Wheat Precise Genetic Stocks at JIC

Details of the majority of the Wheat Precise Genetic Stocks held by the Germplasm Resources Unit can now be found on our new searchable database system Seedstor

Advice on stock availability and their use is available through Adrian Turner (adrian.turner@jic.ac.uk) of the Crop Genetics Department of the John Innes Centre.

Aneuploid stocks

Wheat has an allopolyploid origin, and the homoeology existing between its three component genomes allows a range of aneuploidy to be tolerated. The late Prof. Ernie Sears began accumulating this aneuploid set in the 1940's, and it now comprises around 220 lines. The set is primarily derived from a single cultivar, 'Chinese Spring', and features the loss of one chromosome (monosomy) or a pair (nullisomy), extra chromosomes (trisomy and tetrasomy) and compensation (nullisomy-tetrasomy) involving all 21 constituent chromosomes. There are also telosomic sets in which the same half of a pair of chromosomes is missing (derived via centromere breakage of univalent chromosomes during meiosis. Because each accession has an aneuploid genotype, it is necessary to screen cytologically at either mitosis and/or meiosis each time they are grown. The transfer of aneuploidy to agronomically adapted cultivars via traditional plant breeding methods permitted its effects to be more easily determined. Similarly, locating genes conferring agronomically important traits became possible, an obvious example being the mlo locus, which provided an effective resistance to powdery mildew for many years. With the advent of molecular marker analysis in the early 1980's, the use of these wheat aneuploids, together with the wheat/alien aneuploids (see section 2), confirmed that homoeology within the Triticeae extended beyond the phenotype to the molecular level. This led to the comparative mapping of wheat and its near relatives, and the construction of a molecular map of wheat. In this latter exercise, the compensating nullisomic-tetrasomic lines and telosomic lines have featured prominently.

A graphical introduction to wheat aneuploid stocks can be found here.

Alien Introductions

Wheat has an allopolyploid origin, and the homoeology existing between its three component genomes allows a range of aneuploidy to be tolerated. Innumerable worldwide research projects spanning more than 60 years has led to the establishment of this set of wheat/alien aneuploids. Because each accession has an aneuploid genotype, it is necessary to screen cytologically at either mitosis and/or meiosis each time they are regenerated. Initially, research workers employed traditional plant breeding methods to add a pair of chromosomes from a close relative (alien) to the wheat complement. The establishment of monosomic series in various wheat cultivars (see the 'Aneuploid' section of WPGS) then facilitated the substitution of this alien pair for a homoeologous pair belonging to the wheat. As this unique collection grew, co-operative studies determined both the induced effects of the aneuploidy, and the chromosomal location of alien genes conferring agronomically important traits such as improved disease resistance or tolerance of abiotic stress. One such example is the 1B.1R translocation so popular in European cultivars in the 1980s and '90s. With the advent of novel molecular marker analysis in the early 1980's, extensive use of these wheat/alien aneuploids confirmed that the homoeology within the Triticeae extended beyond the phenotype to the molecular level.

Intervarietal substitutions

While much of the early work on aneuploidy in wheat was conducted in 'Chinese Spring', many other background varieties have been used. The stocks developed by Colin Law and the late Tony Worland are currently in the process of being prepared for inclusion in the database.

References

Law CN, Snape JW, Worland AJ. (1987). Aneuploidy in wheat and its uses in genetic analysis In: Lupton, F. G. H. (ed.). Wheat Breeding. Its Scientific Basis, 71-127, Chapman and Hall, London and New York.