Development of antagonistic yeasts for controlling black mold disease of onion

Abstract Background The present study aimed to examine the biocontrol efficacy of 28 yeast isolates against Aspergillus niger, the common pathogen of onion black mold disease. The antagonistic potential of yeast isolates against A. niger growth was investigated using a dual culture technique. Results Five yeast isolates, including 8 and 11, showed the highest inhibition effect on the mycelial growth of A. niger. Molecular analysis using 16S RNA identified strains 8 (AUN-AH14) and 11 (AUN-AH23) as Galactomyces geotrichum (JQ713185.1) and G. geotrichum (DQ849321.1), respectively. The culture filtrates of AUN-AH14 and AUN-AH23 at percentage concentrations of 20, 40, 60, and 80 were tested against the growth of A. niger. As a result, the lowest dry weight of the pathogen was obtained with culture filtrates of the two strains at concentrations of 60 and 80%.. Treatment of onion bulbs with formulation of antagonistic yeast isolates AUN-AH14 and AUN-AH23 and their corresponding cultural filtrates at 80% concentration significantly reduced the severity of black mold disease relative to the controls. Conclusions The most significant reduction in black mold severity was proved in yeast formulations of AUN-AH14 and AUN-AH23, followed by their cultural filtrates (CF-AUN-AH14 and CF-AUN-AH23). The shelf life of formulated yeast isolates began to gradually deteriorate after 5 months of storage at 4 °C.