Exploitation of some Egyptian marine algal species in controlling bacterial soft rots in onion bulbs

The potential use of three marine algal powders; Corallina mediterranea, Pterocladia capillacea, and Hormophysa triquetra was assessed as bio-stimulants and growth promotors of onion bulb against Burkholderia cepacia, and Pectobacterium carotovorum; the infection agents of onion soft rots; the most dangerous storage disorders that cause economic losses in onion bulbs. The potential of algal powders to suppress onion soft rot was individually assessed in an open-air pot experiment. Applying algal powders enhanced the suppression of disease in onion bulbs caused by either P. carotovorum or B. cepaci that being extended to eight months bulb storage after harvesting. The most effective algal powder was H. triquetra, expressed by the highest decrease in the disease incidence with both tested pathogens. Moreover, soil amendment of all algal powders has increased the yield per treated pot with both pathogen treatment sets. The high content of carbohydrates and total protein in the algal powder is suggested to promote the onion bulb development especially for H. triquetra treatment. The algal powder enhanced the decrease in lipid peroxidation (Lip), increased the activity of PolyPhenol oxidase, Peroxidase, and total phenols in the bulbs as compared to pathogen control.. In conclusion, the used algal powders in this study have shown strong bio-safety suppression and can be used as eco-friendly bio-inducers for defense mechanisms in controlling onion bulbs soft rot diseases.