SPECIES-SPECIFIC DNA-SEQUENCES IN THE TRITICEAE

Species specific DNA sequences are desirable markers for studying relationships between species and for plant breeding. This paper describes two aspects of molecular cytogenetic analysis of essentially species specific DNA sequences in the tribe Triticeae: sequences that differ substantially in their abundance and homology between species or genomes. Firstly, total genomic DNA can be used as a probe which is made highly specific to species by blocking with DNA sequences common with other species. Examples are given from studies of intergeneric and interspecific hybrids: Hordeum chilense x Secale africanum and H. vulgare x H. bulbosum. Secondly, species specific probes can be obtained from isolated and cloned DNA sequences. Both in situ and Southern hybridization techniques have proven important; in situ hybridization is required for localization and finding the distribution of sequences in the genome while Southern hybridization gives information about the nature and structural variants of sequences. The understanding of sequence behaviour, evolutionary patterns and organization in the genome may lead to more effective and directed production of new recombinant lines, wide hybrids, or alien gene transfer.