| Self-sterility in autotetraploid rye A. LUNDQUIST Institute of Genetics, Lund, Sweden Self- and cross-incompatibility reactions of the pollen in diploid rye are controlled gametophytically by two apparently multiallelic and independently segregating loci. Haploid pollen with only one of its two factors common to the style has no functional disadvantage, and the incompatibility specificities must be considered to result from a direct complementary cooperation between the two loci. Upon chromosomal doubling self-incompatibility is retained in rye. Among 974 plants studied by the present writer and obtained from elite populations of the tetraploid strain of Steel-rye, a Swedish commercial variety, no completely self-compatible plant was obtained, 80-85% of the plants setting 0-5% seed upon selfing. Self-incompatibility is, thus, quite pronounced in the tetraploid strain, but the tetraploids upon selfing set slightly but significantly more seed than do the diploids. Between populations of different years the tetraploids display a considerably higher variability in seed setting upon selfing. In the S1 generation obtained from population plants with less than 5% seed setting upon selfing, plants highly fertile upon selfing are obtained-but much more rarely in the tetraploids. In most cases this high fertility upon selfing is retained in later S generations. Such plants may result in the diploids from a loss mutation at the pollen controlling part of an incompatibility locus. In the tetraploids the true nature of such highly fertile plants has not been settled, but in any case tetraploid truly self-compatible mutants must be considered much rarer. Data from intercrosses between known doubled genotypes show that two homologous alleles of the diploid pollen common to the style, will not be able alone to render the pollen incompatible. Upon intercrosses in four tetraploid S1 families, obtained from selfed elite population plants of unknown genotype, an ununiform reaction pattern within groups of reciprocally incompatible plants, was frequently encountered. The combined evidence points to the view that in the diploid pollen the single incompatibility locus is not able alone to produce inhibitioh of pollen tube growth. The pollen specificities result from cooperation between the two loci within pairs of factors. One such factorial pair of the polen common to the style is sufficient to render the pollen incompatible. The lower frequency of self-compatible mutants obtained after selfing in the tetraploids can thus be easily understood. In a haploid pollen, containing a mutated "self-compa- tibility" factor, cooperation between matched, not identical incompatibility factors will no longer be possible ; but correspondingly in a diploid pollen several ways of such factorial cooperation may be left possible. A "self compatibility" mutant factor will accordingly behave in a "recessive "way m the diploid pollen and in a "dominant" way in the haploid pollen. (Received April 17, 1957) |