Studies on the genetics of self-and cross-incompatibility in the Japanese radish. (III)

Abstract

1. In these experiments two varieties of the Japan-wese radish, Miyashige and Tenma, were used as materials. Fertility was determined by pollen be-havior on stigmas instead of by seed counts.
2. The results of self-and cross-pollinations in variety Miyashige were very complex. Ten plants examined were divided into eight classes on the basis of cross-relations. All these plants were self-incompatible. In inter-class pollinations there were both cross-compatible and-incompatible combinati-ons. Differences in the reciprocal reactions between certain classes were also found (Diagram 4).
3. These results closely resemble those of the previous papers (TATEBE 1944, 1956), and may well be explained if the following items are assumed:
(a) Self-and cross-incompatibility is controlled by multiple appositional alleles at two loci (S and I). S is assumed to be epistatic to I, but hypostatic to II (S>I, S<II).
(b) The reaction of the pollen is sporophytically determined. A genetic explanation for the results was given in diagram 5. This interpretation is analogous to RILEY's hypothesis on Capsella (1936).
4. On the other hand, the results of self-and cross-pollinations in variety Tenma were much more simple than those of variety Miyashige. All these plants were self-incompatible. Excepting two incom-patible matings, all other combinations were cross-compatible (Diagram 1).
5. These results may well be explained by the following hypothesis (Personate type):
(a) Self-and cross-incompatibility is controlled by multiple oppositional alleles at one locus (S).
(b) The reaction of the pollen is gametophytic-ally determined. A genetic explanation for the results was given diagram 2.
6. However, it is a well known fact that in numerous self-incompatible Cruciferous species the reaction of pollen is sporophytically determined. Judging from this standpoint, it might be assumed that the genetic interpretation of self-incompatibility in variety Tenma was perhaps erroneous, for the data obtained were rather meagre. A solution of the problem still awaits the future.