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Fishing in mixed gene pools
In discussions of the relative merits of genetic manipulation versus `traditional' breeding, the picture is often presented of the gentle breeder, transferring pollen with a deft stroke of the paintbrush and then waiting for nature to take its course. But actually it is very much harder than that. The range of genetic variation within a species or from readily hybridizable species may be limited. The probability of hybridizing with species carrying desirable traits may be very low because of compatibility barriers and because of cytogenetic differences. This is well illustrated by Beta vulgaris (sugar beet), a relatively `young' crop that still has great potential for improvement. Traits such as stress tolerance and resistance to pests and diseases are available in wild beet species and indeed have been transferred to B. vulgaris by crossbreeding. However, introgression of these wild beet traits into sugar beet is very rare, involving the formation of addition lines and other infrequent cytogenetic events. Further, screening for possible hybrids in beet is difficult while searching for hybrids by classical cytogenetic methods is impossible. Faced with this, Desel et al. (Universities of Kiel and Heilongjiang, pp. 171-181) have proved the worth of molecular hybridization techniques using fluorescently labelled DNA probes with chromosome spreads. Different fluorescent dyes were used to label sequences specific for particular Beta genomes. Thus in any one spread it was possible to determine the genomic origin of a chromosome or chromosome fragment. This is a variant of the FISH (fluorescent in situ hybridization) technique for which the term GISH (genomic...) was coined about 10 years ago. In this paper its application to the small genome (and small chromosomes) of Beta and its use to demonstrate the presence in hybrids of DNA from wild species, correlated with the acquisition of particular traits, are particularly noteworthy. Molecular biology thus provides another tool for the `traditional' breeder.
Professor J.A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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