Nectar secretion pattern, removal effects, and breeding system ofLigaria cuneifolia(Loranthaceae)

Abstract

Some aspects of the reproductive biology of Ligaria cuneifolia have been studied, addressing the following questions: (i) Are there temporal differences in the female and male functions? (ii) How do nectar composition, volume, concentration, and amount of sugar vary throughout the flower lifetime? (iii) How does the plant respond to nectar removal? (iv) What is the breeding system of this species? Flowers last 4 days. There is a predominance of the male function in the first days and of the female function in the last days. Chemical composition of nectar varies throughout the flower lifetime; there is a constant decrease in sucrose along with an increase in glucose. Nectar is secreted during nights, and every secretion period is followed by a cessation interval. After the final cessation, a period of active resorption follows. During the mostly male phase of the flower, nectar has more sucrose than hexose, its secretion is discontinuous, and nectar removal reduces the rate of nectar production. During the mostly female phase, nectar has more hexose than sucrose, its secretion ceases, nectar removal does not affect nectar production, and a resorption period is inferred. Tests for spontaneous autogamy and apomixis were negative. Low fruit set is obtained when autogamous, geitonogamous, and xenogamous hand pollinations are performed on flowers less than 2 days old compared with flowers at least 3 days old (0, 15, and 47% versus 19, 37.5, and 89%, respectively). These results indicate the the reproductive system of L. cuneifolia is primarily xenogamous, but reproductive success is related to flower age. Keywords: Loranthaceae, Ligaria, nectar chemistry, breeding system, flower phenology, reproductive biology.