Karyotype and Nuclear DNA content of Six Species of Astragalus (Leguminosae)

L.P. DOPCHIZ,E.GÓMEZ-SOSA AND L. POGGIO

CYTOLOGIA

UNIV TOKYO CYTOLOGIA

Año: 1995 vol. 60 p. 329 - 335

0011-4545

The genus Astragalus L. (Leguminosae-Galegeae) is remarkably wide-spread, with about 2500 species worldwide except for Australia and New Zealand. The basic numbers reported for the genus Astragalus are x = 6, 8, 11, 12, 13, 14 and 15 (Ledingham and Fahselt 1964, Spellenberg 1976, Ashraf and Gohil 1988). In Old World species, the basic number x = 8 and polyploidy are frequent. The other basic numbers are common in New World species but polyploidy here is rare (Ledingham 1960, Ledingham and Fahselt 1964, Ledingham and Pepper 1973, Spellenberg 1976, Davina and Gomez-Sosa 1993). Several hypothesis have been advanced to explain the origin of the different basic numbers in Astragalus (reviewed in Spellenberg 1976). The preponderance of species with x = 8 found also in related genera suggests that the direction of chromosome change has been from x = 8 to the others (x= 11 to x = 15), perhaps through polyploidy, followed by loss of a few chromosomes. The basic number of x = 6 was reported for a single Himalayan species by Ashraf and Gohil (1988). These authors suggest that x = 6 was derived from x = 8 by aneuploid loss of chromosomes. Evoluti­onary relationship within the genus inferred from nucleotide sequence variation in nuclear ribosomal DNA also argues that the direction of change appears to be from x = 8 to higher numbers (Wojciechowski et al. 1993). These authors suggest that if the New World aneuploid series arose by descending aneuploidy from a tetraploid x=16 or by both ascending and descending aneuploidy from an ancestor x=12, remains uncertain.