Results and Discussions

Analysis of the meiotic chromosome configurations of F₁ plants shows that mean value of rod bivalents per cell was 0.8 in Norrona and 0.6 in T-13, while in monosomic hybrids CS x T-13 it was higher and equals to about 3 bivalents per cell (Tables 1 and 2). The chromosome pairing in hybrids F₁ was less regular than in their parent plants and associations between chromosomes during meiosis were rather weak, which resulted in premature disjoining of bivalents and increase in number of additional univalents. Taking into account percent of PMC with the normal chromosome configurations at MI in F₁ monosomic hybrids (20^II+1^I) it was found that some chromosomes of variety Norrona and mutant T-13 affected pairing in meiosis. Thus, in monosomic F₁ plants from crosses CS x Norrona chromosomes 4A and 4B decreased pairing, whereas chromosomes 1B and 3D increased it (Table 1). In monosomic F₁ plants from crosses CS x T-13 chromosome 3B significantly decreased pairing, and in monosomic hybrids for chromosomes 5A, 1B and 7B meiosis was more regular as compared with F₁ disomics (Table 2).

The existence of further structural differences between the chromosomes of CS, on one hand, and variety Norrona and mutant T-13, on the other hand, is supported by the data on chromosome configurations and multivalent formations at MI in F₁ plants from crosses of CS monosomics with Norrona and mutant T-13.

The presence of reciprocal translocations between the chromosomes of wheat varieties leads to irregular pairing and hybrids produce quadrivalents and other chromosome associations at MI. With the monosomic hybrids, in which one of the chromosome implicated in the translocation is absent, trivalent configurations appears at meiosis (LAW & Worland 1972). The critical F₁ plants have a trivalents in a number of PMC, while the non-critical plants have a quadrivalent configurations (Morris Sears 1967; LINDE-LAURSEN & LARSEN 1974). The occurrence of at least two trivalents without univalents at MI in the F₁ hybrids is indicative of heterozygosity for chromosomal interchange.