Effect of High Temperature Treatments on Growth of Penicillium spp. and their Development on ‘Valencia’ Oranges

Abstract

The effect of time (up to 24h) and temperature (40 to 55°C) has been evaluated on in vitro growth of Penicillium digitatum and Penicillium italicum on potato dextrose agar plates or on ‘Valencia’ oranges ( Citrus sinensis), previously inoculated with those pathogens. The effect of treatment on the fruit quality parameters has also been evaluated. In vitro, at 40 and 45°C, an exposure of 24h was required to inhibit subsequent mycelial growth of both pathogens during incubation for 1 week at 25°C. However, at 50 and 55°C, only 18 or 9h (6h for P. digitatum), respectively, were needed to achieve the same effect on both pathogens. Inoculated fruit was exposed for 18h at 40°C then stored for 5 days at 5°C plus 7 days at 20°C, and the experiment was repeated at three locations and over two fruit seasons. This curing regime controlled both pathogens effectively. Concerning quality changes, after cold storage (5°C), treated fruits showed a significant reduction in acid content and a slight delay on skin yellowing, on softening, and on weight losses, compared to the control fruits. These results suggest that the curing treatment could be a non-chemical alternative to the postharvest fungicides now used to control citrus green and blue moulds.