Inheritance and Linkage Studies of Cytoplasmic Male Sterility and Monogermity in Sugar Beets

Abstract

Annual multigerm and monogerm pollen restorer lines (P-MM and P-mm), which, were isolated from the cross combination of the annual multigerm (cytoplasmic) male sterile and biennial monogerm strain both introduced from USA, were crossed with annual multigerm and monogerm male sterile lines (TA-1-MS and TA-2-MS). F₁ and F₂ populations of the cross combination of TA-2-MSXP-mm and TA-1-MSXP-MM were grown and checked for two characters, male sterility and monogermity, at the Yamagata University (Tsuruoka) during the summer of 1972, 1973 and 1974. This study confirmed that monogermity was governed by recessive monogenic inheritance, although monogerm plants in F₂ Segregation were slightly fewer than the expected value. Pollen parent lines and F₁ populations segregated no complete sterile plants, but considerably produced semisterile plants besides complete fertile plants. The appearance of semi-sterile types was attributable to effects of environment and minor modifying genes in the interaction with two major genes. The mode of inheritance applied to the pollen parent lines used in this study was as follows : Using the Owen's gene scheme, complete sterility and semi-sterility are governed by only X gene locus and complete sterility is induced by the single recessive condition, whereas pollen fertility is controlled by the complementary effect of X and Z genes. This will support Owen's original hypothesis. In addition to this gene scheme, minor modifying genes accelarate or suppress male sterility. Linkage relation between one pollen restorer gene, X, and monogerm gene was not recognized in this cross combinations. In linkage relation between the other pollen restorer gene, Z, and monogerm gene, there were some cases of the significant inter-action between the two genes, which was responsible for segregations as if the F₂ had been in a coupling phase of linkage notwithstanding a repulsion phase. This suggests that Z gene locus was independent of monogerm gene.