Abstract: The objective of this study was to evaluate the effect of Bacillus amyloliquefaciens NCPSJ7 against green molds on postharvest navel oranges and the underlying mechanism. The antifungal effect of cultures of NCPSJ7 was determined by the Oxford cup method and disease incidence, disease resistance-related enzymes activities and antioxidant capacity in oranges artificially inoculated, treated with the fermentation broth and inoculated with Penicillium digitatum were determined. The results indicated that a high NCPSJ7 concentration significantly inhibited the growth of P. digitatum on navel oranges in vitro (P < 0.05). The diameter of inhibition zone of 1 × 108 CFU/mL NCPSJ7 was 3.50 cm, which was twice higher than that observed at 1 × 105 CFU/mL (1.75 cm). In vivo tests showed that the antagonist NCPSJ7 could colonize rapidly the wounds in oranges within 24 h after inoculation for space and nutrient competition to inhibit the growth of P. digitatum. Moreover, compared with single P. digitatum and the control group, NCPSJ7 combined with P. digitatum significantly decreased disease incidence and lesion diameter, increased the activities of polyphenol oxidase (PPO), peroxidase (POD), chitinase (CHI) and β-1,3 glucanase (GLU), and promoted the increase in reducing power and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity as well as total phenol and total flavonoid contents. These observations indicated that B. amyloliquefaciens NCPSJ7 could be used as a biocontrol agent against P. digitatum on postharvest oranges.

Key words: navel oranges; antagonism; Penicillium digitatum; antioxidant capacity; action mechanisms