Nuclear DNA content variation within the genus Daucus (Apiaceae) determined by flow cytometry

• Evaluation of DNA content in 67 Daucus accessions originating from various regions of the world.
• First estimation of genome size for five wild species and eight D. carota subspecies.
• Nuclear DNA content varied among Daucus species.
• Relatively high intraspecific variability in genome size existed among wild D. carota subspecies.
• Genome size analysis can be a complementary tool for phylogenomic studies and taxonomic classification of Daucus accessions.

The genus Daucus (Apiaceae) comprises species from around the world, covering a wide climatic range, and showing great morphological plasticity. Both cultivated and wild forms are described within the genus. The aim of the present study was to estimate the genome size variability in the collection of diploid Daucus species differing in chromosome number (2n = 18, 20 or 22) and originating from various regions of the world. In total, the 2C DNA content in 19 accessions of nine wild Daucus species, as well as in 22 wild and 26 cultivated accessions of Daucus carota L. was measured by flow cytometry. The 2C DNA content varied over 3-fold, from 0.920 pg in D. carota subsp. maximus (2n = 18, Spain) to 3.019 pg in D. littoralis (2n = 20, Israel). The interspecific genome size differences within wild Daucus species were pronounced, e.g. D. carota (2n = 18, Greece) possessed 0.940 pg/2C DNA, D. broteri (2n = 20, Cyprus) 2.218 pg/2C and D. montevidensis (2n = 22, South America) 1.295 pg/2C. In the group of 22-chromosome Daucus species, high similarity in nuclear DNA content among different accessions of one species was observed, in contrast to the 20-chromosome Daucus species, suggesting possible taxonomical misclassifications of accessions within the latter group. The nuclear DNA content of non-cultivated forms of D. carota varied from 0.920 pg/2C in subspecies maximus (Spain) to 1.154 pg/2C in subspecies halophilus (Portugal), which reflects 20% difference. In turn, in the group of cultivated carrots we observed a high homogeneity among the studied accessions, the 2C DNA content ranged between 0.950 pg (‘Kuroda type II’, China; ‘Imperial Long Scarlet’, Japan; ‘Koral’, Poland) and 0.977 pg (‘Cape Market’, South Africa). The mean 2C value calculated for both wild and cultivated forms of D. carota amounted 0.973 pg.