Pentaploids (2n = 5x = 35, AABBD) and 34-chromosome plants, obtained after the first backcross, were backcrossed to 4 varieties (Chinese Spring, Peko, Koga and Svenno) and 11 monosomic (2n = 41) lines of Triticum aestivum (2n = 6x = 42, AABBDD). The seed sets with the 4 varieties of Triticum aestivum ranged from 0.6 % to 12 %. The average seed set (8 %) in the second backcross was less than the average seed set (11 %) obtained from the first backcross. The percentage of the seed set (10 %) with Chinese Spring disomics was more than double that obtained with the monosomics (4 %). Monosomics 6 B and 3 D were more successful (4 % seed set) than monosomics 1 D and 4 D (2 % seed set). The seed set in the pentaploids (AABBD) varied with the original tetraploid (AABB) parent. An advantage of the general backcross appears to be that it may replace and balance certain disharmonious combinations that occur in aestivum X durum segregants. Since one of the aims of extraction is to analyse the genetic diploidization of allopolyploids, it is important to use only those species and varieties which have been isolated from introgression from related taxa.
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