The Hays Golden population has undergone mass selection strictly for yield for twenty-nine generations. DNA samples were isolated from seedlings of this selected population and the control population. DNA was digested with restriction enzyme SstI and Southern analyses were performed with the pGMR3 soybean ribosomal DNA clone (obtained from Elizabeth Zimmer), which contains the 3' end of the 26S gene, the nontranscribed spacer region and the 5' end of the 18S gene. This probe detects bands of 3.6kb, 1.8kb and a 1.6kb doublet; a size polymorphism is observed for the 3.6kb band, which increases to 3.9kb due to spacer length variation. We have detected a 5.3 kb band. The size of this fragment is consistent with the loss of the SstI restriction site in the external transcribed spacer between the 3.6kb and 1.6kb fragment.

This restriction site polymorphism generating the 5.3kb band was detected in all seedlings randomly sampled from the Hays Golden population that has undergone selection for yield. This specific polymorphism was not detected in seedlings randomly sampled from the control Hays Golden nonselected population. Both the selected and nonselected populations were polymorphic for the 3.6kb and 3.9kb fragments. These results are preliminary since only 11 plants from each of the populations have been assayed at this time. Experiments are in progress to evaluate more plants from generation 29, earlier generations and the control population to identify the origin of this variation and frequency of occurrence.

Torbert R. Rocheford, John C. Osterman and Charles O. Gardner
 
 

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