Pod and seed coat factors in seed dormancy of wild radish (Raphanus raphanistrum L.)

There has been some confusion in the literature about the relative contribution of the pod and seed coat in the expression of seed dormancy in wild radish. Studies were undertaken with two wild radish biotypes (SE and RO). Pods of the SE biotype were collected from plants grown under a rain shelter erected after the flowering stage to impose water stress as well as from plants growing outside the shelter. Collected pods were placed on the soil surface under a transparent rain shelter as well as in the open. Germinability was tested for all the treatments monthly for six months after ripening. All seeds enclosed in pods were highly dormant at maturity and lost their dormancy gradually during winter. There was a higher level of germination in the pods stored in the open compared to those under the shelter, which could be due to the effect of rain on pod breakdown. Seeds produced under water stress conditions in the SE biotype were less dormant than those produced outside the shelter under normal seasonal rainfall. At six months after maturity, removal of pods enclosing the seed increased germination by 1.3-fold in the SE biotype whereas the increase in the RO biotype was 5-fold. Greater response to pod removal in the RO biotype is likely to be due to its thicker pods. Partial removal of seed coat also increased the germination of SE and RO biotypes by 20 and 50%, respectively. The results indicate that both pod and seed coat play an important role in the dormancy of wild radish seeds.