Breeders may choose to produce seeds for the commercial market which are all F1 offspring or sometimes called F1 hybrids. F1 hybrid seeds are important to the grower since, given a uniform environment, all plants of the same cultivar will produce a uniform crop because they are all genetically identical (see Figure 10.10). Crops grown from F1 hybrid seed such as cabbage, Brussels sprouts and carrots can be harvested at one time and they have similar characteristics of yield. Similarly, F1 hybrid flower crops will have uniformity of colour and flower size.
Another feature of F1 hybrids is hybrid vigour. Plants crossed from parents with quite different characteristics will display the feature to a marked extent, giving outstanding growth, especially in good growing conditions. The desirable characteristics of the two parents, such as disease resistance, good plant habit, high yield and good fruit or flower quality, may be incorporated along with established characteristics of successful commercial cultivars by means of the F1 hybrid breeding programme.
F1 hybrid seed production first requires suitable parent stock, which must be pure for all characteristics. In this way, genetically identical offspring are produced, as described in Figure 10.7. The production of pure parent plants involves repeated self pollination (selfing) and selection, over eight to twelve generations, resulting in suitable inbred parent lines. During this and other self pollination programmes, vigour is lost (the parent plants do not look impressive) but, of course, the vigour is restored by hybridization.
The parent lines must now be cross-pollinated to produce the F1 hybrid seed. It is essential to avoid self pollination at this stage, therefore one of the lines is designated the male parent to supply pollen. The anthers in the flowers of the other line, the female parent, are removed, or treated to prevent the production of viable pollen. The growing area must be isolated to exclude foreign pollen, and seed is collected only from the female parent. This seed is more expensive than most other commercial seed, due to the complex breeding programme requiring intensive labour. Seed collected from the planted commercial F1 hybrid crop represents the F2, and will produce plants with very diverse characteristics (Figure 10.8). Some F2 seed, however, is deliberately produced by breeders for flowering plants, such as geraniums and fuchsias, where a variety of colour and habit is required for bedding plant display.
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