Pollen viability,vigor, and competitive ability in Erythronium grandiflorum (Liliaceae)

To determine how the capability of pollen is affected by lengthy exposure to field conditions, we obtained pollen samples (from Erythronium grandiflorum) that were fresh (from newly dehisced anthers) or aged, from 6 to 24 hr. Without pretreating the collected grains, we compared their abilities 1) to retain viability, as indicated by the Heslop-Harrison fluorochromatic reaction (FCR) test; 2) to retain germinability, as indicated by pollen-tube growth in vitro on Brewbaker-Kwack medium; 3) to sire seeds when used as a pollen donor on recipient flowers in the field; and 4) to sire seeds competitively when mixed with another donor pollen in competitive pollinations. FCR scores declined drastically with pollen age. Germinability typically declined with age, but less drastically; the correlation between FCR and germinability ranged from strong to nil in different trials. The sharp decline in FCR was probably due to nonlethal, reversible desiccation. Seed-siring success, both in competitive and noncompetitive trials, bore no relation to pollen age or to germinability. Any loss in seed-siring ability in E. grandiflorum pollen over 24 hr is apparently overwhelmed by other sources of variation. The lack of correlation between seed-siring ability and FCR or germinability scores means that those tests should not be used to estimate overall pollen competence in this species. They should be so used in other species only if experiments have demonstrated their greater reliability.