DIFFERENTIAL SUCCESS OF POLLEN DONORS IN A SELF-COMPATIBLE LILY

If pollen donors are equally effective at siring seeds, the presence o f equal proportions of pollen from two pollen donors on a stigma will lead to equal proportions of seeds sired by each pollen donor. Variati on in germination rates, pollen-tube growth, and embryo viability may cause one donor to sire more seed than another. We looked for differen tial donor success in the field by simultaneously applying equal amoun ts of pollen from two pollen donors. We simultaneously applied equal a mounts of self and outcross pollen to receptive stigmas and simultaneo usly applied pollen from two donors at different physical distances fr om the recipient. Following simultaneous application of self and outcr oss pollen, significantly more of the seeds were sired by outcross pol len donors. Seed set following simultaneous application of two outcros s donors was also nonrandom. Pollen donors from 100 m were more likely to sire seeds when competing with pollen from plants nearby (1 m). To determine whether pollen-tube growth rates were responsible for these patterns of paternity, we varied the timing of deposition of outcross pollen allowing self pollen tubes a head start on the stigma. Outcros s pollen was applied 3 or 24 h after self pollen. In spite of this tim e delay, the majority of the seeds were again sired by outcross pollen . There was no significant difference in the amount of seeds sired by self pollen between the two delay treatments. This result suggests tha t mechanisms operating after ovule fertilization may contribute to the discordance between the proportions of the pollen present and the pro portions of seeds sired.