Investigation of a self-compatible mutation in Solanum tuberosum clones inhibiting S-allele activity in pollen differentially

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A self-compatible (SC) mutation, identified in dihaploid lines of Solanum tuberosum, was investigated. It has previously been proposed that this mutation arose by translocation of an S-allele (S1) to a new chromosomal location. When present in pollen grains of genotype Sx, it overcomes the incompatibility reaction normally seen on styles carrying the Sx allele. However, when present in S1-bearing pollen grains, the normal incompatibility reaction on styles carrying S1 is still observed. Using probes for the potato (S. tuberosum L.) S-linked glycoprotein (SLG) genes, it is shown that no sequence derived from SLG allele S1 can be linked to the presence of the SC mutation. The polypeptide product of the SLG allele S1 is also not detectable in SC mutant lines unless the S1 allele is also present. It is concluded that the SC mutation arose in a sequence other than that encoding the SLG S1 polypeptide, either in a part of the S-locus that is distinct from the S-gene, or at a different locus, giving rise to an inhibitor.