Summary
An analysis of four families, whose parents are of very different origin, shows that self-incompatibility in diploid Lolium multiflorum is determined, as in L. perenne and other self-incompatible grasses that have been investigated, by a pair of multi-allelic genes whose effect in the pollen is gametophytic. Again, as in L. perenne, one of these genes, defined as S, is linked in its inheritance to the gene, PGI-2, which codes for the enzyme phosphoglucoisomerase, the best estimate of the frequency of recombination between these two loci being p̂=0·2414±0·0795. However, whereas in all previous experiments S and Z appear to have assorted independently, in two of these L. multiflorum families there is evidence that these genes are linked, the best estimate of their recombination frequency being p̂ =0·2807 ±0·0595.
Crosses were made between 27 pairs of plants which included pairs that were expected, on the basis of pollen-stigma reactions, to be incompatible, half-compatible, three-quarters compatible and fully compatible. Fourteen plants were also self-pollinated and ten were allowed to set seed by open pollination. The seed-set obtained from the selfs (0·39 per cent) showed that L. multiflorum is no less self-incompatible than L. perenne. However, the seed-set obtained from incompatible crosses was significantly higher (3·77 per cent) than that obtained from selfs. On the other hand, there were no systematic differences between the three categories of compatible cross which gave an average seed-set of 20·60 per cent. Though there is some overlap between the distribution of the seed-set of these and incompatible crosses, on average these results confirm the classification of the plants on the basis of their pollen-stigma reactions.
A rather approximate estimate of the number of S and Z alleles in the species, based on the number found in the four parents of the families examined, suggests that at least 40 different alleles are likely to be present at each locus.
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Fearon, C., Hayward, M. & Lawrence, M. Self-incompatibility in ryegrass. Heredity 50, 35–45 (1983). https://doi.org/10.1038/hdy.1983.5
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DOI: https://doi.org/10.1038/hdy.1983.5
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