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There were 11 F1
hydrids in the cross of monosomic 3A (Pb. C591) x Kundan. Out of
these, 8 hybrids were disomics and 3 were monosomics. The disomic
hybrids produced only green seedlings, while the monosomics produced
both green and albino seedlings with an overall albino frequency of
11.7%. The absence of albino seedlings in the F2's of
disomic hybrids suggests that the variety Kundan carries a
chlorophyll synthesis gene allelic to that in variety Pb. C591. The
frequency of albino seedlings (11.7%) in the F2's of
monosomic hybrids was very close to that (12.3%) observed in the
selfed progeny of monosomic 3A, suggesting that variety Kundan
carries a gene for chlorophyll synthesis which is located on
chromosome 3A.
In the cross of monosomic 3A (Pb. C591) x Oligo there were 5 disomic
and 5 monosomic hybrids. All the disomic hybrids produced only green
seedlings, whereas monosomic hybrids segregated for albino seedlings
with a frequency of 4.1%. The absence of albino seedlings in the
F2's of disomic hybrids indicates the presence of a gene
allelic to the gene located on chromosome 3A of variety Pb. C591. The
segregation of albino seedlings in the F2 populations of
monosomic hybrids confirmed this. Based on the frequency of albino
seedlings (nullisomics) in the selfed progeny of monosomic
F1 hybrids involving chromosome 3A the observed albino
frequency (4.1%), that fits in a monogenic ratio of 3 green : 1
albino among the nullisomics (cytologically confirmed), suggested the
involvement of one more gene for chlorophyll synthesis besides the
gene located on chromosome 3A in variety Oligo.
There were only 8 hybrid plants in the cross of monosomic 3A (Pb.
C591) x Rht-8 among which 6 hybrids were disomics and 2 monosomics.
Disomic hybrids of this cross produced only green seedlings
indicating the presence of a chlorophyll synthetic gene allelic to
the gene located on chromosome 3A in variety Pb. C591. However, the
monosomic F1 hybrids segregated for green and albino
seedlings, confirming the presence of an allelic gene in variety
Rht-8. The albino frequency observed in the F2 generation
of monosomic hybrids was 3.0%, fitting a monogenic ratio of 3 green :
1 albino among the nullisomic class. The result suggest that variety
Rht-8 also carries two chlorophyll synthetic genes, one of which is
located on chromosome 3A.
So far ten hexaploid wheat varieties involving old and new ones have
been analysed for the presence of chlorophyll synthetic genes
(Table
2). Of these, Pb.
C591, Kundan and Sel. 111 carry only one gene or gene complex for
chlorophyll synthesis whereas Chinese Spring, T.
sphaerococcum, Mara, Oligo, Rht-8, Kalyansona and Sonalika
have been found to carry two genes each. Interestingly enough, at
least one of two genes is always present on chromosome 3A in all the
varieties analysed so far.
References
Austin RB, Morgan CL and Ford MA (1986) Dry matter yield and
photosynthetic rates of diploid and hexaploid Triticum
species. Ann Bot 57: 847-857.
Singh D and Joshi BC (I979) Chlorophyll synthetic genes(s) in
Triticum aestivum (Var. Pb. C591). Wheat Inf Service 50:
45-46.
Joshi BC, Singh D, Lal B and Ram D (1979) A very high frequency of
nullisomics in selfed monosomic population for chromosome 3A of
Triticum aestivum Pb. C591. Wheat Inf Service 50: 12-13.
Singh D and Joshi BC (1986) Location of genes for chlorophyll
synthesis on specific arms of chromosomes in Triticum
aestivum. Euphytica 35: 523-528.
Singh D (1990) Chlorophyll synthetic genes in Triticum
sphaerococcum. Photosynthetica 24: 502-505.
Singh D (1991) Identification and location of chlorophyll synthetic
genes in a wheat variety Mara. Wheat Inf Service 73: 30-32.
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