| Differential suppression of homoeologous pairing in
two recombinants of Triticum persicum x T. dicoccoides Barbara APOLINARSKA and Adam J. LUKASZEWSKI Institute of Plant Genetics, Polish Academy of Sciences, ul. Strzeszynska 30/36, Poznan, Poland The discovery of the genetic system controlling diploid-like pairing of chromosomes in wheat (OKAMOTO 1957, RILEY and CHAPMAN, 1958) opened new areas to wheat cytogenetics. However, due to lack of allelic variation, some aspects of this system were difficult or even impossible to study. To induce the variation some authors have undertaken mutation studies which resulted either in deletion in chromosome 5B (SEARS 1975) or in a weaker form of homoeologous pairing suppressor (mutant 10/13, RILEY 1973). In this paper we present results indicating that natural variation in the system controlling chromosome pairing may exist in tetraploid wheats. Materials and Methods Two recombinants of tetraploid wheats, Xu and Do, selected for good crossability with rye from Triticum persicum var. rubiginosum x T. dicoccides var. spontaneonigrum hybrid by LAPINSKI (LAPINSKI, LUKASZEWSKI, SODKIEWICZ, APOLINARSKA 1979) were crossed to diploid winter rye Secale cereale commercial variety Dankowskie Zlote. The resulting wheat-rye F1 hybrids were backcrossed to the paternal rye. Out of the BC1 generation 28 chromosome plants, believed to be of ABRR constitution, were selected and their meiotic behaviour was analysed along with ABR F1 clones. All spikes were fixed in absolute ethanol: glacial acetic acid (3:1) and refrigerated. For routine analysis anthers were squashed in 2 % acetoorceine, while for chromosomes banding anthers showing desired stage of development were hydrolysed in 0.2N HCl for 45 min. at room temperature and squashed in a drop of 45 % acetic acid on gelatine-coated slides. The procedure employed thereafter was essentially the same as used in the University of Manitoba, Canada, and described by BENNETT, GUSTAFSON and SMITH (1977). Results and Discussion The results obtained for routine and Giemsa banding analysis of chromosome pairing in MI of meiosis are given in Tables 1 and 2, respectively. Regardless of the variation between years, both in F1 and in BC1 the Xu wheat line derived hybrids showed significantly more chromosomes paired per PMC than the Do derived hybrids. The Giemsa banding allowed the authors to study the frequencies of wheat-wheat, rye-rye and wheat-rye associations in meiosis. In BC1 it was found that not all rye chromosomes formed bivalents, 5II and 6II being the most frequent configurations, 33,3% and 25,5% for Xu hybrids and 29,6% and 38,9% for Do, respectively. The remaining rye chromosomes were present either as univalents or they were involved in wheat-rye associations in which the presence of true chiasmata could not always be precisely determined. The evident secondary associations were not included into the data presented in Table 2. Stronger suppression of homoeologous pairing in Do resulted in more regular pairing of rye chromosomes in BC1 and in reduction of wheat-rye associations, both in F1 and BC1. This indicates that pairing of rye chromosomes was affected by the system of pairing control of wheat, at least to certain extent. |
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