Evaluation of a preharvest bioclimatic model for predicting the risk of Low temperature disorders of stored apples in Canada and France.

Low temperature disorders (LTD), characterized by internal browning of apple flesh, can be found in apples that have been held in long-term controlled atmosphere (CA) storage. As CA storage temperatures drop below a critical level, the incidence and severity of the low temperature disorders may increase, especially if weather conditions during apple fruit development were favourable for such disorders. The growing season of 1992 in Quebec (Canada) was characterized by lower temperatures and more days with precipitations than average during the months of July and August. Vascular browning, a LTD associated with 'McIntosh' apples, caused major losses throughout storage during the winter of 1993. Using data from 1977 to 1995, a bioclimatic model, LTD-riskV1, based on air temperature and the number of days with precipitations, was developed to predict risks of vascular browning. Its predictions reflected well the inter-annual weather variability, with the highest risk predicted in 1992, followed by the 2000 growing season in Quebec. To allow risk predictions for other locations using weather data in real time, a new version, LTD-riskV2, was developed and implemented in the CIPRA (Computer Center for Agricultural Pest Forecasting) system. This version computes a daily risk index starting at the fruit set stage, which removes the limitation of using only specific months. In 2007, 'Ariane' apples in France had severe damage and losses caused by low temperature disorders. Using weather data from three different regions in France, the model was tested to see if risk predictions were adequate for those regions. Overall, the LTD-riskV2 model predicted high risks mainly in one of the region for apples grown during the 2007 season, for which high occurrence of low temperature disorders was observed. Increasing storage temperatures to ∼2.5°C (instead of the 0.5°C generally used) helps reducing the risks of low temperature disorders in CA-stored apples.