F₁ seed production of hybrid rice is practiced in Chine by planting a male sterile line and a pollinator line in alternative rows. This planting method is rather complicated and needs a great manpower. By mixing the seeds of a male sterile line and a pollinator line, mechanized cultivation is feasible for seed production. This method ensures a higher ratio of seed-set on the male sterile plants because the average distance between the pollinators and male sterile flowers becomes closer than that under the alternative-row method. The seeds are harvested in a mixed from of pollinator seeds and F1 seeds. Separation of the F1 seed from a mixed harvest could be made, if the F1 seeds are different from the pollinator seeds in color, size or other traits. If a female sterile pollinator is made available, F1 seeds are only harvested. Another possible method for separation is to incorporate a herbicide-sensitive gene to a pollinator, which should be subjected to a spray of the specific herbicide just after pollination: then all the harvests are F1 seeds only.