| A synthesized common wheat obtained from a triploid
hybrid, Aegilops squarrosa var. strangulata(female) x Triticum
durum(male)1) Tetsuo SASAKUMA and Hitoshi KIHARA Kihara Institute for Biological Research Mutsukawa 3-122-21, Minami-ku, Yokohama, Japan It is known that about 70% of plant species are polyploidy, and many are allopolyploidy. Allopolyploid species might have evolved through following three processes; (i) compatible crossing between two species, (ii) chromosome doubling in the F1 hybrid, and (iii) producing fertile gametes accompanied with stable chromosome pairing among progenies. In Triticinae, fertile F1 hybrids and natural amphiploidization have been reported in the crosses of Secale x Triticum (ROBBELIN & SMUTKUPT 1968), T. dicoccoides x Aegilops ovata (KIHARA 1931), T. dicoccoides x Ae. squarrosa (KIHARA & LILIENFELD 1949), Ae. speltoides x Ae. umbellulata (MITSUOKA 1953), T. persicum x Ae. squarrosa (TABUSHI 1956), T. boeoticum x Ae. squarrosa (SEARS 1941), Ae. heldreichii x T. durum (MAAN & SASAKUMA 1977), and T. aestivum x Agropyron disticum (PIENAAR 1980). These data indicated that the three processes above mentioned were independent events each other and was subjected to genic control as well as environmental one. Most of these amphiploids were obtained only in uni-directional crosses except one involving Ae. heldreichii x T. durum, mainly because of cross-incompatibility in the reciprocal crosses including zygotic lethality. On the other hand, many lines of synthesized 6x wheat with the genome constitution of AABBDD have been produced through spontaneous or colchicin-induced amphiploidizations, and they have been utilized for evolutional and genetical analyses, as well as for breeding programs (KIHARA 1944; MCFADDEN & SEARS 1946; TABUSHI 1956; KERBER & DYCK 1978; MAAN & SASAKUMA 1978). All these synthesized wheats were produced from the crosses of various Emmer wheats (AABB) as female parents with the pollen of Ae. squarrosa (DD), and the reciprocal cross (squarrosa x Emmer) was reported to be of zygotic lethal. A review on cross-compatibility among Triticum and Aegilops indicates that it is controlled by ploidy balance, genic compatibility, or nucleus-cytoplasm interaction between parental species (KIHARA 1937; SEARS 1941; NISHIYAMA 1979; MAAN 1977). Crossincompatibility might be overcome with polyploidization of female parent, chromosomal manipulation, or embryo-culturing. We have obtained lines of synthetic 6x wheat from the crosses involving Ae. squarrosa as female parents, of which breeding processes are described in the present paper. Materials and Methods Ae. squarrosa var. strangulata (2n=14;DD) was used as female parent in the crosses with T. boeoticum (2n=14; AA), T. monococcum (2n=14; AA). Ae. speltoides (2n=14; SS), T. timopheevi (2n=28; AAGG), or Emmer (2n=28; AABB) and Dinkel (2n=42; AABBDD) wheats. Their crossed seed-set, seed plumpness, and germination ability of produced seeds were examined. From the seeds obtained from Ae. squarrosa (male) x T. durum Selection 56-1(female), young embryos were aseptically removed at 14 days after pollination, and placed on the agar media in test tubes each containing 10 ml of RM-64 medium (LINSMAIER & SKOOG 1965) supplemented with 10 mg/l of GA3 and 0.1 mg/l of kinetin. Young embryos were cultured under continuous illumination at 20C until seedlings with roots grew up. The F1 hybrids obtained were grown in pots with soil, and their PMC's and microspores were sampled to provide for cytological observations of microspore development of the interspecific F1 hybrids. Also, chromosome pairing at MI and fertility of their progenies from selfing and crossing were examined. In order to obtain the auto-tetraploid lines, seedlings of 10 accession lines of Ae. squarrosa at tillering stage were treated with 0.2% colchicine in 2% dimethyl sulfoxide (DMSO) solution for 5 hr after leaves and roots of seedlings were cut back to about 5 cm. The treated seedlings were re-potted after washing in running water and grown with sufficient moisture in greenhouse. Their chromosome constitutions were cytologically examined with renewed roots and PMC's. The efficiency of colchicine treatments for obtaining auto-tetraploids were described in the report by SASAKUMA & KIHARA (1981). The autotetraploid lines were crossed with T. durum Sel. 56-1 or T. aestivum cv. Chinese Spring and the chromosome pairing and fertility of F1 hybrids were examined. |
| 1) The present study was conducted as a part of the Cooperative Project on NC-Heterosis Breeding directed by H. Kihara, and financially supported in part by the Grant-in-Aid No. 1445 (1980) of Ministry of Agr. Forest. and Fish. of Japan. |