| The origin and the evolution of wild tetraploid wheats1)
Masatake TANAKA, Taihachi KAWAHARA and Jun'ichi SANO Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Kyoto, Japan It is the widely accepted theory that A genome parent of the Emmer group (AABB) and the Timopheevi group (AAGG) of the tetraploid wheats is Triticum boeoticum Boiss. (AA). Regarding to the other genomes (B and G), a number of workers suggested Aegilops speltoides Tausch. (SS) as the donor of the B genome to the Emmer (JENKINS 1929, PATHAK 1940, SARKER and STEBBINS 1956, RILEY et al.1958), though there was little evidences that the S genome is homologous to the B genome. The artificial amphidiploid SSAA has been thought to give genomically dissimilar and sterile hybrids with the Emmer wheats. On the other hand, some workers suggested that Ae. speltoides is the donor of the G genome to T. timopheevi Zhuk. (SHANDS and KIMBER 1973). In 1966, the senior author has obtained the amphidiploid SSAA from the cross between Ae.speltoides and T. boeoticum. Data on average chromosome association and seed fertility of the amphidiploid SSAA having 28 chromosomes at F4, F8 and F12 generations are summarized in Table 1. As shown in Table 1, the chromosome association of the amphidiploid SSAA was very low at the F4 and F8 generations indicating cytologically unstable with a large number of univalent formation. The cells with 14 bivalents could not entirely be found. However, at the F12 generation after synthesis, it was found that the chromosome association was rather high with the increase of polyvalents but the decrease of univalent formation. This might indicate the possibility of occurrence of some chromosomal and/or genic changes in this unstable amphidiploid at the recent generations. The F1 hybrids of synthesized SSAA at earlier generations crossed with the Emmer or the Timopheevi wheats did not show close chromosomal homology and they were highly sterile (TANAKA unpublished). However, in 1976, crosses between SSAA at the F11 generation and T. dicoccum Schubl, or T. araraticum Jakubz. were made and two F1 hybrid combinations were examined cytologically as shown in Table 2. Those hybrids showed rather high chromosome association with a few univalents. Furthermore, one hybrid plant produced two viable seeds though seed fertility of the bagged spikes was very low (0.21%). Two F2 hybrid plants were also examined cytologically. Among them, one plant with 28 chromosomes showed higher chromosome association than F1 plants and seed fertility of the bagged spikes increased to some extent (Table 2). This may indicate the occurrence of genetic changes that were tending toward close genetic constitution to that of the Emmer wheats during the progression of generations in the synthesized SSAA. Although all F1 plants set no seed in the hybrid between SSAA and T. araraticum, it may also be assumed that the similar occurrence of the genetic constitution which will be closer to the Timopheevi wheats might be expected during the advance of generations in the synthesized SSAA. |
| 1) Contribution No. 13 from the Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University |
| --> Next |