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