CLONAL REPEATABILITY OF IN-VITRO POLLEN-TUBE GROWTH-RATES IN OENOTHERA-ORGANENSIS (ONAGRACEAE)

The concept that pollen selection is an important force driving angios perm evolution has received a lot of attention in recent years. In ord er for pollen competition to have evolutionary significance, heritable variation for pollen tube growth rate must exist. In this study, I te sted the clonal repeatability, a measure of broad-sense heritability, of in vitro pollen tube growth rate in Oenothera organensis. Although I found significant phenotypic differences in pollen tube growth rate, the calculated clonal repeatability value of 9.4% indicates that heri tability of pollen tube growth rate in this species is quite low. In c ontrast, both flower identity and plant identity had highly significan t effects on pollen tube growth rate, suggesting that the environment may be more important than genotype in determining pollen performance in this species.