Genetic diversity and association analysis of the reblooming trait in bearded iris cultivars using SSR fluorescent markers

Reblooming is a highly desirable trait in ornamental plants as it extends the flowering period and enhances horticultural value. This study investigated the genetic relationships of 17 bearded iris cultivars, comprising nine reblooming, and eight once-flowering cultivars. Transcriptome-wide screening identified 29,800 Simple Sequence Repeat (SSR) loci from 100,391 unigenes, with an occurrence frequency of 29.68%. Dinucleotide repeats were the most abundant (69.10%), predominantly AG/CT and AT/AT motifs, while trinucleotide repeats accounted for 30.90%, mainly AAG/CTT and AGG/CCT motifs. From 110 SSR primers designed based on these loci, eight highly polymorphic primers were selected, detecting 43 alleles with polymorphic information content (PIC) values ranging from 0.5072 to 0.6986 (average 0.6228). These markers effectively distinguished between reblooming and once-flowering cultivars, enabling the construction of molecular fingerprints and a cluster dendrogram for the 17 cultivars. Association analysis revealed that one SSR marker (P2S19) was significantly correlated with the reblooming trait. Together, these findings provides valuable insights for understanding reblooming regulation and facilitate the molecular breeding of reblooming iris cultivars.