Induction of symptoms pre-harvest using the ‘passive method’: An easy way to predict bitter pit

• A new ‘passive method’ is presented for bitter pit prediction in ‘Golden’ apples.
• The accuracy of the ‘passive method’ was similar to that of Mg infiltration and ethephon dipping.
• The ‘passive method’ takes less time and inputs are less demanding.
• The method could be useful for commercial purposes.

An effective method for predicting bitter pit incidence implemented before harvest could be a useful instrument for both the fruit industry and growers. Between 2009 and 2011, various methods for the prediction of bitter pit were evaluated at 60, 40, and 20 days before harvest (dbh) and at a commercial harvest in ‘Golden Smoothee’ apples. Four methodologies, two new ones (the development of natural bitter pit before harvest through the ‘passive method’ and bagging detached fruit before commercial ripening), and two of known efficacy under other conditions (infiltration with magnesium salts and maturity enhancement with ethephon dips) were assessed. To estimate the predictive accuracy of each method, bitter pit-like symptoms were related to the postharvest presence of bitter pit. The ‘passive method’ assesses bitter pit-like symptoms that appear naturally in fruit once they are picked from the tree, and left at room temperature during its evaluation. The ‘passive method’, as well as the infiltration with magnesium salts and ethephon dips, recognized bitter pit-like symptoms approximately 5–7 days after sampling (at 40 dbh) and showed significant correlation with the incidence of bitter pit after three months of cold storage. The ‘passive’ and ‘ethephon’ methods were also validated over two additional seasons in 30 and 16 different orchards, respectively. The results of these validations supported the efficacy of using the ‘passive method’ as the main method for predicting bitter pit, without having to use either reactive products or specialized equipment.