Extraction of ancestral constituents of natural polyploids

Abstract

Pentaploids (2n = 5x = 35 = AABBD) were backcrossed to the hexaploids (2n = 6x = 42 = AABBDD) for extraction of the tetraploid (2n = 4x = 28 = AABB) component. Frequencies of pentaploids involving Triticum aestivum (varieties Chinese Spring, Koga, Peko, A, T. 38, Svenno), Triticum durum (varieties Carleton, Machmudy, Iumillo, Nursi, Samra), and Triticum dicoccum (variety 2 D1) were studied. In the first backcross, pentaploids were used as females and also as males, but the recovery percentages (18 % and 21 %) were similar so that the direction of crossing seemed to have no effect. There was also evidence of varietal differences: the recovery percentage varied from 3 % (from pentaploids involving A. T. 38 × Machmudy × Chinese Spring) to 32 % (from the pentaploid involving the synthetic hexaploid, Triticum durum var. Carleton x Aegilops squarrosa). The increased frequency of 14-chromosome embryo sacs in the combination involving the synthetic hexaploid might be due to the homozygosity of the tetraploid component (AABB), which is the Carleton genotype, and the greater alienation of the D genome derived from Aegilops squarrosa (2n = 14). The recovery percentage (11 %) in the second backcross involving varieties of natural hexaploids, however, was lower than the recovery percentage (18 %) following the first backcross.