Intraspecific chromosome manipulation

Abstract

Whole chromosome manipulation within a crop species is restricted in the main to the hexaploid bread wheat, Triticum aestivum (2 n = 6 x = 42). Directed manipulation within this group is possible because aneuploidy is tolerated, and at least 60 monosomic sets, representative of many of the successful wheats of the world, are available. These permit, after recurrent backcrossing and cytological selection, the substitution of whole chromosomes from one variety into another. Substitution lines have been used to identify chromosomes and genes responsible for varietal differences affecting a range of important agronomic characters, and provide the most efficient method of genetical analysis available in wheat or indeed in any crop species. The length of time taken to develop substitution lines is, however, a weakness of the approach. A method in which monosomic sets are crossed reciprocally overcomes this weakness and permits the identification of significant chromosomal effects in one to two generations. Modifications to the method enable chromosomal effects to be studied in any varietal combination even though monosomic sets are not available in all the varieties being studied. The results obtained by intraspecific chromosome manipulation have been exploited in the development of a high-yielding spring wheat after recombination of a single chromosome substituted into a winter wheat. This example suggests that the methods may have direct applications to plant breeding where large chromosomal effects have been identified. This is particularly relevant where the variation concerned is difficult to assess. These methods also have a major part to play in increasing the understanding of the genetic architecture of wheat. It is also likely that they will have value in transferring useful genes from distantly related varieties.