ASHS 2025 Conference

There is an urgent need to diversify high-value fruit crops in low-chill areas, especially as climate change decreases the number of chill hours in cropping areas. Apple is largely considered a temperate crop, yet a subset of germplasm exhibits strong flowering responses even after minimal chill. These genotypes originate from Israeli breeding programs, as well as heritage commercial varieties and backyard discoveries. Future breeding efforts will benefit from characterization of the genetic mechanisms that govern flowering in response to limited chill. In this study we hypothesized that examination of sequence polymorphisms and flowering associated gene sequence differences may permit grouping of low chill materials based on common mechanisms. Relatedness was examined using a series of simple sequence repeat markers (SSRs). In addition, genomic sequence from a number of low chill accessions, including Dorsett Golden, Shell of Alabama, and an early-flowering accession from Mississippi, was compared to publicly available reads from ‘Anna’ (low chill), moderate chill (‘Fuji’, ‘Gala’) and high chill (‘Honeycrisp’; ‘Antonovka’) varieties. Genomes were aligned to Golden delicious reference genome, and shared and unique variants were identified. The data show that all low and moderately low chill cultivars share common sequence polymorphisms not found in high-chill germplasm. Examination of flowering and dormancy-related genes shows common sequence polymorphisms shared within low chill materials that contrast against high chill genotypes. These include members of MADS-boxes family, Frigida family, Early bud break (AP2/ERF) family, auxin responsive factors, transcription factors DELLA family, FRIGIDA INTERACTING PROTEIN, and others. This study illuminates potential mechanisms of low-chill responses, opening opportunities for marker-assisted breeding and increased genetic diversity in development of low chill apple cultivars.