ST. PAUL, MINNESOTA

University of Minnesota

 Partial concordance in inbred B37 --D.A. Muenchrath and R.L. Phillips
 
  Concordance or nonconcordance of primordial germline cells in mature maize kernels is an especially important aspect of development that has implications in mutagenesis. With concordance, there is an equal probability that both the male and female gametes produced by a plant derived from a mutagen-treated kernel would carry the same mutation; if gametes with the same mutation unite, the resulting zygote would be homozygous for the mutation. Concordance would permit the expression of recessive mutations in the M2 generation, the first selfed generation following mutagen treatment. Recessive mutations would not be apparent until the M3 generation if the germline cells are nonconcordant. Although maize is assumed to be nonconcordant, concordance may vary with the genotype, environment, or both.

Whole mature kernels of an inbred line, B37, were treated with 25 mM ethyl methanesulfonate (EMS) for 8 hours. The treated kernels were grown to maturity and self-pollinated. A sample of kernels from 200 of the resulting M2 ears was planted ear-to-row and scored for visible mutant phenotypes.

Approximately 11% of the 200 rows exhibited a mutant seedling or plant phenotype, with chlorophyll variants the most prevalent type. Twenty rows segregated 3:1, and one row segregated 1:1, normal to mutant phenotype, indicating primarily recessive inheritance.

Up to four ears were obtained upon self-pollinating plants in each of the 200 M2 rows. Among the resulting M3 ears, 10% segregated for mutant kernel phenotypes. The frequency of variant kernels on each of these ears was 25%, indicative of recessive inheritance.

Kernels were randomly selected from M3 ears produced in the M2 rows segregating for a mutant phenotype to obtain M3 plants. Ears from both normal and variant M2 plants were sampled and the kernels planted ear-to-row. Approximately half of the M3 rows did not show any mutant phenotype, suggesting the kernels sampled did not carry the mutation, or the variant phenotype was not heritable. Several variant phenotypes not observed in the M2 row were expressed in the M3 generation. Among the rows exhibiting a mutant phenotype, the segregation pattern was consistent with recessive inheritance.

Mutations expressed in M2 plants were expected to be dominant under the assumption of nonconcordance. Dominant mutations among EMS-treatment derived lines are known to be rare. The prevalent segregation ratio of 3 normal:1 mutant indicates these apparent mutants are likely to be recessives. The expression of recessive mutants in the M2 generation, together with the appearance of additional recessive mutants in the M3 generation, argue for partial concordance in the mature kernels of inbred B37.

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

Return to the MNL 64 On-Line Index
Return to the Maize Newsletter Index
Return to the MaizeGDB Homepage