New Aneuploids of Common Wheat
Abstract Chromosomal structural changes can be induced by the addition of specific alien chromosomes called 'gametocidal (Gc) chromosomes'. In the monosomic addition of the Gc chromosome to common wheat, chromosomal breaks occur in gametes receiving no Gc chromosome, and the broken ends heal and stabilize in the subsequent generations. Thus, by the so-called Gc system, deficiencies and translocations can be induced in common wheat and also in alien chromosome addition and substitution lines of common wheat. Deficiencies of wheat and alien chromosomes were cytologically identified by the chromosome banding and in situ hybridization techniques. The plants carrying deletions or wheat-alien translocations were established as new aneuploid lines of common wheat with sub-arm aneuploidy. Those for wheat chromosomes are called deletion stocks and those for alien chromosomes are called dissection lines. The new aneuploids have been used for cytological chromosome mapping and have corrected some mistakes in genetic mapping.
Aneuploids of Common Wheat
The hexaploid nature of common wheat (Triticum aestivum L., 2n = 6x = 42) enables us to produce aneuploids rather easily. Almost 60 year ago Sears (1954) first reported the systematic production of aneuploid lines in common wheat. These socalled conventional aneuploids comprise different series of aneuploid lines of Chinese Spring wheat, such as monosomics, nullisomic, nullisomic-tetrasomics and ditelosomics (Sears 1954; Sears and Sears 1978), which have been used extensively for the genetic and genomic studies of wheat. He allowed everybody to use those aneuploids freely. I believe that his generosity stimulated the subsequent development of not only genetic and cytogenetic studies but also molecular and genomics studies of wheat. Common wheat can also tolerate the addition of alien chromosomes from related wild and cultivated species, such as goatgrass, wheatgrass, rye and barley. In some cases, alien chromosomes substitute for wheat chromosomes very well to be established as common wheat cultivars, e.g., those carrying a 1R(1B) substitution.
The new aneuploids described here are not really new, but I would like to distinguish them from the conventional aneuploid lines that have aneuploidy of whole chromosomes or chromosome arms. I would like to define these new aneuploids as 'aneuploids that have sub-arm aneuploidy', which can be induced by two genetic mechanisms, as well as by artificial mutation. By the suppression of the pairing control (ph: pairing homoeologous) gene, homoeologous pairing is induced between wheat and alien chromosomes to generate wheat-alien recombinant chromosomes in alien substitution lines of common wheat. Also, unique chromosomes called gametocidal (Gc) chromosomes, which were introduced from specific wild species of the genus Aegilops, induce chromosomal breakage in common wheat to generate deficient chromosomes and wheat-alien recombinant chromosomes. I named the common wheat lines carrying deficient wheat chromosomes 'deletion stocks' (Endo and Gill 1996), and I proposed to call generically the wheat lines carrying deletions or translocations of alien chromosomes 'dissection' lines (Endo 2007).