Nuclear DNA content in twelve species of Alstoemeria L. and some of their hybrids

Nuclear DNA content (2C-value), estimated through flow cytometry using propidium iodide (PI), was shown to vary from 36.5 pg to 78.9 pg among 29 accessions of 12 Alstroemeria species (2n = 2x = 16). The extremes were found in A. magnifica ssp. magnifica and in A. ligtu ssp. simsii, both belonging to the Chilean species group. The four Brazilian species exhibited less variation in nuclear DNA content (49.8-56.4 pg), than the eight Chilean species (36.5-78.9 pg). Nuclear DNA content was positively correlated (r = 0.92, n -7, P < 0.01) with the total chromosome length. It was also positively correlated (r = 0.85, n = 5, P < 0.01) with the length of C-bands, when only the Chilean species wee considered. When both karyotype parameters, length of non-C-banded chromosome regions (x) and length of C-bands (y) were determined, it was possible to predict the nuclear DNA content (z) with the formula z = 0.65x+1.31y-0.45 (R2 = 0.97, P = 0.004). The DAPI fluorescence of most accessions was proportional to the PI fluorescence (r = 0.98, P < 0.001), except for one accession of A. ligtu, that had a relatively high PI/DAPI ratio (1.88). The PI/DAPI ratios of the Brazilian species were lower (1.59-1.67) than those of the Chilean species (1.68-1.88), which might reflect a difference in base pair composition. Four groups of species could be distinguished on the basis of fluorescence values. Diploid interspecific hybrids were shown to have a DNA content intermediate to the values of the parents involved. Both the PI and the DAPI fluorescence values of these hybrids approximated the mid parent values. Tetraploids, derived from setting of diploids, had PI and DAPI fluorescence values that were twice that of the diploid hybrids. It was possible to distinguish aneuploids from euploids based on fluorescence values.