Studies on the Genetics of Self- and Crossincompatibility in the Japanese Radish (1)

Abstract

1. In the present experiments, Tenma, a cultivar of the Japanese radish, was used as material. Fertility was determined by pollen behavior on stigmas instead of by seed counts.2. The results of self- and cross-pollinations showed that all plants tested were self-incompatible. Excepting a few incompatible matings, all other combinations were cross-compatible (Fig. 1 and 2).3. Self- and cross-pollinations were attempted in the sister plants obtained by bud-selfing two self-incompatible plants (No. 8 and 6 in 1959).4. In the selfed progeny of No. 8, ten plants tested were divided into three classes on the basis of cross-relations (α, β and γ). All these plants were self-incompatible. Two classes, α and β, were cross-compatible in both directions. On the other hand, class γ was cross-compatible in a combination, β×γ, but cross-incompatible in all other combinations (Fig. 3).5. In the selfed progeny of No. 6, ten plants tested were divided into two classes (α and β). All these plants were self-incompatible. The combination between α and β was compatible, but the reciprocal was incompatible (Fig. 4).6. The data presented in Fig. 1 and 2 may be explained if the following items are assumed:(a) The self- and cross-incompatibility is controlled by a series of multiple alleles at one locus (S1-S6)(b) No dominance relation between S genes.(c) The reaction of the pollen is gametophytically determined (the Nicotiana-type).By this hypothesis, however, the results of Fig. 3 remain unexplained (Fig. 5a).7. All these results may well be explained by the following hypothesis:(a) The self- and cross-incompatibility is controlled by a series of multiple alleles at one locus (S1-S9)(b) The dominance relation between S genes in the pollen (S1, S4, S7, S8>S9, S6>S2).(c) The reaction of the pollen is sporophytically determined (the Crepis-type).A genetic explanation for the results was given in Fig. 6 and 7.8. Following this hypothesis, three classes (α, β and γ) were expected to appear in the selfed progeny of No. 6, while only two classes (α and β) were found as indicated above. It is thought that the plants belonging to class γ were probably ruled out during the experiments, owing to the lack of vigor and feeble growth (Fig. 8).In short, the results of self- and cross-pollinations in variety Tenma were different widely from those reported earlier (1944, 1956 and 1958). At a glance, the genetic behavior of incompatibility seemed to be the Nicotiana-type. However, the pollination experiments of the selfed progenies suggested the more complex relations existing between them. From the results obtained it is concluded that the genetic behavior of incompatibility in variety Tenma may be the Crepis-type.