Re-evaluation of alien wild genes in rice

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Considering that genetic erosion is occurring at an accelerating rate through the world, it is urgent to evaluate and use alien genes. To overcome difficulties associated with gene transfer from alien species, we must learn more about the basic knowledge on crop genepools. Here, we examined constraints in using wild rice relatives in breeding.Unidirectional cross-incompatibility was detected when a segment of chromosome 6 was introduced from wild rice into a cultivar. When pollinated by Japonica type, the plant with the segment showed reduced seed setting while the reciprocal showed normal seed setting. Cytohistological observations revealed that retardation of the endosperm caused abortion of seeds. Genetic experiments revealed that a gene controlling incompatibility in the female parent as well as a gene (s) controlling compatibility in the male parent was located on the segment. Furthermore, Japonica type tended to show reduced seed setting compared to Indica type and wild rice. A segment of chromosome 7 was also examined after introducing it into a cultivated form from a common wild rice. The genetic diver-gence on the segment is needed to be studied since weedy forms frequently show red pericarps even after introgression, suggesting the adaptive significances of the segment under natural conditions. Two dominant genes were detacted to be located on the segment. One was responsible for short stature only in the vegetative phase. The other gene was responsible for photosensitivity. Distorted segreations were detected and the introduced segment seemed to be quickly eliminated as the plants become similar to cultivated type. Thus, internal constraints between different taxa are needed to be studied for efficient uses of alien genes.