Aim of study: The Caucasian apple (Malus orientalis Uglitzk.) is distributed throughout the Hyrcanian forest. Self-incompatibility (SI) is one of the most important plant strategies to prevent self-fertilization, but the genetic basis of this system has never been studied in Caucasian apple. Investigating the genetic diversity of Caucasian apple along an elevation gradient is the second aim of this study.

Area of study: Three populations of Caucasian apple along an altitudinal gradient in northern Iran were studied.

Material and methods: Here, we evaluated the S-allele frequency and genetic diversity of three populations of Malus orientalis using SSR markers.

Main results: In total, 18 S-alleles were identified in three populations, and a positive trend was detected between S-allele frequency and altitude, which is consistent with the positive correlation with genetic diversity. Overall, the genetic differentiation among populations was high, and four distinct groups were determined among three altitudinal populations.

Research highlights: Despite the small number of individuals and low genetic diversity of the populations, the S-allele frequency of Caucasian apple in Hyrcanian forests is high, and these resources have potential use in apple breeding programs.