Why are the seed pods so large after self-pollination in broccoli?

Broccoli self-pollinated, pods large but no seeds set, what's going on? Broccoli belongs to the cruciferous family, and in the cruciferous family a phenomenon often exists: self-incompatibility! What does that mean? That is, its own pollen pollinating its own pistil fails to set seed.

The self-incompatibility phenomenon is also very common in cruciferous crops such as rapeseed and Chinese cabbage, and in breeding there is often the hope of using stable self-incompatible lines to produce hybrids. At Academician Fu Tingdong's group at Huazhong Agricultural University there are many self-incompatible line rapeseed resources.

Self-incompatibility is related to many factors such as temperature and developmental stage, and since the failure to set seed under selfing is most likely this situation, there is no need to make a fuss. If you want seeds to set, you can try crossing with pollen from other plants; if seeds do set, then the above conjecture is confirmed.

As for the relatively large pods, this is due to the failure to set seed. You can observe that pods that have not been pollinated and set seed are all relatively large; after all, the plant supplied so much nutrition for reproducing offspring, yet the pods are empty shells, so the nutrition can only be consumed in the development of the pod wall.

The above is only my speculation, since I have not seen photos or the specific operation process. I hope it is helpful to you.