ICI Seeds, Inc.
Stock 6 induced double haploidy is random
--Ming T. Chang
An experiment was designed to generate double haploids from Stock 6.
Two inbreds that were derived from Oh43 and Mo17 were crossed and the F1
seeds were used as female stock for this study. These Oh43 and Mo17 derivatives
are homozygous pure inbreds as shown from the isozyme test, and their genetic
constitution is homozygous A b pl c1 r-g Y. These two lines carry
different allelic forms at isozyme loci Mdh1, Mdh2 and Idh2
as shown in Table 1. The pollen source was BC2S2 materials that were derived
from crosses between Stock 6 (A b pl C R-g y) and A B Pl C R-nj
y genetic stock. The F1 was backcrossed to Stock 6 (A b pl C R-g
y) twice, then selfed twice. Seeds from the homozygous ears of A
B Pl C R-nj y were chosen as materials for pollen source. The seeds
are white (due to y1) flint with purple color on the crown and plumule
(due to R-nj). The plants are dark purple on leaves, stalk, tassel
and anther (due to B Pl). The isozyme test showed that the BC2S2
Stock 6 material was still segregating at Adh1 and Pgm2 loci
as shown in the Table, but 90% of the individuals were already fixed at
those loci. Since the Stock 6 carries the Pgd1-22 allele and the
two inbreds carry the Pgd1-11 allele, the isozyme difference can
be used to identify the origin of the haploids. A total of 600 ears or
305,778 seeds were obtained. Among those, 98 double haploids were obtained.
These double haploids were pure lines as examined by isozyme markers and
ear to row field evaluation of their morphological uniformity. The allelic
constitutions of these double haploids is summarized in Table 2. Genetic
linkage distance between Idh2-Mdh2 is 1.1 ± 0.6 (Goodman,
MM et al., Genetics 96:697-710, 1980). Among these 98 double haploid lines,
all showed tight linkage and none were derived from a crossover between
and Mdh2 loci on chromosome 6. It is therefore concluded that Idh2
and Mdh2 are tightly linked. The distributions of allelic frequency
among these double haploids were Mdh1-11 (48%) vs. Mdh1-22
(52%), and Mdh2-11---Idh2-22 (54%) vs.
(46%). This is almost a 1 to 1 ratio due to genetically random assortment
of the chromosomes. It is therefore concluded that Stock 6 induced double
haploidy is a random process.
Table 1. Genetic constitution of allelic forms of isozyme loci of the
male and female materials that were used to generate double haploids.
Table 2. Genetic constitution of allelic forms of the double haploids.
|Double Haploids||Genetic Constitution|
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