Effect of incubation temperature and relative humidity on lesion diameter of Botrytis cinerea Pers. and Penicillium expansum Link. on apple fruits.

Previous studies carried out in our laboratory demonstrated that the growth of B. cinerea and P. expansum was highly influenced by water activity and temperature in 'in vitro' conditions. Regardless the temperature, a, minimal for growth was < or = 0.89 and equal to 0.89 for P. expansum and B. cinerea respectively. The effect of incubation temperature (5-25 degrees C) and relative humidity (RH 75-98%) on the lesion diameter of two common fungi B. cinerea and P. expansum was studied and modelled in the controlled laboratory conditions in order to validate previous findings. The obtained results showed that only temperature had a significant effect on fungal growth on wounded apples. The relative humidity of air had no direct influence on growth of fungi. The part of variation explained by both studied factors is 52 and 55% respectively for P. expansum and B. cinerea. 'Lack of Fit' test was no significant for models, suggesting a greater difference between observed and predicted values. The difference between observed and predicted values was 14 and 29% respectively for P. expansum and B. cinerea. Theses results is in contradiction as compared to in vitro conditions and underlined that the humidity inside wounded apple sites is highly sufficient to start the growth of both postharvest pathogens of apples.