Biosystematics of Oryza ridleyi Hook.

The results of the morphological study showed the presence of three district groups: (1) an Oryza ridleyi group represented by the accessions from Thailand and one from Malaysia (2) the O. longiglumis group together with O. ridleyi accession from Malaysia, and (3) the O. ridleyi accessions from Papua New Guinea and Indonesia. Univariate and multivariate analyses revealed that the accessions can be differentiated in terms of anther length, sterile lemma length to spikelet length ratio, and the number of tillers and panicles. The O. ridleyi accessions from Thailand showed long anthers, low sterile lemma to spikelet length ratio, and a high number of tillers and panicles. Most O. longiglumis accessions showed short anthers, a high sterile lemma length to spikelet length ratio, and fewer tillers and panicles. Intermediate anther length and sterile lemma length to spikelet length ratio were shown by the O. ridleyi accession from Malaysia, Indonesia, and PNG. The PNG accessions also uniquely possessed compact panicles. O. ridleyi showed extravaginal buds and a tendency to having an acute ligule shape in contrast to the intravaginal nodal tillering and almost truncate ligules in O. longiglumis. The morphologically distinct O. ridleyi accessions from Thailand and Malaysia were also highly homogenous at the isozyme and molecular levels. At these levels, the O. longiglumis accessions were heterogenous and did not form a cohesive group upon cluster analysis. The O. ridleyi accession from PNG was more similar at the isozyme and molecular levels to some of the O. longiglumis accessions. At the isozyme level, O. longiglumis populations showed a relatively higher level of mean heterozygosity than the O. ridleyi accessions. The hybridization study revealed easy crossability in both intraspecific and interspecific crosses. However, the number of hybrids was generally low, although interspecific crosses specifically with O. longiglumis as female parent produced a number of hybrids comparative to that of the intraspecific crosses. This study clearly showed that despite the presence of morphologically distinct groups, differences at the isozyme and molecular levels within the O. ridleyi complex were not as distinct. The comparative frequency by which seeds and hybrids were obtained from intraspecific and interspecific crosses also suggest a close genetic relationship of the accessions within this complex