Segregation in New Allopolyploids of Nicotiana

G ENETIC segregation in synthetic allopolyploids of the genus Gossypium has been described in several earlier papers by the author and his colleagues (see GERSTEL and PHILLIPS 1958, for a summary). We had found in that genus that allopolyploids produced from two very closely related species segregated like autopolyploids, i.e. they gave approximately 5: 1 ratios for crosses of the duplex type ZZzz to recessive testers. In contrast, very little segregation occurred where the two parents of an amphiploid belonged to different sections of the genus; such amphiploids behaved like classical allopolyploids. From still other amphiploids intermediate ratios had been obtained. In some amphiploids the ratios differed somewhat from locus to locus, but their averages reflected in a quantitative fashion the taxonomic affinity of the two parent species which were combined in the particular amphiploid. Herein lay the main interest of the method, specially when the argument was inverted and the relationship between two species assessed quantitatively from the segregation frequencies of their amphiploid. This paper commences a series of similar studies on segregation in synthetic allopolyploids of the genus Nicotiana.