A Cytotaxonomic Study of Oryza minuta and O. officinalis

Abstract

The 36 collections belonging to the complex of Oryza minuta and O. officinalis gathered during a recent exploration of the major islands of the Philippines were studied cytotaxonomically. Chromosome counts showed that 15 collections were diploid (2n=24) and 21 collections were tetraploid (2n=48). Morphological features of the diploids and the tetraploids were compared, and obvious differences were found in spikelet breadth, shape and certain inflorescence features. It was pointed out that these morphological differences are parallel to those between O. minuta and O. officinalis according to Tateoka's8) amended designation. The geographical distribution of the diploids and the tetraploids in the Philippines was surveyed, and some difference in localization was noted. Our field observations were in favor of the assumption that these two taxa were reproductively isolated under natural conditions. It was concluded that the diploid and the tetraploid plants are reasonably separated at the species level: the former falls under O. officinalis while the latter accords with O. minuta.