SUMMARYTwo experiments to investigate the crossabilities of varieties of bread wheat, Triticum aestivum, with Hordeum bulbosum are described. In the first a range of varieties having low and high crossability with rye, Secale cereale, were used.It was found that a strong positive correlation between the crossabilities of wheat varieties with H. bulbosum and with rye exists.In the second experiment the genetics of crossability was investigated using chromosome substitution lines of the non-crossable variety, Hope, into the crossable variety Chinese Spring. Two chromosomes, namely 5A and 5B of Hope, were found to reduce markedly the crossability of Chinese Spring. These chromosomes were those identified by Riley and Chapman (1967) as being responsible for the crossability of Chinese Spring with rye, reinforcing the conclusion that the crossability of wheat with both species is governed, at least in part, by the same genetic system. However, other chromosomes were also shown to affect the crossability of Chinese Spring, although to a much lesser extent. The use of this interspecific cross to produce wheat dihaploid lines for breeding purposes is discussed.

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An attempt to produce a set of addition lines of Aegilops sharonensis to the wheat variety 'Chinese Spring' produced only one addition line. This was due to preferential transmission of one chromosome from Ae. sharonensis. This chromosome was studied in detail by established cytological methods of chromosome observation and by the newer techniques of C-banding and in situ hybridization of a cloned DNA sequence. The chromosome was found to be partially homologous to an Ae. sharonensis chromosome of similar behaviour in another wheat addition line. The incomplete homology of the two Ae. sharonensis chromosomes was due to the presence of a translocated segment of a wheat chromosome. - Substitution lines of the Ae. sharonensis chromosome for wheat homoeologous group 4 were produced and the Ae. sharonensis chromosome thereby designated 4 S (l) .

The main objective of this work is to demonstrate the expression of salt tolerance g,enes in a wheatAgropyron amphiploid. Salt tolerance tests were carried out on wheat varieties, 'Chinese Spring' and 'Glennson 81', the amphiploid between 'Chinese Spring' and A. juncenm, A. junceum and amphiploid X wheat hybrids. Apart from germination in petndishes all other tests were carried out on piants grown in saline hydroculture tanks. Fresh weight measurements are given for stressed and non-stressed plants as well as measurements of harvest ripe plants. The utility of A. junceum as a source of sah tolerance genes for wheat is discussed.

Lines of Triticum aestivum Chinese Spring (2n = 6x = 42) which were ditelocentric or doubly ditelocentric, in turn, for the 14 chromosomes of the A and B genomes were pollinated by Triticum 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 of T. urartu matched 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 14 T. aestivum x T. urartu hybrids was compared with earlier results obtained from hybrids between T. aestivum and T. boeoticum. It was proposed that the higher trivalent frequencies seen in the T. boeoticum hybrids could be due to homoeologous pairing and that the genotype of T. boeoticum has the capacity partly to suppress the activity of the Ph locus of chromosome 5B of wheat, as a result of which homoeologous pairing is normally prevented.