extracts of T. harzianum using ethyl acetate and n-butanol solvents with different polarities. The extracts were examined using phytochemical analysis to determine the content of polyphenols, flavonoids, tannins, and alkaloids. Thin-layer chromatography (TLC) and Gas chromatography-mass spectroscopy (GC-MS) analysis were used to profile volatile organic metabolites (VOCs) present in the extracts. Furthermore, the extracts were tested for their antifungal ability using the poison food technique. For measuring antioxidant activity, the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) test was used. Trichoderma harzianum was shown to have a significantly high content of tannins and alkaloids, with a noticeable difference between the two extracts. GC-MS analysis identified 33 potential compounds with numerous benefits that could be used in agriculture and the medicinal industry. Moreover, strong antifungal activity was identified against Sclerotinia sclerotiorum by 94.44%, Alternaria sp. by 77.04%, and Fusarium solani by 51.48; similarly, the IC₅₀ of antioxidant activity was estimated for ethyl acetate extract by 71.47% and n-butanol extract by 56.01%. This leads to the conclusion that Trichoderma harzianum VOCs play a significant role as an antifungal and antioxidant agent when taking into account the advantageous bioactive chemicals noted in the extracts. However, to our knowledge, this is the first study in Algeria presenting detailed phytochemical analysis and GC-MS profiling of Trichoderma harzianum for two extracts, ethyl acetate and n-butanol.

The increasing concerns over climate changes and environmental impacts of synthetic agrochemicals have led to a growing interest in natural alternatives such as seaweed-based biostimulants. These extracts contain diverse bioactive compounds, including phytohormones, polysaccharides, proteins, polyphenols, and vitamins, which contribute to enhanced plant growth, stress tolerance, and soil health. Seaweed biostimulants have demonstrated their ability to improve germination, growth, and yield under both optimal and stressful conditions. Additionally, seaweed-derived compounds influence microbial communities, promoting beneficial interactions that enhance soil structure and fertility. Their different mode of applications further expands their utility in modern agriculture. Despite their numerous advantages, challenges remain regarding cultivation, large-scale production, and regulatory frameworks. Further research is needed to optimize extraction methods, elucidate mechanisms of action, and explore economic feasibility. This systematic review brings focus to the potential of seaweed-based biostimulants as sustainable agricultural inputs, discussing their chemical composition, mechanisms of action, techniques of extraction, application strategies, challenges and future perspectives for improving crop productivity and resilience.