Haplotype-resolved genome assembly advances genetic understanding of trait diversity in Phalaenopsis orchids

As an important ornamental crop, Phalaenopsis orchids exhibit extraordinary trait diversity with unclear genetic bases. Here, we present a haplotype-resolved, chromosome-level genome for an aneuploid cultivar 'Santiago'. We reveal pervasive variation in the number and sequence among homoeologous genes. When serving as a reference, this genome facilitates the genetic understanding of trait variation in a hybrid population that is highly representative in trait polymorphisms. Specifically, nucleotide polymorphisms in a potential long-distance enhancer and the consequential expression variation of PsAGL6-2, presence/absence of PsMYB12 and b-type homoeologous gene of PsMYB2 determine lip morphology variation, presence/absence of venation-associated stripes and background pink color, respectively. Diverse functions of PsMYBx1 in repressing anthocyanin accumulation across different cultivars further enhances the color patterning diversity in Phalaenopsis. Our study provides a practical framework for using a highly heterogeneous, haplotype-resolved genome to decode phenotypic diversity and has the potential to promote marker-assisted breeding in Phalaenopsis.