MATING STRUCTURE AND INBREEDING AND OUTBREEDING DEPRESSION IN THE RARE PLANT GENTIANELLA-GERMANICA (GENTIANACEAE)

Isolation and small size of populations as a result of habitat destruc tion and fragmentation may negatively affect plant fitness through pol linator limitation and increased levels of inbreeding. To increase gen etic variation in small populations of rare plants artificial gene flo w has been suggested as a management tool. We investigated whether pol linator limitation and inbreeding depression could reduce fitness in G entianella germanica, an endangered biennial of increasingly fragmente d calcareous grasslands in Central Europe. We experimentally excluded pollinators and generated progenies by hand-pollinating flowers with p ollen from different distances. G. germanica was highly selfing. Polli nator exclusion strongly reduced seed set, indicating that pollinator limitation could potentially reduce plant fitness. Germination rate as well as number of leaves and rosette size of progeny from 10-m crosse s was higher than that of progeny from open pollinations, self-, l-m, and interpopulation crosses. After 6 mo of growth differences in the n umber of surviving plants persisted, whereas differences in plant size did not. The results suggest that inbreeding depression may reduce pl ant performance in G. germanica. Outbreeding depression in the perform ance of progeny from interpopulation crosses indicates that caution is necessary in using artificial interpopulation gene how as a managemen t tool.