Iowa State University
University of Missouri

Two independent mutants designated as shrunken6 (sh6) are allelic
--Philip S. Stinard, Patrick Schnable and M. G. Neuffer

In two reports in the 1992 MNL, one from Ames (MNL66:4) and one from Columbia (MNL66:39), we independently reported new recessive mutants on 7S, both with shrunken-opaque kernel phenotype and both giving rise to pale green seedlings. We exchanged stocks of our mutants, and conducted allelism tests in our summer nurseries. (The Ames tests were performed in the nursery of Patrick Schnable.)

In Ames, kernels from the outcross to standard of heterozygous sh6-8601 (the ISU allele) plants were sown in the field and grown to maturity. The second ears of these plants were self-pollinated, and the first ears were pollinated by plants grown from wildtype kernels of selfed segregating ears of sh6-1295 (the UMC allele). The latter plants were also self-pollinated. In each instance in which the self-pollinated ears on both plants segregated for mutant kernels, the ears from the allele test cross also segregated for mutant kernels, confirming the allelism of these two mutants. Seedling tests of mutant kernels from the allele test crosses also gave back the mutant pale green seedling phenotype. Allele tests conducted in Columbia gave similar results.

Slight phenotypic differences between the two alleles were noted in the Ames grown materials. Mutant kernels of sh6-1295 were uniformly opaque, more extremely shrunken than mutant kernels of sh6-8601, and were frequently embryo lethal. Mutant kernels of sh6-8601 varied from glassy to opaque, were less shrunken than sh6-1295 (and closer to shrunken1 in appearance), and usually produced viable embryos. Kernels heterozygous for both mutant alleles were similar in appearance to kernels homozygous for the sh6-8601 allele. Whether these differences are due to differences in genetic background, or whether sh6-8601 is a less severe, leaky allele, we do not know at this time. 

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