Application and evaluation of probiotics against red rot disease in Pyropia

Biocontrol has been widely used in crop disease control, but rarely in algae. In this study, two Pseudoalteromonas piscicida strains (P3 and P6), which have an antagonistic effect on the growth of Pythium porphyrae, were used for the red rot disease control in Pyropia. The safety and antagonistic efficiency of P3 and P6 to Pyropia yezoensis thalli were tested by immersion. Results showed that thalli immersed with P3 or P6 grew normally without pathological changes. The inhibition effect of P3 and P6 against red rot disease was tested by experimental infection, and the disease spots were significantly inhibited in P3 and P6 treated groups, with inhibition rates of 42.81%-74.35% and 60.33%-91.11%, respectively. Additionally, the P6 treatment combined with air-drying was investigated to test the application in production. The infected Pyr. yezoensis thalli immersed with 107 CFU/mL P6 for 3 min and then air-dried for 1 h could significantly inhibit the development of red rot disease, with inhibition rates over 77.23%. These results indicate that P3 and P6 can inhibit Pyt. porphyrae infection in Pyr. yezoensis, and apply to control red rot disease combined with air-drying. Thus, this research provides an effective approach for the red rot disease control, and reveals new insights into algal disease prevention and biocontrol methods.