Maturity matters: Transcriptomic insights into how ripening shapes soft scald susceptibility in ‘Red Aroma’ apple fruit

The physiological disorder soft scald may cause losses in apple fruit storage. This study aimed at understanding the interplay between fruit maturity at harvest and storage temperature on soft scald development in the susceptible cultivar ‘Red Aroma’. Fruit harvested late and subsequently stored at −0.5 °C developed the significantly highest soft scald incidence. Overall ethylene and CO2-production was reduced in late harvested fruit stored at −0.5 °C, while fruit from the early harvest showed a cold-induced ethylene increase under the same storage conditions, suggesting an active cold-acclimation response. Clustering of RNA sequencing data and overrepresentation analysis revealed that transcripts involved in cell wall modification, ripening-associated signaling, antioxidant defense system and secondary metabolism were upregulated in late harvested fruit at harvest as well as soft scald-affected fruit after storage. In contrast, early harvested fruit at harvest and disorder-free fruit after storage showed higher expression of transcripts associated with abiotic stress resistance, such as leucine-rich repeat receptor-like kinases, protein kinases with tetratricopeptide repeat domains, and auxin response factor, indicating a potential link between early maturity and enhanced cold tolerance in ‘Red Aroma’ apple fruit.