The North American species of manihot delimited by computer aided taximetric methods / Subramaniam Ganapathi Appan.

Tese (Ph.D.)-- University of Colorado, 1969.

Interest in the genus Manihot has grown significantly, of late, as a consequence of Manihot esculenta Crantz (the worlds fifth major staple food crop) emerging as a crop of vital importance to several developing nations. Since the publications of the major treatise on this genus by Pax in 1910, the biological species concepts have been refined and enriched considerably, and Pax's delimitations now tend to be biologically unsatisfactory especially from a plant breeding point of view. These delimitations were based on nebulous criteria and the high degree of leaf polymorphism of Manihot, inadequate field knowledge of these populations, and lack of sophisticated delimitation procedures lead to several misconceptions in his treatment. Therefore Pax's species in the light of our modern concepts. The numerous wild species of Manihot represent a practically unexplored and unexploited reservoir of potentially valuable genetic variability which can be drawn on and utilized in a program of genetic engineering of the crop cassava (Manihot esculenta Crantz) to mold it to suit man's needs better. The key and fundamental step in such an interespecific breeding program is to accurately delincate the closed gene pools of Manihot in order to facilitate drawing population samples from them to be subjected to systematic evaluation of their biological properties especially the qualities significant from a cassava crop improvement point of view. The conventional taxonomic delimitation processes were found to be inefficient for a systematic analysis of complex populations as that of Manihot. This necessitated the development of powerful methods. The computer aided efficiency of modern electronic data processing equipments. The method deploys a series of interlinked computer porgrams, the sequential and integrated application of which, renders possible the delimitation of closed gene pools with precision and confidence. The sequential steps of these procedures are depicted in the form of explicit flow in this dissertation. Extensive field studies were carried out to gain an accurate understanding of Manihot field populations. The numerous field trips provided rare opportunities for gathering critical field data and abundant herbarium material. This not only enabled us to generate substantial basic data, commensurate to the needs for a scrupulous computer analysis, but also significantly enhanced the soundness and confidence of the decisions made in this study. The results of the study of the North American segment of the genus Manihot have been embodied in this dissertation. The South American segment is to be considered as the next phase. The 20 species which together constitute the North American segment of Manihot and the single closed gene pool representing the monotypic genus Manihotoides have been delimited. The gross morphology of these species have been described, their geographical domains have been delineated and their ecological adaptations have been defined. The findings of this study not only qualify to constitute the foundation for instituting cassava improvement programs, but also serve as a model for delimiting and defining species (closed gene pools) with efficiency and precision by employing computer aided methods.

Orientador: Rogers, David J.