Résumé
Genetic divergence among traditional rices from Madagascar was investigated on the basis of 39 morphophysiological traits and 19 isozyme genes. Comparison with Asian and African rices revealed the existence of new varietal types that do not fit the existing classification schemes. These types are mainly lowland cultivars grown in the high plateau region at altitudes ranging from 1,000 to 1,500 m. Based on morphophysiology, they are intermediate between indica and tropical japonica types for most traits, although they are the tallest. Isozyme data show a limited global gene diversity and a marked bipolar structure similar to the classical indica-japonica structure with, however, a peculiar predominance of allele 2 at locus Amp-1, forming multilocus types that are rare or absent in Asia. Classical associations between some isozymes and some morphological traits are almost nonexistent. The introduction of rices from Asia to Madagascar was thus probably accompanied by a strong founder effect and was followed by intensive intersubspecific recombination. Adaptation to new ecological niches took place without pronounced disruption of subspecific complexes of coadapted genes.