Abstract:

Citrus blue mold is a prevalent disease affecting citrus fruits during storage and transportation, leading to serious economic losses. Iturins exhibit potential for controlling citrus blue mold disease, but its yield remains low. This study conducted the response surface optimization on 3 key factors influencing the production of iturins by Bacillus subtilis NIP3, and analyzed the efficacy of iturins against Penicillium italicum both in vivo and in vitro. The results from response surface analysis showed that the optimal concentrations of glucose and L-glutamate, as well as temperature, were 30 g/L, 6 g/L, and 33℃ respectively for maximizing iturin production by B. subtilis NIP3. Under these optimized conditions, the yield of iturins reached 721.33±3.72 mg/L, an increase of 51.59% compared to pre-optimization levels. The detection method significantly influenced the control efficacy of iturins in vitro. The Oxford cup diffusion method revealed that the lowest effective concentration of iturins inhibiting P. italicum growth was 312.5 μg/mL. Furthermore, the effective concentration (EC₅₀) inhibiting spore germination and mycelium growth were determined to be 29.11 μg/mL and 22.80 μg/mL respectively when measured via hollow slide method and mycelium dry weight method. Results demonstrated that while at a concentration of 10 mg/mL, iturins exhibited superior preventive effects over therapeutic effects against citrus penicilliosis, with an incidence inhibition rate reaching up to 100%. This study provides a scientific foundation for developing biocontrol agents targeting citrus blue mold disease.

Key words: citrus blue mold disease, Bacillus subtilis, iturin, response surface optimization, control effect