This paper describes a method of obtaining pure stands of F1 hybrids even if selfing occurs, e.g. the male-sterility is imperfect. The procedure is based on the use of recessive nutritional (auxotrophic) gene(s). The F1 hybrids of the auxotroph x prototroph crosses are phenotypically and physiologically normal. The self- or sib-pollinated auxotrophic parental line(s) produce lethal offspring in the absence of the required nutrient. In crosses involving functional male-sterile maternal lines and thiamine-dependent male tomato lines (or reciprocals), the described scheme works as predicted. This scheme is now being employed in the production of hybrid tomato. Although some problems were experienced during the preliminary work with barley mutants the overall results are promising. The hybrid-production scheme has various advantages: (1) it is applicable in normally selfing species, too. (II) the two parental lines can be blended in hybrid crossing blocks, thereby increasing cross pollination, (III) it involves a genetically determined built-in system for selective elimination of the plants of unwanted constitution, and the scheme can therefore be used with imcomplete male- or self-sterile lines, too.
