Allelopathy and allelochemicals from microalgae: An innovative source for bio-herbicidal compounds and biocontrol research

The intensive use of synthetic herbicides over the past 50years has led to a number of deleterous impacts on the terrestrial and aquatic environment and is a serious challenge to the ability to sustain agricultural production into the future. In order to remedy this problem, the use of biocontrols is rapidly accelerating and initiating the transition of the agricultural system into an agroecological system. Microalgae (in its wider sense, eukaryote and cyanobacteria) from marine and freshwater habitats are known to produce a diverse range of toxic or otherwise bioactive allelochemical metabolites for growth, communication and defense. Between the search for innovative active molecules and the development of new production processes at the dawn of biotechnology, microalgae have an immense potential in their contribution to biocontrol products. Microalgal organisms can be grown in mass cultures enabelling their manipulation for optimal production of bioactive substances, giving them a significant advantage over terrestrial plants in exploring their effectiveness. In this review we will present the structural diversity of allelochemical compounds and their role for microalgae, the competitive advantages that these compounds provide to microalgae compared to competing species, as well as their potential as biological control agents and bioherbicides.