Isolation and selection of microalgae capable of stimulating rice plant development and seed production

The growing global demand for food, in addition to the environmental impacts of agricultural intensification and climate change, reinforce the need for sustainable alternatives to maintain and increase agricultural productivity. Microalgae are widely available renewable resources for application in agricultural environments. There is a vast biodiversity of microalgae species, and their versatile metabolism produces a great diversity of compounds that favor the capture and supply of nutrients, improve soil characteristics, and stimulate plant growth. In this study, we evaluated the production of indole compounds, exopolysaccharides, siderophores, and the development capacity of microalgae strains of the genera Chlamydomonas sp., Chlorella sp. and Desmodesmus sp. isolated from different Brazilian States. Microalgae that produced a greater range of compounds and developed more quickly were selected for the production of aqueous extracts from their biomass in order to evaluate their potential as a biostimulant for rice (Oryza sativa L.) plants. Seed inoculation and foliar application of extracts stimulated plant development. Shoot length in seedlings 7 days after germination was increased after the application of Syn 16 aqueous extract at concentration of 0.5 g/L. Shoots of 30-day-old plants increased in length with the application of Syn 16 and Syn 90 strains, regardless of the tested concentration, while root length was increased by Syn 16 (at both concentrations - 0.1 and 0.5 g/L) and Syn 90 (0.1 g/L). Regarding shoot dry weight, increases of up to 36 % were detected with the Syn 16 strain at concentration of 0.5 g/L. With the Syn 90 strain at a concentration of 0.5 g/L, the increase was 27 %. Furthermore, root dry weight was 43 % and 35 % higher than control plants after the application of Syn 16 and Syn 90, respectively (both at 0.5 g/L concentration). At the maturity stage, application of Syn 46 strain (0.5 g/L concentration) increased 11 % the number of full seeds per panicle when compared to control condition. Our results demonstrate the ability of microalgae extracts in stimulating the development and seed production of rice plants.