By Arne LUNDQVIST
Institute of Genetics, Lund, Sweden
Within 15 S1-progenies of diploid Steel-rye, a well-known Swedish commercial variety, genetics of self-incompatibility has been studied by means of selfings, intercrosses, and reciprocal backcrosses to the corresponding parent plant, forced through repeated cloning to a second-year flowering. In all, 170 plants have been studied in 276 crossing combinations. Degree of seed setting on selfing shows a strong positive correlation between parent plants and corresponding S1-progeny groups (gamma=+0.77). The percentage of compatible crosses in the different crossing combinations tried are summarized in the table.
The results obtained indicate that self-incompatibility in Steel-rye is controlled by two multiallelic incompatibility loci, identity at both loci being necessary for full incompatibility. The fact that self-incompatibility in rye is practically unimpaired after chromosomal doubling, may be considered to indicate a sporophytic control of incompatibility. The analysis has been carried on, however, especially in backcross progeny groups (from S1-plants compatible as mother with their corresponding parent plant) and the number of inter-compatible groups within such a progeny has in all cases indicated that the reaction of the pollen in question (from the parent plant) has not been uniform. In four out of five cases analysed, the number of inter-compatible, intra-incompatible groups has been three, exactly the number expected if the parent plant is assumed to be heterozygous in two incompatibility loci with gametophytic control of incompatibility, and the corresponding S1-plant homozygous in one or both of them. The remaining case has given only two inter-compatible groups. In the case of sporophytic control of incompatibility, the pollen reaction being uniform, 4 and 6 inter-compatible groups could be expected in the progeny, if the pollinated S1-plant is assumed to be homozygous in both or only one, respectively, of the incompatibility loci. Therefore, the hypothesis seems probable that self-incompatibility in Steel-rye is gametophytically controlled by two multiallelic self-incompatibility loci. In such case, the haploid pollen, already, will have had an opportunity of becoming adapted to carry more than one allele without disturbing allelic interaction, and this will obviously be enough to account for the self-incompatibility being unimpaired after chromosomal doubling in rye.