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Homoeology of a rye (Secale cereale var. DAKOLD) chromosome1)


Botany Department, The University, Gorakhpur, U.P., India

The substitution of alien chromosomes into the wheat complement is now well established. A number of alien substitution lines having 20 pairs of wheat chromosomes and one pair of alien chromosomes are now known. In these substitution lines the alien chromosome came from Aegilops (RILEY et al. 1966), Agropyron (BAKSHI & SCHLEHUBER 1959, WEINHUES 1960 and KNOTT 1964) and Secale (O'MARA 1947, RILEY 1964 and JENKINS 1966).

With the success of these substitutions, now there is increasing interest in the genetic relationship between substituting alien chromosome and the replaced wheat chromosome. Efforts are also being made to extend the homoeologous relationship between three genomes of wheat to the other genera of the sub-tribe Triticinae viz. Aegilops, Agropyron, Haynaldia and Secale. Some of the alien chromosomes have already been designated on the basis of knowledge regarding their homoeology e.g. 6R for a rye chromosome (RILEY 1964) and 2M for an Aegilops chromosome (RILEY et al. 1966).

Since rye chromosomes do not pair with wheat chromosomes, one has to depend on indirect evidence in order to find out the homoeologous relationships. Compensation effect of a rye chromosome for the absence of different wheat chromosomes can, for instance, be studied in the same manner in which nullisomic-tetrasomics were studied by SEARS (1966). Compensation can either be studied in the form of morphology, meiotic stabiltiy and fertility of the substitution lines (20"W + 1"R) or in the form of transmission of substitution (20'W + 1'R) and normal wheat gametes (21'W) in the form of pollens.

In order to study the compensating effect of rye chromosome I (designated after BIHATTACHARYYA & JENKINS 1960), F1 plants of the constitution 20"W + 1' W + 1'R were obtained. For this purpose wheat monosomics of the D genome were pollinated by the addition line (21"W + 1"R) for rye chromosome I. These F1 lines belonged to 1D to 6D depending upon wheat monosomic from which one was derived. These six F1 lines were then used to pollinate normal wheat plants and the transmission of four types of gametes (20'W, 20'W + 1'R, 21'W and 21'W + 1'R) was studied in the progeny.

Theoretical ratios were, however, obtained following HACKER (1965) and RILEY et al. (1966). There was cytological and genetical evidence that rye univalent was eliminated in 86.4% of the gametes. Wheat univalent was lost in 75% of the gametes as usual. Therefore, when 20'W and 20'W + 1'R gametes did not function due to competition, the transmission of the remaining two types of gametes was expected in 25: 4 ratio. Also when there was no competition between 21'W and 20'W-1'R gametes as a result of compensation, 12 : 25 : 4 ratio was expected.

1) This work was done by the author as a Commonwealth Scholar at the Department of Plant Science, University of Manitoba, Canada
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