Soybean, Glycine max L. Merr, is used worldwide as an important source
of protein and oil for a wide spectrum of edible~ feed and industrial purposes.
Modem cultivars are derived from relatively few plant introductions (PIs) which
severely limits diversity in soybean germplasm. The United States Department
of Agriculture (USDA) maintains the soybean germplasm collection.
Mitochondrial DNA sequences have been used as markers of diversity at the
cytoplasmic level.
This project included three objectives. The first was a classification of
the 208 varieties of the USDA's 'old domestic collection' of soybean varieties
with two mitochondrial restriction fragment length polymorphisms (RFLP)
markers. Molecular techniques were used to search for additional sources of
cytoplasmic diversity available to soybean breeders. The two polymorphic
markers were, a 2.3 kb HindIII fragment isolated from 'Williams 82'
mitochondrial DNA, and a portion of the mitochondrial atp6 gene. These
markers were used to distinguish cytoplasmic groups based on hybridization
analysis of HindIII-digested soybean DNA Four major groups were observed
with the 2.3 kb marker in the old domestic collection, and several minor
subgroups were also detected.
The second objective included subcloning and sequencing the 0.9 kb and
1.7 kb HindIII-PstI clones flanking the 2.3 kb HindIII fragment from 'Williams
82' DNA The total 4.9 kb PstI sequence from 'Williams 82' mitochondrial
DNA was used to search a sequence database for any homology to known
mitochondrial sequences.
The third objective compared restriction maps of the four cytoplasmic
types in the regions containing homology to the 4.9 kb PstI fragment. DNAs
from the four cytoplasmic types were digested with five enzymes and four
specific clones (0.9 kb PstI-HindIII, 0.8 kb HindIII-XbaI, 1.5 kb Xbal-HindIII,
1.7 kb HindIII-PstI) were used as hybridization probes in Southern analysis to
examine RFLP patterns and construct comparative restriction maps of the four
cytoplasmic types of DNA.
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