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| ΆΒ Evolution |
| he basic element of biological evolution is generation of hereditary variations,
which are point mutation or change in gene structure, chromosomal aberration,
and multiplication of entire chromosomal set. These variations expand with
genetic recombinations through sexual process and they are selected by their
environmental conditions. It seems that the variations generated in Gondwana
rice evolved into several types of wild rices and then they were differentiated
to cultivated rices. O.sativa and O.glaberrima are closely related to O.perennis and O.breviligulata, respectively. O.glaberrima and O.breriligulata are endemic to Africa, while O.sativa and O.perennis are cosmopolitan. The former two can be distinguished from the latter two by short, roundish, and tough ligules, a small nurmber of secondary panicle branches, death after maturity, and other features. Moreover, these two series, perennis-sativa and breviligulata-glaberrima, are inter-sterile and intra-fertile groups. Therefore, these four species can be subdivided into two phyletic series. O.sativa, which is cosmopolitan, has been again differentiated to three types of common rices, japonica, javanica, and indica as shown in the evolutionary pathway of cultivated rices. |
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