Inheritance of Male Sterility in Flax Involving Nuclear‐Cytoplasmic Interaction, Including Methods of Testing for Cytoplasmic Restoration1

Abstract

An interaction between cytoplasm and nuclear genes affecting the inheritance of male sterility in flax (Linum usitatissimum L.) was reported first by workers in England in the 1920s in crosses between procumbent and tall plants and later by a worker in Poland using Linum floccosum. Previously unpublished data are reported on a similar case involving a large‐seeded flax from Crete. The interaction was discovered in all cases by noting that crosses using procumbent, L. floccosum, and Crete as female parents with most other stocks as male parents had fertile and male‐sterile plants in F2; whereas the reciprocal crosses had only fertile plants.For certain crosses using Crete as the female parent, the F2 segregation ratios were for a single gene difference. Other crosses may have involved two genes complementary either for restoration of pollen fertility in F1 or for incomplete restoration. Either of two hypotheses will explain the difference in behavior between reciprocal crosses. One hypothesis is that procumbent, L. floccosum, and Crete have a dominant fertility allele, Ms, and a non‐restorer [N] cytoplasm. Most other stocks have the recessive male‐sterile, ms ms, nuclear genotype but a cytoplasm [c R] that restores fertility. The cross of male steriles [N] ms ms with maintainer [c R] ms ms stocks would produce all male‐sterile progeny. Crossing these male steriles with Ms Ms would produce hybrid seed.The second hypothesis that may explain the difference in behavior between reciprocal crosses assumes that procumbent, L. floccosum, and Crete have cytoplasmic male sterility [cms] together with a nuclear gene for restoration of pollen fertility (Rf). Most other flax stocks would have a normal non‐male‐sterile cytoplasm [N] and the non‐restorer gene, rf. Male‐sterile plants would be [cms] rf rf and maintainer stocks would be [N] rf rf.Tests using genetic male sterility to identify lines with cytoplasmic restoration of fertility are discussed, together with methods of distinguishing the possible nuclear genotypes.For any species in which most stocks have the nonrestorer [N] type of cytoplasm and the restorer type [c R] is rare, an advantage of this system for producing hybrid seed is the ability to produce large quantities of seed that will give only male‐sterile plants yet not transmit a unique cytoplasm to the hybrid seed offered to farmers. Development and maintenance of the parental stocks can be accomplished by conventional breeding techniques.