Biological control of postharvest brown rot in Peach and Nectarine fruits by Bacillus subtilis (B-912)

The effects of Bacillus subtilis (B-912), as well as combination application with Ca ²⁺ and fungicide on postarvest brown rot of peach and nectarine fruits were determined. Generally the lesions on nectarine fruits developed more rapidly than that on peach fruits when stored at 25° and 15°. but lesions were smaller than tht on peach when nectarine fruits were stored at 3° for 30 d as well as followed by 2 d at 25 °. At concentration of 10 ⁶ CFU (Colony-forming Units) per ml, unwashed cells of B-912 substantially reduced brown rot with infection rates of 20% on peach and 40% on nectarine when fruits were inoculated with Monilia Fructicola following the application of biocontrol agent. At 10 ⁸ CFU per mL, B-912 completely suppressed brown rot both at 25° and 3°. Additional treatment with 2% CaCl ₂ did not enhance the biocontrol efficacy of B-912 at 10 ² - 10 ⁸ CFU/mL although CaCl ₂ significantly reduced the infection rate in the control fruits. The bacterial antagonist mixed with iprodione at 100 mg/L showed a greater control to the pathogen compared with the single ingredient. The mechanism of B-912 activity appears to involve a production of anti-fungal substances, since the culture filtrate inhibited the growth of M. fructicola in vivo and limited the spore germination in vitro.