Summary

Hybrid varieties of crop plants are grown when the increased productivity gained from heterosis offsets the extra cost of their development and seed production. One important factor in economically viable hybrid seed production is the availability of a practical and effective pollination control system, which is employed to prevent sib- or self-pollination of the female parent. Such a system is not available in many important crops and, in others, difficult and costly manual emasculation of the male flower or flower parts from the female parent plants is the only possibility. Alternative methods of pollination control have long been desired in these crops. The development of recombinant DNA technologies has opened new possibilities for creating and manipulating male sterility for pollination control. These possibilities are the subject of this chapter. Recombinant DNA concepts devised only in the last five years have already developed into practical tools for hybrid seed production and will be one of the first and most important contributions of biotechnology to plant agriculture.

Introduction: The importance and production of F1 hybrid varieties

The exploitation of heterosis through the use of hybrid varieties is arguably the single most important contribution of genetic research to agriculture (Peacock 1992). The term “heterosis,” or hybrid vigor, was defined by Shull (1952) as the increase in vigor and productivity resulting from the differences in parental gametes. Thus, in contrast to the open-pollinated or inbred varieties they replace, hybrid (F1) varieties are derived from controlled crossings between two genetically distinct groups of parents, usually inbred lines. An added premium in the case of hybrids of inbred lines is uniformity, which is often a major parameter of quality and can also facilitate mechanical harvesting.