The reproductive biology ofJaborosa integrifolia (Solanaceae): Why its fruits are so rare?

Abstract

Jaborosa integrifolia exhibits stigma-height polymorphism. There are individuals with flowers where anthers and stigma are at the same height but the rule is variable herkogamy, the most common type (75%) being that with an exerted stigma. Self- and cross-tubes did not differ in their capability to reach the ovary (t = −0.67,P < 0.53); they had a high growth rate (6.95 ± 2.28 mm h−1). There is not autogamy but mostly self-incompatibility. Fruits from controlled cross-pollination showed the highest seed set and seed viability. The nectar sugar is characterized by a similar amount of glucose and fructose, and by the absence of sucrose. Although nectar secretion was continuous throughout the life of the flower, most nectar was secreted during the first 24 h after flower opening. Nectar production costs appear to be lower than in other species since nectar secretion is neither inhibited after a removal (i.e. a pollinator visit) nor reabsorbed as the flower ages. Sphingids visit the flowers mainly after midnight. They insert their proboscis down to the base of the corolla tube to reach the nectar. The upper limit to fruit production is set by pollinator visits. Fruits produced from open-pollinated flowers are often predated by numerous larvae (mainly lepidopteran ones). Considering that this species is mostly self-incompatible and pollination is limited, that each plant displays only a low number of flowers throughout the flowering season, and that there is a high rate of fruit predation, it is not surprising that fruits ofJ. integrifolia are so rare.