Abstract
BackgroundRubus is a large and taxonomically complex genus exhibiting agamospermy, polyploidy and frequent hybridization. The objective of this work was to elucidate rDNA disrtibution pattern and investigate genomic composition of polyploids in 16 Rubus taxa (2n = 2x, 3x, 4x, 8x) of two subgenera Idaeobatus and Malachobatus by ISH method.ResultsThe basic Rubus genome had one 45S rDNA locus, and all the polyploids (except R. setchuenensis) had the expected multiples of this number. Diploid and tetraploid Rubus taxa carried two 5S rDNA, whereas the triploid and octoploid species only had three. The duplicated 45S rDNA sites tended to be conserved, whereas those of 5S rDNA tended to be eliminated after polyploidization. The accession R03-20 was an autotriploid R. parvifolius, while R03-27 and R03-57 were naturally-occurred triploid hybrids between R. parvifolius and R. coreanus. GISH results suggested that R. parvifolius had close relationship with polyploids from Malachobatus.ConclusionsThe polyploids from Malachobatus were probable allopolyploid. In addition, Rubus parvifolius might be involved in hybridization, polyploidization and speciation of some Idaeobatus and Malachobatus species.
Highlights
Rubus is a large and taxonomically complex genus exhibiting agamospermy, polyploidy and frequent hybridization
Number and localization of 45S and 5S Ribosomal DNA (rDNA) sites In either diploid or polyploid species, 45S rDNA sites localized at the terminal regions, and 5S rDNA sites were localized on proximal or sub-terminal region of the short arms (Figures 1 and 2, Table 1)
The three taxa, R. ellipticus (R01-7), R. ellipticus var. obcordatus (R01-2), and R. pinfaensis (R01-22), had two 45S rDNA sites on terminal chromosomal regions of chromosome 3. 5S rDNA sites localized on the proximal region of short arms of chromosome 5 in R. ellipticus and R. pinfaensis, but existed at sub-terminal regions of chromosome 5 in R. ellipticus var. obcordatus (Figures 1 and 2B,C and E)
Summary
Rubus is a large and taxonomically complex genus exhibiting agamospermy, polyploidy and frequent hybridization. The objective of this work was to elucidate rDNA disrtibution pattern and investigate genomic composition of polyploids in 16 Rubus taxa (2n = 2x, 3x, 4x, 8x) of two subgenera Idaeobatus and Malachobatus by ISH method. Rubus Linnaeus (Rosaceae) has long been deemed taxonomically challenging due to its propensity for agamospermy, polyploidy and frequent hybridization [1]. This genus is divided into 12 subgenera, with numerous infrageneric sections and series [2,3,4], containing several hundreds of sexual species to perhaps thousands of apomictic microspecies [5,6,7].
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