Allelism tests of somaclonal variants

--Brent Zehr, David Duncan and Jack Widholm

As previously reported (Can. J. Bot. 65:491-499), we have regenerated plants from callus cultures of several inbreds including an experimental inbred line (EXL-1) and examined their progeny (R1 generation) for somaclonal variation. From 75 R1 EXL-1 families, one white cob, 18 male sterile, three dwarf, one brown midrib, four narrow leaf, one dark green, two "miniature", two albino, one viviparous, one indeterminant growth and five striated leaf somaclonal (SC) mutants were found. These are all nuclear, single gene recessive mutations.

Since similar mutations have been previously described, we carried out allelism tests with known genetic stocks from the Maize Genetics Cooperation Stock Center and the viable R1 families that proved to be homozygous in the R2 generation or R1 families maintainable only in a heterozygous state. In summary, the SC viviparous mutant is allelic with vp1, the SC crinkled leaf mutant is allelic with cr1, the SC indeterminant growth mutant is allelic with id1, the SC white cob mutant is allelic with P1, and one of the SC dwarf mutants is allelic with br1. Another SC dwarf mutant was found not to be allelic with br1, br2, na1, or na2. Also, the SC brown midrib mutant does not appear to be allelic with any of the known brown midrib alleles (bm1, bm2, bm3, bm4). Additional work is being conducted to further characterize the latter two mutants as well as other mutants as yet not analyzed.

While the mechanism causing somaclonal variation is unknown and may be due to several phenomena, any change which would inactivate a gene such as an insertion, deletion, base change or rearrangement could lead to the recessive phenotypes described here. Thus, although the phenotypic mutations generated through somaclonal variation may not be unique, the molecular basis for these mutations may be unique and useful for studies of gene expression and regulation.

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

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