Documenting Intraspecfic Genome Size Variation in Soybean

Reports of genome size variation in soybean [Glycine max (L.) Merr.] have ranged from 40 to 0%. This wide range has resulted in doubts of the existence of intraspecific DNA variation in soybean. Eighteen soybean lines were analyzed by flow cytometry to determine their genome size. The lines were selected on the basis of diversity of origin. Intraspecific genome size variation was observed at approximately 4%. To ensure that the variation observed was reproducible and not due to technique error, the two highest and lowest genomes size accessions were reanalyzed. The order and variation observed between the high and low genome size accessions were maintained. To ensure further that the differences were reproducible, seeds from the two highest and lowest genome size accessions were planted in different locations in the USA, grown to maturity, harvested, and the seeds returned to Illinois. The harvested seed was analyzed and again the order and variation in genome size between the high and low genome size accessions were similar to the previous two analyses even though more than 1 yr had passed between the analysis. In addition, two experiments using Amaranthus palmeri S. Wats as an internal standard were conducted. In both of these experiments, the observed variation between the previously reported high and low genome size soybean lines was approximately 1 to 2%. The variation between the high and low genome size soybean lines is reproducible. The variation reported here indicates that the DNA amount variation is between I and 4%, lower than was originally reported.