Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 83pg1
SEEDLING GENOTYPE IDENTIFICATION OF SEED SPECIFIC RECESSIVE
GENES IN SEGREGATING POPULATIONS
Srinavas R. Kata, Brian H. Taylor, A.J. Bockholt and J.D. Smith,
Departments of Soil & Crop Sciences and Biology, Texas A&M
University, College Station, TX 77843
The transfer of specific genes into established inbred lines
by backcrossing is a commonly used breeding procedure. However,
if the gene(s) of interest is recessive and expressed only in
seeds, conventional backcross procedures are remarkably
inefficient. Transcription of a-zein genes is repressed when the
opaque-2 (o2) allele is homozygous, which increases nutritional
quality of the grain. The most rapid conventional method for
converting a standard inbred to an o2/o2 form requires at least 7
generations: initial cross, 5 backcrosses without testcross
identification of o2 and a selfing generation to establish o2/o2
lines. Large populatioin size is required since less than 1% of
the selections made during the conversion will be o2/o2 in the
seventh generation. Population size can be reduced by
alternating backcross and testcross generations, but this would
add 3-4 generations to the conversion time. The use of molecular
markers to identify heterozygous plants prior to selection would
greatly increase the efficiency of continual backcrossing without
testcrosses. Population size could be reduced to a few plants
per generation, and about 25% of the seventh generation seed of
each selection would be o2/o2. We used an O2 derived clone to
identify RFLPs adjacent to the O2 gene that differentiate O2 and
o2 alleles. Under laboratory conditions, these markers
accurately differentiated O2/O2, O2/o2, and o2/o2 genotypes of
juvenile leaf tissue from plants of known genotypes. Field tests
involving F2 and backcross populations were conducted in 1992.
These studies indicate that the procedure is essentially 100%
accurate for determination of seedling genotypes under field
conditions.
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