DIFFERENTIAL SEED MATURATION UNCOUPLES FERTILIZATION AND SIRING SUCCESS IN OENOTHERA-ORGANENSIS (ONAGRACEAE)

This study examines ovule fertilization and seed maturation success in an evening primrose, Oenothera organensis, using transgenic plants. T he reproductive success of several pollen donors was compared using in dividuals transformed with the GUS (beta-glucuronidase) marker ne whic h allowed the genotype of developing ovules to be determined prior to seed abortion. This marker gene allowed us to discriminate between a p ollen donor's success in fertilizing ovules and its success in siring seeds. Transformed plants had decreased microgametophytic vigour, as e videnced by lower than expected fertilization success in vivo and slow er pollen tube growth rates in vitro. However, transformation had no a pparent effect on offspring sporophytic vigour, including seed mass, s eedling emergence and dry weight. This illustrates the effectiveness o f fertilization competition in screening out poorly functioning haploi d genomes as suggested by Mulcahy (1979). We found significant differe nces between the percentage of ovules fertilized and the percentage of seeds sired by a pollen donor in four of eight cases. Hence, fertiliz ation success does not always predict seed paternity. The proportion o f seeds sired by the transformed donor with very low fertilization suc cess increased, whereas the proportion sired by the donor with relativ ely high fertilization success was reduced. This resulted in nearly eq ual siring ability for the two donors in spite of their difference in fertilization ability.