Possibility of 5B-like effect in diploid species

OKAMOTO, M. and N. INOMATA

Abteilung fur Pflanzongenetik fur Strahlen und Umweltforschung 8059 Grunbach 1, West Germany, and Laboratory of Genetics and Plant Breeding, College of Agriculture, University of Osaka Prefecture, Osaka, Japan

At meiosis of haploid plants from diploid species such as einkorn wheat, barley, oat and rye certain numbers of bivalents are usually observed although frequencies may vary according to plants. But in diploid species of the above plants no quardivalents have been found so far unless these diploid species were subjected to radiation treatment.

Nobody has suggested possibility of presence of 5B-like effect in the above species.

If chromosome pairing in pollen mother cells of haploids of the above plants is due to chromosome pairing between homologous segments of chromosomes, which seems to be more or less naturally accepted at the present moment, it is quite natural to expect that quardivalents might also be found in diploid species at meiosis, because four homologous segments are or must be present in diploid species. No quardivalent formation has so far been observed as has been mentioned above.

It is very interesting to suggest that a gene or genes which supress quadrivalent formation at meiosis of the above plants may be present in these diploid species.

In hexaploid species of wheat a gene or genes which suppress homoeologous pairing have already been found on chromosome 5B by OKAMOTO (1957) and RILEY (1958), and a gene or genes have recently been found on chromosome 3D by MELLO-SAMPAYO (1971) to have similar but less effect. MELLO-SAMPAYO also reminded OKAMOTO at the 4th International Wheat Genetics Symposium in Columbia (1973) of such effect in A genomes discovered by DRISCOL (1972).

We might then be able to say more strongly that such a gene or genes which suppress homoeologous pairing may also be effective in diploid species as well.

The things remain to be done is to find out whether such a gene or genes may be found in the original diploid species from which the A, B and D genomes come from.

The first approach to such a problem will be test whether the chromosomes of the Aegilops squarrosa have such effect or not.

The method may be outlined as follows.

(1) Cross synthesized hexaploid species on monosomics of Chinese Spring wheat.
(2) Pick up the monosomic plants.
(3) Cross the monosomic plants by Secale cereale, Ae. sharonensis or whatever species suitable for the test.
(4) Compare pairing conflgulations between the plants with or without the chromosome concerned.

If one of the seven chromosomes of the Ae. squarrosa is found to have the effect of suppressing homoeologous chromosome pairing, it may safely be asserted that Ae. squarrosa carries a gene or genes for suppression of homoeologous chromosome pairing.

The test for presence or absence of such a gene or genes for suppression of homoeologous chromosome pairing in the original species from which the A and B genomes come from may not be so simple as that in Ae. squarrosa. But trials are now being to find out such methods.

It may be worth while to mention that the method similar to that with the chromosomes of Ae. squarrosa may be employed with any addition or substitution lines of common wheat.

(Received December 17, 1973)