Identification of the chromosomes of the A and B genomes

M. OKAMOTO

Curtis Hall, University of Missouri, Columbia, Missouri, U.S.A.

On the basis of genetic analysis of stem solidness, Larson (1953) suggested that chromosomes II, III, IV, V, VI, VII, and XIV of the Chinese Spring variety of T. aestivum belong to the A genome. Her distribution lacks cytological evidehce, however, except that Matsumura (1952) places the chromosome missing in B type speltoids (chromosome IX) in the B genome.

In order to obtain critical cytological evidence as to which chromosomes belong to the A genome and which to the B, crosses were made of plants carrying one or a pair of telocentric chromosomes of the A and B genomes with AADD plants (amphidiploid T. aegilopoides x Ae. squarrosa). It was expected that a heteromorphic bivalent would be found at meiosis of the F₁ 35-chromosome plants if the chromosome belonged to the A genome, while it would not be observed if the chromosome belonged to the B genome.

The results thus far obtained suggest that chromosomes V, VI, IX, and XI are in the A genome, and I,VII, and VIII in the B genome. The results are in agreement with Larson's hypothesis, ,except that chromosome VII and XI are reversed and IX is here indicated to belong to the A genome. Since chromosomes V and IX are in the same homoeologous group, it seems unlikely that both belong to the same genome. Experiments are under way which it is hoped will shed further light on this problem.

Chromosomes III, X, and XII will be tested in the spring of 1957.

(Received March 26, 1957)