Deoxyribonucleic Acid and the Ancestry of Wheat

Abstract

REES¹ has suggested that data relating to the DNA content of nuclei may provide a further clue regarding the parental composition of allopolyploid plants like durum and bread wheats. From Rees's results¹ it is clear that Aegilops speltoides is more likely to be the donor of the B genome of tetraploid wheat than the other members of the Sitopsis section of Aegilops. With the view of understanding: (a) the relationship between somatic chromosome length and DNA content; (b) the extent of variation in DNA content of different varieties and species of Triticum and Aegilops, we estimated the DNA content of mitotic prophase nuclei using a microspectrophotometer constructed on the two wave-length principle of Ornstein² and Patau³. We preferred prophase nuclei to interphase nuclei since inter-slide differences were less in the former. When prophase nuclei were used in measurements, we did not find chromatin diminution to the extent inferred earlier⁴. Examination of chromosome-length and DNA content indicated a definite relationship between the two^4,5. The DNA values of Triticum and Aegilops species (Table 1), however, did not lend themselves to interpretations such as those which Rees¹ could draw.