Chemical Profiling and Bioactivity of Microalgae Extracts for Enhancing Growth and Anthracnose Resistance in the Common Bean (Phaseolus vulgaris L.)

The present study aimed to chemically profile the hydroalcoholic extracts from the microalgae (MEs) <i>Nannochloropsis oculata</i>, <i>Phaeodactylum tricornutum</i>, <i>Tetradesmus obliquus</i>, and <i>Tetraselmis tetrathele</i> and evaluate their effects on the development of <i>Colletotrichum lindemuthianum</i> and anthracnose symptoms, as well as on the initial growth of bean plants. For this, MEs were analyzed using UPLC coupled with a mass spectrometer, allowing the identification of peaks and annotation of potential metabolites. Fungal mycelial growth was assessed seven days after inoculation, and conidial germination was measured 72 h after incubation, using ME concentrations of 0, 0.1, 0.5, and 1.0 mg·mL^-1. Bean seeds of the IPR Uirapuru cultivar were sown and treated with 3 mL of extracts at four time points: at sowing and 72 h after each previous treatment. After 11 days of cultivation in a growth chamber, the plants were divided into two groups: one for anthracnose control assessment and the other for evaluating growth promotion by MEs. Plant length as well as fresh and dry weights of shoots and roots were determined, leaf pigments were quantified, and anthracnose severity was assessed using a diagrammatic scale. The UPLC analysis identified 32 compounds in the extracts of the four microalgae, belonging to different chemical and functional groups, with lipids being the most significant fraction. The extracts exhibited variability and diversity in chemical composition depending on the microalgal species. MEs did not affect mycelial growth yet increased the germination of <i>C. lindemuthianum</i> conidia, regardless of the dose or species used. Anthracnose severity was not affected by the microalgae extracts. Regarding growth promotion, the extracts showed varying effects but generally increased shoot and root length, fresh biomass, and leaf pigment content.