Differential pollination success in the course of individual flower development and flowering time in Gentiana pneumonanthe L. (Gentianaceae)

The effect of flowering time and anthesis stage on fecundity of Gentiana pneumonanthe L. (Gentianaceae) in a greenhouse experiment was studied. The species is self-compatible, not apomictic, and rarely self-pollinates spontaneously. On average, flowers lived for 11.4 days, starting with a male stage of 3.6 and continuing with a female stage of 7.9 days. Pollen viability was highest during the first two days of the male stage, but never exceeded 50%. Seed-set from cross-pollination was higher earlier in the flowering period (77%) than later (63Vo). For self-pollinations, no significant difference was observed. The success of hand-pollinations declined dramatically after the fourth day of the female stage. Self-pollination yielded lower seed-set on the first day of the female stage than on the following three days. Also, there was a significant difference in seed-set between self- and cross-pollinations (25% vs 55%, respectively) only on the first day. This suggests that selection against self pollen was stronger during the first stage of the female phase and weakened as the stylar tissue aged. In conclusion, two different ways to enhance outcrossing were observed: (1) within the population's flowering period, and (2) within an individual flower's lifespan. Both may have important effects on the genetic variability of G. pneumonanthe offspring under unfavourable conditions. Wese include small population size (associated with reduced pollinator service), general pollinator scarcity, or rainy summers.