A palindromic sequence on chromosome 4 of peach (Prunus persica L. Batsch) is flanking a large deletion related to a Slow Ripening Phenotype

Maturity date (MD) represents one of the main goals of the peach breeding programs worldwide with the aim to extend the harvest calendar. A major QTL linked to the trait was previously identified in peach and other stone fruits on LG4, and NAC genes were identified as the best candidates for the MD control. Here, a bud mutation affecting MD was found in a tree of the nectarine ‘Caldesi 2000′. The original variety (CW), its mutated sport (CM) and a segregating progeny obtained by selfing of CM was used to characterize the trait at phenotypic and molecular level. A panel of markers spanning the MD region was developed and a few recombinant plants were identified. A Non-ripening phenotype was observed in seedlings homozygous for one of the haplotypes, an effect probably caused by a large deletion of about 26 kb inactivating two transcription factors belonging to the NAC family (PpNAC072 and PpNAC1), similar, but independent, to a previously reported mutation associated to a slow ripening trait. The presence of palindromic sequences in the regions flanking the deletion may explain the occurrence of this phenomenon. The putative silencing of two members of the NAC family further supports the importance of these transcription factors in determining the MD phenotype. Further research is needed to elucidate functions and interactions between PpNAC072 and PpNAC1 in controlling the MD trait in peach and to determine the hierarchical expression of genes controlling fruit ripening.