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Wheat Information
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Number 72: 18-24 (1991)
Ditelosomic
analysis of some morphological characters in wheat, Triticum
aestivum cv. 'Chinese Spring'
Afshan Afzal and Ahsan A. Vahidy
Department of Genetics, University of Karachi, Karachi- 75270,
Pakistan
Introduction
Aneuploidy, which is the loss or increase of chromosomes has been
widely studied in hexaploid wheat, Triticum aestivum (2n = 6x
= 42). Aneuploids can be classified as primary or secondary, the
former being a loss or increase of complete chromosomes, the latter
involve different dosages of chromosomes derived through the
misdivision of the centromere.
Due to the availability of the aneuploid series in 'Chinese Spring',
which was developed by Sears (1954), the complexity of genetic
analysis in hexaploid wheat has been greatly reduced. All the 42
possible telocentrics have been obtained (Sears and Sears 1978). Out
of these, 35 are maintained as ditelosomics. They have been obtained
by selfing either monotelosomics or monotelodisomics (Sears and Sears
1978). Ditelosomics, in which each line is deficient in one pair of
chromosome arms, breed true and are usually of high fertility (Law et
al 1987). These are most frequently used to study the role of
individual chromosomes, as differences for a particular character can
be directly attributed to the effect of the missing arm.
Days to heading, whose nature of dominance is not clear yet, is a
complex character. Date of sowing, day length, latitude and day and
night temperatures are some of the factors affecting days to heading.
Spike length is a genic character. Genes controlling spike length
have an additive effect. Leaf size has a direct relationship with
biomass and yield of the plant. As compared to other leaves, the
flag-leaf makes an important contribution of photosynthates
especially at the stage of grain-filling. Hence elucidation of the
role various chromosomes play in determining flag-leaf size is
important.
In this paper, the contribution of chromosome arms in the performance
of some agronomic characters, viz., days to heading, spike length,
flag-leaf length and width was estimated by comparing ditelosomics
with normal disomics in T. aestivum cv. 'Chinese
Spring'.
Materials and Methods
The material for the present study comprised of 32 ditelosomics,
which could be maintained and confirmed cytologically, and disomics
of T. aestivum cv. 'Chinese Spring'. The seeds of the
ditelosomics were kindly provided by Dr. E. R. Sears, University of
Missouri, Columbia, U.S.A., and maintained at the Department of
Genetics, University of Karachi, Karachi, Pakistan.
The seeds were placed on moist filter papers in Petri dishes and kept
at 20C. Root tips were collected after 3 days for cytological
confirmation. The seeds were resown in small pots and kept at 20C.
After 15 days, the plants were transferred to large pots and kept in
the screen house, i.e. in the open, under natural conditions.
The day on which the spike emerged from the boot leaf was taken as
date of heading from which days to heading was calculated.
Observations on spike length, and flag-leaf length and width were
recorded at maturity. Mean and standard error for these variables in
each line were calculated. The statistical analysis was carried out
using the statistical package SPSS/PC+ and utilizing the command
MANOVA. The analysis of variance was done by using the Completely
Randomized Design (CRD). Several types of contrasts are available for
different types of parameter estimates. The contrast used in our
analysis was 'SIMPLE' in which one variable (in this case the
disomic) was compared to the rest (the ditelosomics). This type of
analysis is not orthogonal (Norusis 1988).
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