Ripening behavior in red flesh ‘Kissabel®’ apple fruit during postharvest

In the last few years, the cultivation of red flesh apple cultivars received great attention due to their novelty and valuable nutraceutical properties, considering their higher anthocyanin and phenols content than white flesh apple cultivars. Nevertheless, red flesh cultivars can be characterized by a low storability, being therefore prone to develop internal browning disorder. In this preliminary work, we investigated the postharvest ripening behavior of the red flesh apple R201-‘Kissabel®’, a late season cultivar, in comparison with the white pulp apple ‘Golden Delicious’, generally considered as the standard reference cultivar for apple. For this purpose, fruit were collected at commercial harvest and kept for one month at room temperature in regular atmosphere. The cortex of five apple was sampled every two days along this period. Total RNA was extracted, reverse transcribed and RT-qPCR were performed on specific ripening related genes, such as ethylene biosynthetic genes (MdACS3, MdACS1 and MdACO1) and the polygalacturonase-1 (MdPG1). Moreover, proton-transferreaction mass spectrometry (PTR-ToF-MS) was employed to quantify ethylene evolution during the stored period. In ‘Kissabel®’, ethylene started to be accumulated immediately after harvest, and one week earlier than ‘Golden Delicious’. Moreover, both cultivars showed a first peak at 9 and 16 days after harvest (DAH) and a second one at 14 and 21 DHA, respectively. Based on the expression profile of selected genes, the first peak coincided with the ripening onset. In ‘Golden Delicious’, indeed, the highest expression level, for all genes, corresponded with the maximum of ethylene production at 16 DAH. In ‘Kissabel®’ the maximum expression was instead detected two days earlier respect the ethylene burst, while the expression pattern of MdACS3 decreased immediately after harvest in both cultivars, as expected. These results represent the first step to better characterize the ripening behavior and storability of this new apple cultivar