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Materials and methods
A common wheat line carrying a putative third Ms gene
producing dominantly inherited male sterility was received from
Professor C.F. Konzak, Washington State University, Pullman,
Washington, USA. Several aneuploid stocks of Chinese Spring wheat
(CS) were used (Sears 1954, 1963). These included nullisomic 4D-
tetrasomic 4A (nulli 4D-tetra 4A) and nulli 5A-tetra 5D,
double-ditelosomic 4D (dDt 4D; 2n=44; 20+2t"), and dDt 5A that were
originally received from E.R. Sears, University of Missouri,
Columbia, Missouri, USA and were available from a previous study
(Maan et Al. 1987). The euploid CS was used as a control in some- of
the crosses.
The male-sterile plants can be crossed only as female and, therefore,
the Ms genes can not be tested for allelism by conventional
methods involving reciprocal crosses between wheat lines with
Ms genes from different sources. Therefore, a modified
monosomic analysis (Maan et al. 1987) involving the chromosomal
location, chromosome arm location and gene-centromere distance was
used to determine the relationship of the putative third Ms
gene to those in the short-arms of chromosomes 5A and 4D (Maan et al.
1987; Liu and Deng 1986a, b; Deng and Huang 1988).
First, the progenies from a series of four crosses involving a
euploid male-sterile plant with the putative new Ms gene were
examined along with aneuploids of chromosomes 5A and SD to determine
if the new Ms gene was located on chromosome 5A; (a) a
male-Sterile plant carrying a Msms gene pair was crossed to
dDt 5A, (b) a resulting male-sterile F1 (dMt 5A; 2n=43; 20"+t1t'''
5A) to nulli 5A-tetra 5D, (c) a resulting male-sterile segregant with
19"+1'''5D+2t'5A to CS. and (d) a resulting male-sterile plant with
20"+t1t''' 5A to CS, (Table 1).
Second, the progenies from crosses involving an euploid Msms
male-sterile plant and aneuploids of chromosomes 4A and 4D were
examined to determine -if the putative third Ms gene was
located in chromosome 4D; (a) a male-sterile plant carrying a
Msms gene pair was crossed to nulli 4D-tetra 4A and (b) a
trisomic 4A-monosomic 4D male-sterile F1 (20"+1'''4A
+1'4D) to dDt 4D (Table 2).
Third, the cytologically identified male-sterile plants of specific
chromosomal constitutions from above progenies were crossed to CS;
(c) a plant with 20"+t1t'''4D carrying Ms on whole chromosome
4D was crossed to CS; (d) a plant (from a above) with 20+ t1" 4DL
carrying Ms on whole chromosome 4D was crossed to CS; and (e)
a plant with 20"+t1t''' 4D but carrying Ms in telocentric 4DS
was crossed to CS (Table 2). The purpose of
these crosses was to locate the Ms gene to a specific arm of
chromosome 4D and determine its linkage to the centromere.
The experimental plants were grown in a greenhouse in Fargo, North
Dakota. One or more spikes of the segregants were examined for anther
extrusion and seed set in the bagged spikes, and meiotic chromosome
number and pairing was evaluated in the pollen mother cells (PMC's)
at the metaphase I of meiosis. The plants were assigned idealized
chromosomal constitutions according to the maximum observed meiotic
pairing involving chromosomes being tested for the presence or
absence of the Ms gene as described by Maan et a1. (1987). The
Chi-square test was used to compare the probability of fit between
the observed and expected ratios of the fertile and sterile
segregants in the hybrid progenies.
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