The breeding of hybrid varieties and the production of hybrid seed in spinach

In spinach the breeding of hybrid varieties is attractive because this may result in a heterosis and/or a transgressive effect. Resistance to downy mildew Peronospora spinaciae (Mont.) de By] and against mosaic (Cucumis virus 1) can be combined rather easily, since in both cases the resistance depends on one dominant gene. Besides a hybrid variety excludes the growing of later generations.However, a careful removal of all pollen-producing plants demands so much labour that a production of hybrid seed on a commercial scale involves great difficulties. The creation of an entirely female variety would be a solution for this problem. An outline has been given of the way in which such a variety can be developed, starting from purely female and from intersexual plants.It is possible to simplify the production of hybrid seed by using a round-seeded female parent and a prickly-seeded male parent. Moreover this will prevent errors: all plants can then be harvested and threshed at the same time and in cleaning the prickly seed can be separated mechanically from the round-seeded commercial seed. The use of a prickly-seeded male parent will be an extra check on the possible growing of later generations by others.