Impact of interspecific hybridization of T. pratense × T. medium and backcrossing on genetic variability of progeny

Abstract

Red clover (Trifolium pratense L.) is a high-quality fodder crop which has been hybridized successfully with its wild relative zigzag clover (T. medium L.). The aim of this study was to evaluate the genetic impact of interspecific hybridization and subsequent repeated backcrossing on the variability within hybrid progeny genomes. Nuclear DNA content of 800 and 753 hybrid plants from F7/F8 and F8/F9 generations, respectively, was measured by flow cytometry. Resulting values were converted to estimated chromosome counts, which were successfully validated on a sample of 28 plants by counting mitotic chromosomes. The two generations showed a similar distribution of various chromosome counts ranging from 22 to 47 chromosomes. In total, 24.0% and 34.3% of plants from the two generations had different numbers of chromosomes from their parental plants. Variability within the hybrid population was assessed by fluorescent in situ hybridization using rDNA probes. Individual plants had a pattern of 5S and 45S rDNA loci rather more similar to that of T. pratense than of T. medium. Numbers of chromosomes with clusters of 5S rDNA ranged from 6 to 14 while those of 45S rDNA varied between 4 and 13. Individual arrangements were almost unique, and some plants possessed also novel formations which were not present in any of the parental species, such as a cluster of 5S rDNA surrounded by 45S rDNA clusters or a 45S rDNA cluster surrounded by 5S rDNA clusters. This suggests complex rearrangements connected with post-hybridization stabilization of hybrid genomes.

Keywords

• cytology
• fish
• hybrids
• rdna
• red clover
• zigzag clover