Chromosome conjugation on the hybrids between induced autotetraploid Aegilops squarrosa and Triticum Timopheevi

Abstract

F₁ hybrids between Triticum Timopheevi (AAGG, 2n=28) and induced autotetraploid Aegilops squarrosa (DDDD, 2n=28) have been studied cytogenetically.
Among the 6 F₁ plants obtained, 5 are observed to have 2n=28 chromosomes (AGDD) in PMC's as expected, while the remaining one has 2n=29 (AGDD+1).
The chromosome conjugations and their frequencies at the first metaphase of PMC's are shown in Table 1 for the F₁ plants having 28 chromosomes and in Table 4 for that having 29. Namely, 0-1_Iv+0-2_III+5-10_II+8-16_I and 0- 1_IV+0-2_III+4-9_II+10-17_I are observed, respectively. The average values of chromosomes conjugations per cell are 0.0016_IV+0.0428_III+ 7.2476_II+13.37_I for F₁'s having 2n=28 and 0.004_IV+0.466_III+6.692_II+14.202_I for F₁ having 29 (Table 2).
Among the maximum conjugations observed, 10_II, 7 bivalents might have been formed by the autosyndesis between the chromosomes of induced autotetraploid Ae. squarrosa, and therefore the remaining 3 must have been produced by the autosyndesis of A and G genomes of T. Timopheevi on the basis of the partial homology of the chromosomes. The index of chromosome syndesis (Haga 1940) for the hybrids has been calculated by using the frequency of chromosome pairing except the D-D conjugation, 7_II, namely the autosyndesis between A and G genomes, and the index varies from 3.86% to 5.83% with the individual, and 4.71% on the average (Table 2). The index is higher than that of the syndesis between A and B genomes of Emmer wheat (Kihara 1936, Kondo and Kamanoi 1958) and slightly higher than that of the autosyndesis between the chromosomes of A and G genomes in T. Timopheevi haploid plant (Riley and Chapman 1957), as shown in Table 4. It appears that the difference in the indices of syndesis for A-B and A-G genome chromosomes is due to the distinction between the B and G genomes.
Multivalent formations occur at the meiosis of these F₁'s (Tables 1 and 2), and the trivalents are produced by the pairing of the D-D conjugation of the induced autotetraploid Ae. squarrosa with either or both of the genomes of T. Timopheevi, and the tetravalents by the pairing of the said D-D conjugation with the A-G conjugation of T. Timopheevi.
The F₁ plant with 2n=29 chromosomes has only one more chromosome of D genome than the eu-F₁ plants, and this seems to be due to the formation of the gamete of DD+1 in the autotetraploid Ae. squarrosa.