Efficacy of gaseous ozone treatment on spore germination, growth and fumonisin production by Fusarium verticillioides in vitro and in situ in maize

The objective of this study was to examine the effect of gaseous ozone (O3) at 100 and 200 ppm concentration, applied for 30 or 60 min (flow rate 6 L/min), on in vitro germination, growth and fumonisin (FUM) production by Fusarium verticillioides at different water activity (aw) conditions and the in situ effects after O3 treatment on fungal populations and FUM contamination of maize inoculated with F. verticillioides and stored at different marginal aw levels (0.92, 0.88) for 15 and 30 days. In vitro conidial germination appeared to be completely inhibited immediately after treatment (24 h) regardless of O3 exposure and aw level used. However, storage of spores resulted in recovery of germination over 8-10 days incubation to control levels at 0.98 and 0.94 aw. FUM production (FUMB1, FUMB2, FUMB3) after the germination of conidia treated with 100 or 200 ppm O3 was significantly higher than the controls. There was little effect of O3 treatment on mycelial extension of F. verticillioides. However, storage of the O3 exposed colonies for 10 days showed FUM contamination to be reduced when compared with the untreated controls. Maize grain adjusted to marginal aw levels (0.88, 0.92 aw) for growth of this mycotoxigenic species was inoculated with F. verticillioides conidia and exposed to these concentrations of O3 for 60 min. Immediately after treatment, the total fungal CFUs on the maize grain was significantly reduced. After storage for 15 and 30 days production of FUMB1 + FUMB2 was not detected in the control and O3 treatments at 0.88 aw. At 0.92 aw, there was FUM production in the controls but little in the O3 treatments. The implications of using gaseous O3 as a control strategy for minimising mycotoxin contamination of cereals are discussed.