Diploid F<SUB>1</SUB> hybrids produced from the cross between tetraploid and diploid race in <I>Oryza satira</I>, L. (Preliminary note).

Abstract

(1) In this preliminary note, the author wishes to report an unexpected inheritance in Oryza satira, L. Having in mind the possibility of producing a triploid hybrid, crosses were made between the teraploid strain of rice plant (2n=48) named “TKB” _??_ and the diploid cultivated strain (2n=24) “Taichu 65-Go” _??_. Unexpectedly, all of the F1 hybrids were diploids having the combined characteristics of both parents.(2) The maternal plants, “TKB” are progenies of a tetraploid which has been induced artificially With X-ray radiation by K. Ichijima (1934). Since then, the progenies of this mutant have been cultivated continuously as the stable tetra-ploid strain.(3) In general appearance this tetraploid differed from either its original strain or “Taichu 65-Go”, such characterisitis as rough-arranged panicle, large spikelet and awned glume being, in particular, noticeable. The very low percentage of fertilization (mean, 33.6%) in this plant should be specially mentioned here (Figs. 1, 3 and 4). For the pistillate material, two panicles were chosen from two different tetraploid individuals, i.e. one panicle was used in each plant.(4) “Taichu 65-Go”, or the pollen parent, was known to he a pure cultivated strain. It was clearly different not only from the pistillate parent, above deseribed, but also from the original strain of this tetraploid, in that, the “Taichu 65-Go” has sloping-shouldered and poorly-haired glume, the apicula or which are noticeably colored.(5) In the two crosses, named No. 19 and No. 20, eight and ten spikelets were smeared respectively with pollen of “Taichu 65-Go”. Eleven F1 progenies were obtained in this way from these cross pollinations of these eight plants were obtained to have fully developed.(6) Five of the F1 progenies, i.e. all three from cross No. 19 and two out or the five progenies of cross No. 20, were nearly equal to the pollen parent in general appearance : namely, they have densely-arranged panicles, awnless and smaller spikelets, and deep colored apicula (Figs. 2, 3 and 4). The last characteristic is especially noticeable. It should he further mentioned here, that there is a close resemblance between the diploid hybrid and the pollen parent as regards high percentage of fertilization (mean, 74.2%). On the other hand, the characteristics or these plants were the same as those of the maternal parent, that is to say, the glumes were deeply-haired and broadly-shouldered.(7) The somatic cell divisions at the root tips of these plants were very regular, 24 chromosomes being counted at the metaphase.(8) On the other hand, the remaining three plants in cross No. 20 closely resembled the maternal or the tetraploid parent in general appearance. On examination of the somatic cells at the root tips, all of them were found to be tetraploid (2n=48) as the author had expected. The author considers these tetraploid progenies to have been produced by selling as a result of the failure of pollination.(9) The following three assumptions may be made as a possible explanation of the production of the diploid F1 progenies from the cross of tetraploid _??_×diploid _??_ : (i) Diploid parthenogenetical phenomena may have been due to the stimulation of pollination. (ii) The pistillate plant may be a chimera having diploid and tetraploid shoots, and accidentally the pollination may have been taken place on this diploid shoot. (iii) Elimination !of il. genoin may be carried out during macrogenesis.(10) The first assumption call not suitably explain the author's experimental results, since the diploid hybrids had the characteristics of both parents.(11) According to the results of cross No, 20, the tetraploid progenies were produced by selling, and the diploid ones by crossing on the same panicle. These results can no