Plant Genome II Conference
Town & Country Conference Center, San Diego, CA, January, 1994.
PG-II: USING RECOMBINANT INBRED LINES OF SOYBEAN TO ASSESS THE EFFECTS
OF INTERACTING (EPISTATIC) QUANTITATIVE TRAIT LOCI
USING RECOMBINANT INBRED LINES OF SOYBEAN TO ASSESS THE EFFECTS
OF INTERACTING (EPISTATIC) QUANTITATIVE TRAIT LOCI
Karl G. Lark and Levi Mansur, Department of Biology, University
of Utah, Salt Lake City, UT 84112; James Orf, Department of
Agronomy and Plant Genetics, University of Minnesota, St. Paul,
MN 55108
A population of 250 recombinant inbred lines (RIL of soybean
have been extensively characterized for various agronomic traits
including height, lodging, seed oil, seed protein, seed weight,
maturity and yield. A large amount of transgressive variation
was observed for all of these trait phenotypes, indicating that
the parental genotypes are quite different. About 200 of these
lines also have been genetically characterized with RFLP markers
-- comprising 1700 cm of linkage (26 linkage groups) as well as
about 20 unlinked markers. Quantitative trait loci have been
located by regression onto alleles at individual loci. In
addition, interactive QTL have been located by pairwise
comparison of loci in plants with extreme phenotypes. The model
traits, height, lodging and height/lodging (the ability of tall
plants to stand upright), are explored in depth. Alleles at
pairs of loci were compared in plants with extreme phenotypes and
combinations suggesting allelic interactions were analyzed in
detail. Fifteen single locus QTL were found for these three
traits, associated with 11 linkage groups as well as one unlinked
marker. In contrast, more than 20 pairs of interacting QTL were
found for these same three traits. These interacting QTL were
associated with 23 linkage groups as well as two unlinked
markers. Of these pairs only 5 involved loci which had been
detected by regressing onto alleles at single loci. That is,
individual loci involved in the remaining more than 15
interactions did not, by themselves, affect these traits. The
effect of interacting pairs of QTL on trait variation varied from
a few percent to very large effects - e.g. one QTL by itself had
no effect on height, but as a result of its interaction with
other loci it controlled 25% of the variation in height (i.e. 25
cm out of a total of 100 cm of genetic variation). In addition,
it was found that in conjunction, several interacting loci could
control a large fraction of the genetic variation. Implications
for plant breeding and for the evolution of naturally inbreeding
plants will be discussed.
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