Cyanobacterial extracts as biostimulants for hydroponically-grown basil

To meet the challenges posed by the growing global population and climate change, farmers are called to increase global food production reducing chemical inputs and environmental impacts. Nowadays, the use of microalgae in agriculture is attracting the interest of growers and agrochemical industries; however, the wide genetic variability of these microorganisms has yet to be fully explored. Few biostimulants based on microalgae, mainly Chlorella and Arthrospira spp., are currently on the market. In this work we evaluated the biostimulant activity of five extracts obtained from cyanobacteria belonging to the Nostocales, Oscillatoriales and Synechococcales, on hydroponically grown basil (Ocimum basilicum L.). Plants were cultivated in floating systems on ½ Hoagland medium for 28 days and treated weekly with foliar applications of the extracts. Two commercial biostimulants were also tested for comparison: an Ascophyllum nodosum extract and an animal protein hydrolysate. Three of the tested strains, administered at the concentration of 1 g (extract dry weight) l -1 were the most effective in promoting plant growth, with an increase in plant fresh and dry weight of about 30% and 40%, respectively, compared to the untreated control; moreover, these plants presented one node more than the untreated controls and the number of leaves consequently increased by more than 20%. The A. nodosum extract showed no significant effects while the protein hydrolysate slightly depressed plant growth compared to the control. Our results demonstrate that foliar application of cyanobacterial extracts may strongly enhance plant growth and yield and could be used for improving the sustainability of agricultural fertilization practices.