Effects of Temperature and Relative Humidity on the In Vitro and In Vivo Radial Growth of Penicillium italicum and on the Biocontrol Activity of Pichia guilliermondii, Strain Z1

The objective of this study was to assess the effect of temperature (5-25°C) on the ‘in vitro’ and ‘in vivo’ growth rates of Penicillium italicum and to determine the combined effect of temperature and relative humidity (45 to 100%) on lesion size of this pathogenic fungus on Valencia late oranges, either alone or in combination with the antagonistic yeast strain Z1 of Pichia guilliermondii Wickerham. Statistical analysis showed a significant effect of temperature on the ‘in vitro’ and ‘in vivo’ radial growth of P. italicum with the maximum growth observed at temperature of 25°C. In both cases, no growth was observed at a temperature of 35°C. These factors had a significant effect on P. italicum lesion size when it was applied alone on Valencia late oranges and insignificant when yeast strain Z1 was applied 24 h before P. italicum inoculation. Our results confirm previous ‘in vitro’ findings that aw has a greater influence than temperature on P. italicum growth and highlight that the strain Z1 showed high antagonistic potential against this pathogen over a range of temperature-relative humidity regimes favouring P. italicum development.