Nick Johnson

Examination of intraspecific pollen competition is imperative for evaluating the evolution of reproduction of flowering plants. Pollen competition to sire seed leads to selection for faster pollen tube growth giving “fast” genotypes an advantage over “slow” genotypes and could isolate populations due to specific interactions between the pollen (male gamete) and the pistil (female organ) that favor certain pollen and pistil genotypes. We hypothesize that pollen genotypes with faster pollen tube growth will sire the majority of seed when competing with genotypes with slower pollen tube growth. The hypothesis was tested using Nicotiana tabacum (tobacco) male donors with known rates of pollen tube growth on a given female were selected to compete against each other. SamR (N. tabacum ‘Samsun’ with transgenic kanamycin resistance) was used as a marked line in all competitions. Despite SamR having slower pollen tube growth vs a competing genotype, it sired more seed than the faster competitor in almost half of the crosses. Potential explanations for these results could include differences in pollen morphology resulting in errors in determining pollen concentration, undetected plant health issues, or male-female factors that also determine seed siring. Future research should test these findings and investigate SamR seed siring success in these competitions.