Checking for possible contaminants among new mutants

We have been surveying mutants resulting from EMS mutagenesis, with special attention being paid to those of possible interest to maize breeders. Some have stood out as exceptional (e.g., Wlf*-1726 has a short plant and short, wide leaves which are dark green; lgp*-2086 is larger in several dimensions, a little earlier and stays green longer). Some families have segregated for three or more out of a considerable list of divergent traits (tillering, earliness, husk flags, many kernel rows, many tassel branches, pale kernels often with larger dents). Some of these families look like they might be contaminations because of the many segregants, some of them possibly linked, so an initial test for purity of pedigree has been run using isozyme electrophoresis.

Four families with possible contamination (set 0, four thought not to be contaminated (set B), and five checks (set A) were sent to Stephen Smith at Pioneer Hi-Bred International, Inc., to be analyzed by electrophoresis. The test materials resulted from fertilization of inbred line A632 by EMS-treated pollen of inbred line Mo17, selfing of the M1, and, in most cases, outcrossing to Mo17. Set C contained families segregating (1) erl*-2077 (early by 6 days, also tillered, thick cob); (2) lgp*-2087 (large plant, also many kernel rows-usually 17); (3) Wlf*-1726 (above); and (4) mbr*-2088 (many tassel branches, also tillering, earliness, husk flags, many kernel rows, pale kernels). Set B had (1) Erl*-2102 (early by 3-5 days, also small plant); (2) erl*-1729 (early, also short plant); (3) shp*-1749 (short plant); (4) lgp*-2086 (above).

There were 21 isozyme loci included in the assay representing most of those normally studied at Pioneer and elsewhere. Twelve plants were examined for each test family, and eleven for each check. Set B proved to have only the allozymes of the parents. Set C was mixed; the family with mbr*-2088, the most likely to be contaminated, showed deviation from parental norms for seven isozyme loci involving all plants. The erl*-2077 family had one plant with a deviant allozyme band. The lgp3*-2087 family had deviant allozymes or gave obscure bands for five isozyme loci involving all plants, and there was difficulty in reading two of the same isozymes for Wlf*-1726. The Mo17 backcrosses in sets A and B showed the expected predominance of Mo17 allozymes. However, there was a problem with one check, the bulk of ten untreated F2 families. All plants had three or more of the deviant allozymes or difficulties were seen in the scoring of lgp*-2087 and Wlf*-1726 families. Why, we do not know. None of the deviations in the test families matched the allozymes which separate inbred line Mo20 from inbred lines A632 and Mo17, eliminating that stock as a source of contamination.

Until we know more we can only state that mbr*-2088 can be considered a contaminant and that all of set B seems uncontaminated. Remember that occasional allozyme variants might be due to mutagenesis.

Robert McK. Bird, Stephen Smith1 and M.G. Neuffer

1Pioneer HiBred International, Inc.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

Return to the MNL 60 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page