SUMMARYDNA C values were determined for eighteen natural populations of Dactylis glomerata L. collected from various sites in Europe to examine the extent of intraspecific variation in C value and how this variation may be related to latitude and altitude of origin. A sub-set (8) of these populations represent an altitudinal transect (350-1120 m) in northern Spain whilst the remainder represent a latitudinal range (38-53-57-47 °N), Preliminary experiments established optimum acid hydrolysis times for the Feulgen reaction of 62 min and 20 min for D. glomerata c\. S26 and the standard Hordeum vulgare L. cv. Sultan (C = 5-6 pg), respectively. The data emphasize the necessity of using the optimum hydrolysis time for both the standard and unknowns for C value determination, whether using 5 M HCl at 25 °C or 1 M HCl at 60 °C. This procedure has not been followed in the majority of published estimates of C value.Seventeen of the natural populations were tetraploid (2« = 4,v = 28) whilst the southernmost population was diploid {2u = 2x = 14), The 17 tetraploid populations exhibited a 28-7 "o variation in DNA C value, ranging from 4-35 to 5-60 pg, whilst the C value of the diploid population was 3-3 pg. There was neither a significant relationship between the C value and latitude of origin of the 10 populations which comprised the latitudinal transect (1 diploid and 9 tetraploid) nor with the tetraploids alone. However, the C values of the eight populations which formed the altitudinal transect in the Galicia mountains in N. Spain were negatively correlated with their altitude of origin. Possible reasons for this relationship are discussed.

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