Multidisciplinary approach provides novel insight about fruit flesh browning physiology in apple (Malus × domestica Borkh.)

Flesh browning in apple is an undesirable oxidative reaction responsible for the development of unpleasant aesthetically appearance affecting the economic value of minimal processed fruits. Browning is mainly due to the class of polyphenol oxidase (PPO) enzymes. Within the ‘Golden Delicious’ genome, 10 PPO genes were identified and located on 3 chromosomes (2, 5 and 10). On chromosome 10 one element in particular, here named Md-PPO, was further investigated and genetically mapped in two apple progenies (‘Fuji’ × ‘Pink Lady’ and ‘Golden’ × ‘Braeburn’). 25 QTLs related to 24 browning parameters have been detected using the above mentioned linkage maps: the LOD values span from 3.08 to 4.99, and explain a rate of phenotypic variance from 26.1 to 38.6%. The anchoring of these intervals on the reference apple genome identified several genes involved in polyphenol synthesis and cell wall metabolism. In the end, the expression profile of two specific candidate genes (phenylalanine ammonia lyase and polyphenol oxidase) situated up and downstream the polyphenolic pathway gain insight about the regulation of the flesh browning physiology. Md-PPO was further exploited, and two haplotypes were characterized and associated with the fruit flesh browning in apple