PROBLEMS OF HYBRID SEED PRODUCTION

Japanese breeders pioneered the production of F₁ varieties of many horticultural crops in the 1930's and 1940's (Yamashita, 1973). One of the main reasons for their interest in the technique was to protect their varieties from being pirated by competitors but with the introduction of Plant Breeders Rights in many countries this motive is less important now. More or less concurrently workers in the USA were also developing F₁ hybrid vegetabeles utilising various breeding systems (Duvick, 1967). Interest in F₁ vegetables in centred now on the possibilities of plant and product uniformity and the exploitation of heterosis.

The introductin into horticulture and the practical breeding of hybrids in commonly grown crops was a slower process in Europe than the USA and Japan and it is only over the past decade that the special problems of seed production in European hybrids is demonstrated by the increased number of hybrids on the UK National List in 1976 compared to the list of 1973. These are shown in Table 1 for some selected crops, together with the total number of cultivars in each year and the percentage represented by hybrids. Caution is needed in interpreting the figures because the selected years span a period when seedsmen were culling their catalogues following the impact of EEC legislation and also because the list does not always accurately indicate hybrid cultivars. In 1973 there were 11 listed crops in which hybrid cultivars were available, the number dropped to 10 in 1976 due to non-inclusion of aubergines and peppers and the addition of turnips. Increases in the number of hybrid cultivars in crops such as Brussels sprout, cabbage, carrots, onions, spinach and tomato are specially significant in a European context.

The initial breeding of hybrids is costly and the seed production costs are also comparatively high. Furhermore, with our present knowledge of F₁ seed production, it is not possible to prevent the loss of entire seed crops on certain occasions owing to environment factors, or to avoid the need to destroy a crop because of excessive sib proportions. The cost of these failures has to be borne by the successful crops. Dorsman (1976) estimated the latter as 3 to 6 times greater than for open-pollinated varieties of onions, carrots and brassicas. There is no evidence in the National List figures of a withdrawal form hybrid breeding in any major crop despite the elevated seed prices necessary to recoup the initial investments and to cover

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