During discussions of the usefulness of cytoplasmic restoration of fertility to nuclear genetic male sterility by Phillips and Albertsen, attention was directed to reports of male sterility in flax governed by an interaction between cytoplasm and nuclear genes. The first report was by Bateson and Gairdner in 1921. A procumbent strain, when used as the female parent with other varieties, segregated for male sterility in F2, but reciprocal crosses did not segregate. I found the same behavior for most crosses involving a variety from Crete, reported only briefly in my "Discussions in Cytogenetics." Although not recognized as possible examples of cytoplasmic restoration of fertility, the explanations used were essentially that. I thought it was a possible example until Dr. Phillips suggested that cytoplasmic male sterility interacting with restorer genes, the explanation used in corn, might fit the breeding results in flax also.

Assume: (c ms), (R), and (N) represent cytoplasmic male sterility, restorer cytoplasm, and normal (non-restorer) cytoplasm respectively. One possible explanation for the breeding behavior in flax is that a nuclear gene for male sterility (ms) is restored to fertility by a restorer (R) cytoplasm. On this hypothesis, procumbent and Crete are (N) Ms Ms and most other varieties are (R) ms ms.

The alternative explanation is: cytoplasmic male sterility (c ms) interacting with nuclear restorer vs. non-restorer genes, Rf vs. rf. On this hypothesis, the procumbent and Crete varieties of flax are (c ms) Rf Rf and most others are (N) rf rf. Either explanation will fit the results in flax. A paper is being

prepared for Crop Science by myself, Albertsen and Phillips reporting data on the behavior of Crete and other varieties in flax and the kinds of tests needed to establish firmly a case of cytoplasmic restoration of fertility.

Charles R. Burnham

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