1951 Volume 26 Issue 1-2 Pages 13-29
(1) The author is engaged in studying the inheritance of the quantitative characters and the qualifying function of the causal genes in some main crop plants from the view point of plant-breeding. This report is one of the results of experiments on the inheritance of the size and form of grains in rice.
(2) The materials used in this work are the progenies of “Sodairyu”.times;“.ekitori -No.-120”. which were used in the previous report (Syakudo, 1949) for studying the inheritance of panicle length. The total numbers of lines and individuals observed are 494 and 55725 respectively.
(3) “Sodairyu” is a distinguished variety provided with long and loose panicles with large grains, three dimensions of which are about 7.4mm, 3.2mm and 2.2 mm.. “Sekitori-No.-120” is a common variety having short and compact panicles with small grains, three dimensions of them being about 5.3mm, 2.9mm and 2.0mm.
(4) The conditions of cultivation and the methods of investigation are the same as those already described in the writer's report. (Syakudo, 1948). For the measurement, a single grain located on the primary rachilla, nearest to and beyond the uppermost secondary rachilla, was used for each individual at about the middle part of the standard ear (Syakudo, 1948-a). The grain seemed to have been grown always normally, and present the representative value of all the grains of the individual.
(5) The progeny tests in regard to the grain length and the density of the grains in the panicle were made, taking in consideration the mean value, the standard deviation, the coefficient of variability and the range of variance. The results show that the two multiple genes Gr1, Gr2 and a gene. Ka which mainly governs the density of grains in the panicle determine the grain length. Thus the genotypes of the parents will be assumed as follows:-
Sodairyu: C. Gr1Gr1Gr2Gr2kakaKbKb
Sekitori-No.-120: C. gr1gr1gr2gr2KaKaKbKb
where C indicates a fundamental gene-complex, and the genes Ka and Kb mainly govern the density of the grains in the panicle as were reported by Prof. Takezaki (1932).
(6) The genes Gr1, Gr2 and Ka likewise govern the length, breadth and width of the grain, the function of Gr1 and Gr2 bring accumulative and of inperfect dominance, while that of Ka is inhibitory and of perfect dominance. The qualifying effects of these genes on the three dimensions are multiplicative to the value of the fundamental gene-complex, as shown in the genes P1, H1, P2, P3 and Ka in the writer's previous reports (Syakudo, 1948-a, -b, 1949).
(7) The qualifying values of the genes for the three dimensions which were calculated with the Prof. Takezaki's least square method (Takezaki, 1927) are as follows:-
The difference of the qualifying values in the two years is probably due to the difference of the environmental conditions.
(8) The gene for the grain length Gr1 and the gene for the panicle length P2 (Syakudo, 1948) seem to be the same one, while the gene for the grain length Gr2 and the gene for the panicle length P3 seem to be not the same, though Gr2 gives some effect on panicle length and P3 on grain length. Thus the effects of the genes which concern the quantitative characters are frequently pleiotropous.
(9) From these results a number of considerations necessary for plant-breeding works may be pointed out, on which the writer has already described in his previous report (Syakudo, 1949).
