THE GAMETOCIDAL CHROMOSOME INDUCES RECIPROCAL TRANSLOCATIONS IN WHEAT

Laboratory of Plant Genetics Graduate School of Agriculture Kyoto University Sakyo-ku, Kyoto 606-8502 JAPAN

When monosomically introduced into wheat, so-called gametocidal chromosomes of wild species belonging to genus Aegilops, related to wheat genus Triticum, are known to induce chromosomal lethal or sublethal mutations in gametes lacking the Aegilops chromosome. The chromosome mutation involves breakage in chromosomes or chromatids and repair or fusion of the broken ends, resulting in the generation of deletions and translocations. Two such chromosomes derived from Ae. triuncialis which cause sublethal chromosome mutations have been introduced into the barley chromosome 4H addition and rye chromosome 1R substitution lines of common wheat. In the progeny of the lines, disomic for the barley or rye chromosome and monosomic for the Aegilops chromosome, chromosomal structural changes involving the barley or rye chromosome occurred in more than 10% of the plants examined. Some of them had two wheat-alien translocations: one with barley (or rye) centromere and one with a wheat centromere. Sequential C-banding and GISH revealed that the pairs of wheat-alien translocations so far investigated are symmetrical reciprocal translocations; consequently, the two translocation chromosomes formed a trivalent with a wheat chromosome at MI. This genetically induced reciprocal translocations seem to have played a critical role in the karyotypic evolution of wheat and Aegilops. It will be discussed how such translocations are generated at the chromosomal level, leading to gene elimination or duplication in the course of the polyploid evolution of wheat.