Effect of cool storage duration on ripening initiation of 'Angelys^®' pear fruit

Winter pears initiate ripening following exposure to room temperature (RT, 20°C), after a chilling period. The number of days required for pear fruit to fully ripen varies mainly depending on cultivar and duration of low temperature storage. However, the longer the time in cold storage, the faster the rate of post-storage ripening. This study aimed to correlate ripening of 'Angelys^®' pear fruit with different chilling periods. The correlations of ripening were performed by using measurements of physiologically-related processes (soluble solid concentrations, firmness and titratable acidity) and molecular analyses. Fruit harvested at three different times (185, 192 and 199 days after bloom, DAFB) were separated into distinct lots with the same maturity (with similar chlorophyll content, measured non-destructively using IAD). Each lot was analysed after postharvest ripening for 6 days at RT, following cool storage (0°C) for 0, 1, 2 and 3 months. Results indicated that ripening is halted in the non-chilled pears and initiated in the majority of pears stored for 1, 2 and 3 months independent of the harvest time. Unexpectedly, among the 3 months chilled pears, harvested at 199 DAFB, some fruit were showing a strong delay of ripening (unripe group). The latter lot was compared with the nonchilled pears and those stored for 3 months but showing typical ripening traits (ripe group) by using an RNAseq approach. In the three comparisons, there were 2498 differentially expressed genes. Many of the genes differentially expressed in each comparison showed expression patterns related to cool storage. However, others showed patterns that were related to fruit ripening, such as those encoding for ethylene receptors and cell wall modifying enzymes. In addition, only in the ripe group an up-regulation of genes involved in chromatin remodelling was observed; such genes have been previously associated with the competence to ripen.