Historical and evolutionary origins of cultivated vanilla

This dissertation signals the first examination of the origins and diversification of cultivated vanilla, the world's most popular flavor and, by unit weight, among the most valuable of spice crops. After critical analysis of the evolutionary history of the genus Vanilla [Orchidaceae] and the written history of vanilla cultivation in Mesoamerica, two studies using molecular markers address the genetic diversity, relatedness and origins of Mexican/Bourbon vanilla, Vanilla planifolia Jacks., and the putative hybrid origin of the enigmatic Polynesian cultivar, Vanilla tahitensis J.W. Moore. The principal hypotheses tested are: (1) cultivated vanilla in the Indian Ocean region (Madagascar/Reunion) has derived from a single genetic individual (clone), (2) cultivated vanilla originated multiple times in Mesoamerica, first among cacao producers in Maya speaking Guatemala, Chiapas and Belize, and then later among the Totonac of the Papantla region of Veracruz, and (3) V. tahitensis is a morphologically intermediate, hybrid descendent of V. planifolia and V. odorata C. Presl. The results of an AFLP genotype survey of one hundred cultivated and non-cultivated accessions of Vanilla revealed low levels of genetic diversity in Indian Ocean cultivars, but were unable to demonstrate conclusively that all variation was clonal rather than between non-clonal siblings. Indian Ocean cultivars demonstrated close genetic affinities to cultivated vanilla in Veracruz, Mexico, implying a shared ancestry. Genotypes recovered from cultivated vanilla in Oaxaca and Chiapas are distinct, and have not been found outside of Mesoamerica. Cultivation of vanilla in Oaxaca agro-forests is unique also for its multi-species composition. A combined nuclear (ITS) and plastid DNA (trnH-psbA) sequence analysis of phylogenetic relationships among V. tahitensis and its putative parental species supports a recent hybrid origin for V tahitensis with V planifolia serving as a cytoplasmic donor, and V. odorata contributing as a paternal ancestor. Topological incongruence in phylogenetic tree topologies also raised the possibility of natural hybridization involving the parental species. In contrast to expectations that a strict practice of asexual propagation (via cuttings) would prevent sexual reproduction from occurring in cultivated vanilla, the most parsimonious explanation for the origins of V tahitensis requires a minimum of three sexual generations.