Phycobiliproteins from the cyanobacterium Anabaena minutissima for the Rhizoctonia solani control and tomato growth-promotion

The principles of integrated pest management give priority to natural alternatives to ensure a high level of protection of human and animal health and the environment. Cyanobacteria are efficient producers of bioactive compounds such as phycobiliproteins that have shown multiple biological activities including antimicrobial, antiviral, anticancer, antioxidant, and anti-inflammatory activity in humans. Only in recent years, few studies have reported their use against fungal plant pathogens. The phycobiliproteins used in this study were extracted from the cyanobacterium Anabaena minutissima that was isolated from a coastal humid basaltic wall in Fuerteventura Island. They were firstly characterized by FT-IR and FT-Raman spectroscopies and then applied to tomato seeds for testing their activity against the soilborne pathogen Rhizoctonia solani and evaluating the biostimulant effect on tomato seedlings. Our results showed that seeds treatment with different PBPs doses increased seedling emergence over time in soil infected with R. solani, reduced the disease severity, and enhanced plant dry weight in comparison to the infected control, under greenhouse conditions. Additionally, a deeper investigation carried out in agar showed that seed treatment stimulated seed germination and epicotyl and hypocotyl seedling length. Proteins extracted from epicotyl and hypocotyl after PBPS seed treatment reduced R. solani mycelium growth and showed increased chitinase and glucanase enzymatic activities compared to untreated control. Biostimulant effects after seed treatment were observed for several vegetative parameters such as emergence, fresh and dry weight, leaf content of chlorophyll a and b, carotenoids, and micronutrients such as Fe, Mg, Mn, and Zn. PBPs also showed hormone auxin- and gibberellin-like activities. In conclusion, PBPs from A. minutissima are promising bioactive compounds useful for the control of fungal plant pathogens and biostimulant activity.