Abstract
The results of the experiments presented in the two previous papers of this set showed that 35 autotetraploid ryegrass plants fell into 18 different incompatibility classes and, in particular, that only one S-Z pair in the pollen needs to be matched in the stigma for incompatibility to occur (Fearon, Hayward and Lawrence, 1984a, b). These results were obtained by pollinating tetraploids with pollen from diploids and vice versa. In the experiment described in the present paper, the classification and conclusions of these earlier experiments are put to the test by crossing the tetraploid plants inter se. The results completely confirm those of the earlier experiments. In addition, they show that there is no dominance between the alleles at either locus in the pollen and that incompatibility only occurs when both an S and a Z allele are matched in the stigma.
Two implications of these results are considered. First, that only one S-Z pair in the pollen needs to be matched in the stigma strongly suggests that the growth of incompatible pollen is positively inhibited, rather than that of compatible pollen being positively stimulated.
Second, it is shown theoretically that a consequence of this mechanism is that the level of cross-compatibility is appreciably lower in populations of tetraploids relative to those of diploids in which few, but equally frequent alleles are segregating at each locus. If the number of alleles that are segregating in the population exceeds twelve, however, this difference in level of cross-compatibility becomes negligible.
The implications of this outcome for plant breeding are briefly considered.
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Fearon, C., Hayward, M. & Lawrence, M. Self-incompatibility in ryegrass IX. cross-compatibility and seed-set in autotetraploid Lolium perenne L.. Heredity 53, 423–434 (1984). https://doi.org/10.1038/hdy.1984.99
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DOI: https://doi.org/10.1038/hdy.1984.99
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