Oryzeae

Abstract: The phylogeny and evolutionary history of the rice tribe (Oryzeae) were explored using sequences of five DNA fragments (matK, trnL, nad1, Adh2, and GPA1) from chloroplast, mitochondrial, and nuclear genomes. Results indicate that (1) Oryzeae is monophyletic and falls into two main clades corresponding to the traditionally recognized subtribes; (2) previous recognition of three monotypic genera (Hydrochloa, Porteresia, and Prosphytochloa) is not justified; and (3) close affinities of the monoecious genera are not supported, suggesting the possibility of multiple origins of unisexual florets. Based on the magnitude of matK and GPA1 sequence divergence, we suggest that Oryza and Leersia branched off from the remaining genera of Oryzeae ∼20 million years ago (mya), and separated from each other ∼14 mya. A divergence time of ∼9 mya is obtained for the most basal split within Oryza. These estimates suggest that Oryzeae diverged during the Miocene, and thus imply that long-distance dispersal appears to be one of the important factors in the diversification of the tribe.

Abstract: The genera investigated were classified according to Pilger and the position of the tribes Arundinelleae, Phyllorachieae, Stipea and Aristideae in this system of classification was critized. The chromosome numbers of 79 species belonging to 45 genera have been counted. Fifty-seven of these species were recorded for the first time, or chromosome numbers differing from earlier counts were reported. The following genera were previously unknown cytologically: -Schnzidtia (n=9); Phyllorachis (n=12); Bewsia (n=10); Miscanthidium (n=10); Urelytrur (n=10); Chrysopogon (n=10) and Trachypogon (n=10). The inclusion of the genus Ehrharta in the tribe Phalarideae was criticized. It was suggested that this genus should be transferred to the tribe Oryzeae, It was also pointed out that the genus Trtrachne belongs in the Eragrosteae.

Abstract: Plants with characteristics of species belonging to the tribe Oryzeae were present in India more than 60 million years ago (Ma), early in the history of grasses (Prasad et al. 2005). This tribe is now represented by 11 genera that are found in tropical and temperate regions of the world. Among genera in the tribe Oryzeae, the genus Oryza, with about 23 species, has been remarkably successful in evolutionary terms. Species of Oryza with the A and C genomes have a pan-tropical distribution. Rice has been domesticated from wild A genome wild Oryza several times and is the world’s most important staple food. Among cereals, rice has a small genome and is considered as a model for genome studies. The genus Oryza is of particular interest not only because it is the genus of rice but also because of what the genus can tell us about other grasses. The genus Oryza is subject to increased research attention now that the rice genome has been fully sequenced. There are now BAC libraries for species representing most of the genomes of the genus Oryza (Ammiraju et al. 2006). The objective of this chapter is to consider the genus Oryza from phylogenetic and biogeographic perspectives, with emphasis on recent research.

Abstract: Phylogenetic relationships were inferred using nucleotide sequences of the chloroplast gene matK for 26 species representing 11 genera of the tribe Oryzeae and three outgroup species. The sequenced fragments varied from 1522 base pairs (bp) to 1534 bp in length with 15.4% variable and 7.9% phylogenetically informative sites when the outgroups were excluded. The aligned sequences were analyzed by maximum parsimony and neighbor-joining methods. Analyses of the sequence data indicated that species of Oryzeae form a strongly supported monophyletic group, concordant with previous morphological and anatomical evidence. The tribe Oryzeae can be divided into two monophyletic lineages, corresponding to the traditionally recognized subtribes Oryzinae and Zizaniinae. The first subtribe consists of Oryza and Leersia, while the subtribe Zizaniinae includes the remaining genera. The matK sequence data did not support the close affinities of the monoecious genera in Oryzeae, implying the possibility of multiple origins of the floral structures in the tribe. It is noteworthy that Porteresia coarctata is closely related to Oryza species, suggesting that it should be treated as a member in the genus Oryza rather than a separate monotypic genus.