Intraspecific rDNA FISH-based karyological variation corresponding to the phenotypic diversity of Rosa praelucens Byhouwer

Rosa praelucens Byhouwer is a critically endangered allo-decaploid wild rose endemic to Shangri-La County in Northwestern Yunnan of China. It is rich in phenotypic variation among which flower color and size variation are most conspicuous. Except for the rich genetic diversity within the species, nothing else was known for explaining its phenotypic variation. The 5S rDNA and 45S rDNA FISH-based karyological analysis of ten significantly different phenotypes was carried out to investigate the extent of intraspecific karyological variation within the species and to probe the possible cytogenetic basis for the richness in phenotypic diversity. The results showed that besides the common decaploid phenotypes, there were a nonaploid phenotype with pinkish white and smallest flowers and an aneu-nonaploid one with smaller deep peach red but white centered flowers. The number of 45S rDNA sites among different phenotypes varied from 4 to 10, while that of 5S rDNA sites was 9 for the two nonaploids and 10 for the remaining decaploids. Furthermore, the distribution and fluorescence strength of both 45S and 5S rDNA sites varied greatly among different phenotypes. We speculated the combined effects of chromosome number variation and structure rearrangement driven by the high ploidy level might be the cytogenetic reason for the rich phenotypic diversity of R. praelucens.