The male pollinator has to restore fertility in the seed collected from the female at harvest. But in the Ogura system, unlike the MSL system, not every pollen-producing oilseed rape plant can “restore” male fertility. That´s because the male sterility gene originally came from radish plants, and was found in the cytoplasm DNA, rather than nuclear DNA. It means the male plant has to be able to switch male sterility off in the cytoplasm, something not every variety can do. Male restorers don’t necessarily have to be of the highest agricultural value. In fact they are quite often varieties you wouldn´t want to grow commercially. They are chosen because the genetics work well together.
Genetic separation of the male and female lines is crucial to the success of hybrids. If you can develop pools of the material genetically separate enough from each other, then you get heterosis, which gives greater hybrid vigour and yields, when you combine them.