Analyzing the genetic relationships in Tulipa based on karyotypes and 5S rDNA sequences

Abstract

Tulips are commercially important garden and cut flowers. With numerous wild species, China is one of the distribution centers of Tulipa. It is of great significance to tulip breeding to clarify the genetic relationships between wild species and the cultivars. We conducted rDNA oligo-FISH, karyotype analysis and rDNA sequencing of eight wild species and four cultivars. The results indicated that the 45S rDNA distribution presented a typical interspecies evolutionary trend among different Tulipa sections. The differences in 5S rDNA manifested mainly in the number of loci, which ranged from two to several dozen. Surprisingly, 11 base deletions appeared in the coding region of 5S rDNA in three wild species and three cultivars. The probes we designed clearly revealed that 5S rDNA sequences containing a complete coding region are necessary in each species, regardless of whether they can be detected by PCR using universal primers. Compared with data based on phenotype and molecular markers, our results provide clearer and more stable evidence for the classification of tulips. We concluded that among the wild Tulipa species studied, Tulipa edulis is the most primitive, whereas T. schrenkii and T. tianschanica are the most similar to cultivars.