Effect of microalgal extracts from Chlorella vulgaris and Scenedesmus quadricauda on germination of Beta vulgaris seeds

Sugar beet (Beta vulgaris subsp. vulgaris) is a commercially important biennial root crop providing about 20% of the world annual sugar production. Seed quality is crucial for an adequate plant growth and it is strictly associated with the quanti-qualitative production of the crop. Unfortunately, the productivity of sugar beet is often limited by low or irregular germination in the field also due to the presence of inhibitory substances in the pericarp of the seed. In order to improve sugar beet germination process, the effect of different concentration of microalgal extracts from C. vulgaris and S. quadricauda on several indices (i.e. germination percentage GP, mean daily germination MDG, germination index GI, etc.), useful to evaluate the germination performance, was investigated. Moreover, root morphological analysis was performed by using WinRHIZO software and seedling length (SL), root surface area, total number of root tips, root diameter, root volume and lateral root were determined. The two microalgae extracts were firstly characterized by CNS, Fourier transform infrared spectroscopic analysis (FT-IR), and carbon-13 nuclear magnetic resonance (13C NMR). Beta vulgaris seeds were soaked with six different concentrations of the microalgal extracts, considering the quantity of organic carbon (Corg) in each extract: 1) Untreated = 0 mg Corg/L; 2) C1= 0.1 mg Corg/L; 3) C2 = 1 mg Corg/L; 4) C3 = 2 mg Corg/L; 5) C4 = 5 mg Corg/L; 6) C5 = 10 mg Corg/L. Our results show that these microalgal extracts exert a positive effect on sugar beet germination, making more efficient as well as regular this critical process for Beta vulgaris seeds. Among all the treatments the best results, in term of germination indices as well as root morphological traits, were reached by using C. vulgaris extract at the concentrations C2 (1 mg Corg/L) and C3 (2 mg Corg/L).