Semi-lethality in hybrid offspring of wheat

Summary Seven of the wheat crosses which were performed in 1954 and 1955 produced a uniform semi-lethal F₁. Among these were four combinations with the spring wheat Koga and two with the Turkish winter wheat Eskischir. The degree of withering in the F₁ appeared to be dependent on the variety with which Koga or Eskischir were combined. In the F₂ of the Koga crosses carried out in 1954 a 9 : 7 ratio of semi-lethals and normal plants was found. The almost continuous gradation in semi-lethality within the group of semi-lethal plants of every F₂ was conspicuous.The facts are explained as follows: Two complementary genes determine the semi-lethality as such, while modifying genes are responsible for the different degrees of semi-lethality of the different F₁'s and for the variation in degree of semi-lethality within every F₂. In the discussion this explanation is given in detail.It is pointed out that it is perhaps possible, with the aid of the phenomenon of semi-lethality, to discover or confirm relationships between species and/or varieties.Finally it is suggested that the rejection of F₁'s with withering symptoms is premature.