Reproductive biology in two Genisteae (Papilionoideae) endemic of the western Mediterranean region: Cytisus striatus and Retama sphaerocarpa

We studied the reproductive biology of two leguminous shrubs endemic of the western Mediterranean region Cytisus striatus (Hill) Rothm. and Retama sph aerocarpa (L.) Boiss. The former is polliniferous, and the latter is nectar iferous, with maximum nectar production at the earliest hours of the mornin g. Germination of the pollen grains in the flowers of the two species occur s only after rupture of the stigmatic surface. It is also necessary in both cases that pollinators (mainly Apis mellifera) visit the flowers for fruit and seed set to occur. A study of the pollen-pistil interaction indicated that there exists prezygotic self-incompatibility in these two species, pro bably of the gametophytic type, but some self-pollen tubes escape this cont rol and self-fertilize some ovules. However, after hand self-pollination, f ruit and seed set is very low for both species. This suggests the existence of a postzygotic rejection mechanism, which could be due either to the exi stence of late-acting self-incompatibility or to an early action of inbreed ing depression, although there are lines of evidence that seem to point to the second possibility. Hand cross-pollination led to an increased number o f fruit and seeds per plant relative to the control plants, indicating that reproduction is pollen limited.