A model to predict ripening capacity of 'Bartlett' pears (Pyrus communis L.) based on relative expression of genes associated with the ethylene pathway

Resistance to ripening in European pears depends on various preharvest and postharvest factors. Exposure to cold temperatures has been demonstrated to condition pears to produce endogenous ethylene and ripen. Mature green 'Bartlett' pears were exposed to 0, 5, or 10 °C for 2-14 d to induce different rates of ripening. At higher temperatures, expression of ethylene biosynthesis genes (ACS1a and ACO) and ethylene receptor genes (ETR2, ERS1a, and ETR1a) increased, while CTR1 expression decreased. Multiple linear regressions between relative expression of these genes after 0 d and fruit firmness after 6 d during ripening at 20 °C were conducted. Using K-fold cross validation and conventional validation, it appears that expression of ACO could be utilized as an early predictor of pear ripening capacity.