The Genetic Components Involved in Sensing Chilling Requirements in Apricot

Abstract

Most apricot (Prunus armeniaca L.) varieties are known for their high sensitivity to environmental conditions, particularly for exposure to chilling. Insufficient chilling will result in difficulties breaking dormancy, developing normal flowers, and producing high-quality fruit. Taking advantage of a unique collection of local and introduced apricot varieties, combined with the relatively hot Israeli winter, provided an opportunity to identify genetic components responsible for determining chilling requirements in apricot. The main QTL identified in an F1 population segregating for chilling requirements is located on linkage group 1 (Olukolu et al. 2009), the same as the evg phenotype that was mapped in peach (Prunus persica L.) and the site where six DAM genes were identified and characterized (Bielenberg et al. 2004; Bielenberg et al. 2008). In addition, a ParSOC1-like gene was mapped to linkage group 2 (LG2) and was colocalized with a minor QTL identified in the population studied (Olukolu et al. 2009; Trainin et al. 2013). ParSOC1 is expressed in a diurnal manner and reaches its peak toward the end of the night. A SSR located in the 5′ UTR of the gene revealed high polymorphism among different accessions in the apricot collection and was used to associate certain ParSOC1 alleles with chilling requirements. The data suggest that ParSOC1, or a gene in its close proximity, might be involved in determining chilling requirements in apricot. Two SOC1-like genes were also identified in the apple (Malus domestica Borkh.) genome. Like in peach and apricot, the apple genes also have an SSR (CT)_n in a similar position and show high polymorphism in the Israeli apple collection. These results suggest that the presence of the SSR in SOC1-like genes preceded the split between Malus and Prunus in the course of Rosaceae family evolution.