抄録
Based on three facts, i.e., (1) three common wheats, Prelude, Jones Fife and Macha form a necrosis triangle, (2) a 27:37 segregation ratio of necrotic vs. normal plants was obtained in the F2 generation of the cross, Chinese Spring x Macha, and (3) three genes, Ne1, Ne2 and Ne3, were located in different chromosomes, Tsunewaki and Kihara (1962) proposed a three gene hypothesis for necrosis, for whose appearance the genes Ne1, Ne2 and Ne3 were assumed to be necessary.
In order to work out further proofs for this hypothesis, two experiments were carried out. In the first experiment, Macha was crossed to Chinese Spring monosomics and the phenotypes of the F1 plants in relation to their chromosome numbers were studied. In the second experiment, F2, F3 and some F4 hybrids of the cross, Chinese Spring mono-3D x Macha, were studied by test-crossing them to Prelude, Jones Fife and Macha.
Against the expectation, the following results were obtained, that disproved the three gene hypothesis;
(1) Chinese Spring carries a single complementary gene, Ch2, for chlorosis on chromosome 3D (formerly XVI).
(2) Macha carries a necrosis gene, Ne1, and a chlorosis gene, Ch1. However, it does not possess the other necrosis gene, Ne2.
From these results, it was concluded that necrosis (formerly, the epidemic type of necrosis) and chlorosis (formerly, its systemic type) are under control of two independent gene systems, each consisting of two complementary genes; necrosis is determined by Ne1 and Ne2, and chlorosis by Ch1 and Ch2 (formerly Ne3).
Genic as well as phenotypic relationship between the formerly proposed and the present system is diagrammed in Fig. 2. Furthermore, a single-gene and two-gene tester series were compared in relation to their efficiency for differentiating the nine possible genotypes for necrosis and chlorosis. It is concluded that the two-gene tester series is, at present, more efficient than the one-gene series.
