Equivalence of the A genome of bread wheat and that ofTriticum urartu

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Abstract
SUMMARY: Lines ofTriticum aestivumChinese Spring (2n= 6x= 42) which were ditelocentric or doubly ditelocentric, in turn, for the 14 chromosomes of the A and B genomes were pollinated byTriticum urartu(2n= 14). The behaviour of the marked telocentric chromosomes was scored in the 14 distinct hybrids obtained from these pollinations. In 6 of the hybrids in which different A genome chromosomes were marked by telocentrics there were from 50 to 80% of the pollen mother cells in which the telocentrics were paired. In the seven hybrids in which different B genome chromosomes were marked the telocentrics were never paired. It was concluded that the genome ofT. urartumatched very closely the A genome of hexaploid wheat and that it did not correspond, as had been proposed by Johnson, to the B genome. The pairing behaviour of the 14T. aestivum×T. urartuhybrids was compared with earlier results obtained from hybrids betweenT. aestivumandT. boeoticum. It was proposed that the higher trivalent frequencies seen in theT. boeoticumhybrids could be due to homoeologous pairing and that the genotype ofT. boeoticumhas the capacity partly to suppress the activity of thePhlocus of chromosome 5B of wheat, as a result of which homoeologous pairing is normally prevented.