Phylogenetic Relationships in Dioscorea, The True Yams

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

ABSTRACT A grant has been awarded to Geeta Bharathan at SUNY at Stony Brook to study the evolutionary relationships of Dioscorea (the true yams). Dioscorea is a large, economically important monocot genus that contains about 600 species of, mostly tropical, vines that grow in a range of habitats. Despite its traditional value as a tuber and medicinal crop (and, recently, in the pharmaceutical industry) the taxonomy of Dioscorea is in a mess. While a statement, over a 100 years ago, by the famous taxonomist, Hooker, that "...the species of Dioscorea are in a state of indescribable confusion" is slowly being remedied through heroic efforts by a great many alpha-taxonomists, the question of higher level relationships is a thorny one that traditional morphological approaches alone may not be able to resolve. In this project species of Dioscorea across the world will be sampled to study variation in molecules (DNA sequences of three genes) and morphology (observations on field and herbarium collections). Molecular sequences will be analyzed to formulate hypotheses of evolutionary relationships and to construct a systematic framework for the group. This will help to achieve several goals: 1) Evaluation of previous classifications to facilitate taxonomic revisions; 2) Evaluation of the evolutionary basis for particular subgroups (e.g., the one that includes the three North American species) to help understand the historical origins and biogeographical spread of this large genus; 3) Evaluation of morphological traits to improve their use in classification of the genus; 4) Compilation of a morphological data set for phylogenetic analysis, to be done in collaboration with Dioscorea scientists across the world. The wider significance of the achievement of the above objective has both scientific and societal aspects. The project would generate a rigorous systematic framework that then can be used to study various aspects of this important tropical crop: evolution of vegetative form and development (including leaf form and tuber-formation), biogeographical patterns of diversification, and history of domestication. All these would contribute to future uses and improvement of the crop. The project would enable training of students (graduate and undergraduate) in field and laboratory methods including morphology, while at the same time exposing them to important international issues involved in the collection and utilization of germplasm from other nations. The project has the explicit involvement of a Mexican collaborator for plant collection and mapping using GIS, and a course on phylogenetics to be taught in Mexico by the PI. All these activities will contribute to building 1) a scientific base of knowledge on an important, but understudied, tropical crop, 2) scientific skills and infrastructure at the national and international levels, and 3) international collaboration and scientific exchange.