| I. Research Notes The meiotic behaviour of a triploid Triticum monococcum D. METTIN, R. SCHLEGEL and W.-D. BLUTHNER Martin-Luther-Universitat Halle-Wittenberg, Lehrkollektiv fur Pflanzerzuchtung, 4104 Hohenthurm b. Halle/S., DDR From a large number of reciprocal crosses between a diploid T. monococcum var. macedonicum and the corresponding colchicineinduced autotetraploid strain we obtained a single triploid individual. This plant with 2n=3x=21 chromosomes as expected, was fully normal in appearance, had a somewhat delayed growth and was mainly characterized by an increased tillering capacity. The triploid was completely male sterile (measured by stainability of the pollen), and all attempts to get seed set after backcrossing to the diploid parent failed. It was thus not possible to obtain any offspring, especially primary trisomics. Meiotic preparations were made in order to analyze the pairing behaviour in metaphase I. The data obtained are given in Table 1. In spite of the fact that this particular triploid had three sets of homologous chromosomes the number of trivalents per cell never exceeded three, while most of the cells (about 80%) had either one or two trivalents only (Table 2, see also Fig. 1). There is, in the present material, not only a comparatively low number of trivalents in general, but the kind of association found was always a chain (see Fig. 1). Comparing the numbers of bivalents and univalents per cell or in general the latter have an excess which is mostly three. This behaviour can be attributed either to premature disjunction of the members of a trivalent or to fully asynapsis. Since most of the unpaired chromosomes in cells with a high proportion of univalents were not arranged in end-to-end or side-by-side associations but were scattered at random it is assumed that asynapsis is partially restricted. There is some evidence that the pairing pattern in the triploid is not primarily caused by a reduced chiasma formation. Considering the chiasmata in ring and rod bivalents in the triploid, calculations have shown that the number of chiasmata per ring bivalent is about 2.4 which is within the range of the diploid parent and the tetraploid derivative (Table 3). |