| The use of ph mutant increasing homoeologous pairing
in wheat x rye hybrids T.M. SHNAIDER and O.J. PRIILINN Department of Plant Genetics, Institute of Experimental Biology Academy of Sciences, Estonian S.S.R., Tallinn, U.S.S.R. The pairing of homoeologous chromosomes in common wheat, Triticum aestivum L. em. Thell. (AABBDD, 2n=6x=42), is prevented by the activity of suppressor gene located on the long arm of chromosome 5B (OKAMOTO 1957 ; SEARS & OKAMOTO 1958 ; RILEY and CHAPMAN 1958 ; RILEY 1960). In the absence of this gene, named by symbol Ph-pairing homoeologous (WALL et al. 1971), the homoeologues of the A, B and D genomes pair with each other and also with their homoeologues from related species and genera. The induction of homoeologous pairing by the removal of chromosome 5B or the suppression of its effect afford a possibility of transferring genetic material from alien species to wheat chromosome. Induced pairing and crossing-over of an alien chromosome with one of its wheat homoeologues would seem to offer an excellent chance of accomplishing of an alien segment for a closely related wheat chromosome segment (SEARS 1973). To induce alien chromosomes to pair with their wheat homoeologues, it is only necessary to delete chromosome 5B using mono-5B, nullisomic-5B-tetrasomic-5D or, better, a mutant line ph 1 (SEARS 1977, 1980) evidently deficient for the pairing suppressor ph 1. In this paper we present analysis of meiosis in F1 hybrids between common wheat and cultivated rye using mutant ph 1. Materials and Methods The ph 1 mutant Triticum aestivum L. em. Thell. cv. Chinese Spring (kindly provided to us by Dr. O. MAYSTRENKO from Institute of Cytology and Genetics, Academy of Sciences, U. S.S.R., Novosibirsk) was crossed as a female with a diploid self-fertile line of rye, Secale cereale, Kc-517/8 and with diploid rye cv. Pamirskaya. Hybrids between euploid Chinese Spring (CS) and diploid rye cv. Pamirskaya served as control. The spikes of F1 hybrids were fixed in Newcomer's fluid. Meiotic observations were made on PMCs from anthers stained in 2 per cent acetocarmine using squash technique. Results and Discussions Cytological analysis of meiosis in F1 plants revealed a great difference in meiotic behaviour between the hybrid combinations. The control cross (CS x Pamirskaya) showed practically no pairing among the 28 chromosomes. In this hybrid the asyndetic type of meiosis was observed with an occurence of more than 90 per cent of PMCs With 28 univalents at MI and rare rod bivalents. The mean numbers of bivalents and univalents per cell in this hybrid were 0.5 and 27.1, respectively. This kind of asyndetic meiosis was described at MI of meiosis in wheat x rye hybrids by many authors. |
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