| Hybrid dysgenesis in wheat: its determinants and utilization
for wheat genetics and breeding HISASHI TSUJIMOTO Kihara Institute for Biological Research, Yokohama City University, Mutsukawa 3-122-20, Minami-ku, Yokohama 232, Japan Many abnormal phoenomena, e.g., gametic abortion, chromosome breakage, mutation, embryo and endosperm degeneration, and segregation distortion, appear in wheat lines carrying gametocidal genes of Aegilops or Agropyron species. This syndrome induced by the gametocidal genes is called "hybrid dysgenesis" (TSUJIMOTO & TSUNEWAKI 1985a). I report here the determinants of hybrid dysgenesis and its utilization for wheat genetics and breeding. The gametocidal genes of two strains of Ae. speltoides were introduced into chromosome 2B of common wheat cultivar Chinese Spring (CS) (TSUJIMOTO & TSUNEWAKI 1984; TSUJIMOTO 1986a) and those of some other species are carried on their chromosomes which are added to CS genomes (Table 1). All genes except Gc-Ag1 cause gametic abortion in both male and female sides when they exist in CS background in hetero- or hemizygous (monosomic addition) condition. Gc-Ag1 causes abortion of female gametes only (KIBIRGE-SEBUNYA & KNOTT 1983). Many Japanese common wheat cultivars have a suppressor, Igc1, against the activity of Gc-C, thus, Gc-C does not cause gametic abortion in the background of such cultivars (TSUJIMOTO & TSUNEWAKI 1985b). The gametocidal genes of Sitopsis species of Aegilops, i.e., Gc1s, Gc1b and Gc-S11 cause hybrid dysgenesis in the progeny of CS carrying them, whereas Gc-C causes it, excpet gametic abortion, in cooperation with Igc1 or a linked gene with it (TSUJIMOTO & TSUNEWAKI 1985b; TSUJIMOTO 1986b). Additionally, the actions of Gc-C is completely independent of those of Sitopsis gametocidal genes although Sitopsis gametocidal genes interact each other (TSUJIMOTO & TSUNEWAKI 1985c). Consequently, I propose to divide the hybrid dysgenesis in wheat into two types; one-gene system hybrid dysgenesis for the abnormalities caused by the Sitopsis gametocidal genes, and two-genes system for those by Gc-C and Igc1. No detailed studies have been made on the gametocidal genes of Agropyron species and Gc-S12. Chromosome breakage and translocations caused by the two-genes system hybrid dysgenesis are useful to produce chromosome deletion or translocation lines effectively because production of genetically stable lines without gametocidal gene (Gc-C) is possible by the action of Igc1. Additionally, this system is available for alien gene transfer to wheat genomes without irradiation or skillful cytological technique. |
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