PHENETIC SIMILARITY AND PHYLOGENETIC RELATIONSHIPS AMONG STRAINS OF ORYZA PERENNIS, ESTIMATED BY METHODS OF NUMERICAL TAXONOMY.

Abstract

The relationship between taxa can be estimated from different viewpoints: (a) comparison of characters ranging from protein structure to outward appearance (phenetics, if overall similarity is considered), (b) crossability, meiotic chromosome behavior, fertility and other features of hybrids, (c) ecological and distributional features, and so on. These represent different aspects of relationship between existing taxa, but do not necessarily indicate phylogeny. The advances in numerical taxonomy, however, have inevitably tempted workers to consider the possibility of deduction of phylogeny by numerical evaluation of information obtained from existing organisms (Doolittle and Blomback, 1964; Camin and Sokal, 1965; Wilson, 1965; Throckmorton, 1965; Fitch and Margoliash, 1967; Cavalli-Sforza and Edwards, 1967; Horne, 1967). Oryza perennis Moench is a wild species distributed in swampy habitats throughout the humid tropics, and is a complex of different forms. Usually its strains are classified into Asian, African and American forms or groups (I. R. R. I. 1964, p. 251252). The taxonomy and nomenclature of this species have been a matter of controversy among taxonomists; Tateoka (1963) considered the African form as a distinct species, 0. barthii A. Chev., and called other forms 0. rufipogon Griff., while Henderson (1964) considered all three forms as subspecies of 0. perennis. The present writer takes the latter view. The Asian annual form has become known under various names, for instance, 0. sativa f. spontanea Roschev. or 0. sativa var. fatua Prain or 0. rufipogon subsp. rufipogon. It is considered here as a form of 0. perennis, since the strains of the Asian group show a continuous array of intergrades between perennial and annual types (Morishima et al., 1961). Further, the present work suggests that certain strains from New Guinea and Australia may be considered as a new, Oceanian, form. The various strains all have the same number of chromosomes (n = 12), and can be hybridized with one another. The F1 hybrids show no disturbance in meiotic chromosome pairing, but show sterilities of varying degrees and some other deteriorative phenomena (Chu et al., 1969). The strains are adapted to different kinds of ecological niches and differ in their breeding system (Oka and Morishima, 1967). We initiated studies of this species because its Asian perennial form was considered to be the progenitor of cultivated rice, Oryza sativa L. (Oka and Chang, 1962; Oka, 1964). For a systematic investigation of variations within 0. perennis, data for various characters of the strains and their F1 sterility relationships were analyzed by methods of numerical taxonomy. This paper deals with the methods and results, distinguishing between the phenetic and phylogenetic standpoints. An attempt was made to introduce a relative time scale into the diagram showing the hypothesized phylogenetic relationships of the strains.