Cytoplasmic restoration of nuclear genetic male sterility
Hermsen (1968, Euphytica Sup. No. 1:63-67), discussed a system which would utilize a nuclear gene pair for fertility vs. male sterility (Ms* vs. ms*), together with a type of cytoplasm that would restore fertility to a genotype homozygous recessive at the ms* locus. No examples were cited. One of the advantages of such a system, as discussed by Washnok (1972, MGNL 46:25-27) is that the ultimate hybrid planted by the farmer would have normal cytoplasm. The purpose of this note is to call attention to the manner in which such a system was discovered in flax. Bateson and Gairdner (1921, J. Gen. 11:269) and Gairdner (1929, J. Gen. 21:117-124) reported that crosses using a procumbent strain as female with tall strains as male had fertile F1's but segregated 3 fertile:1 male sterile in F2. Progeny of the reciprocal crosses were all fertile in F1 and F2. The explanation offered was that the tall strains were homozygous for a recessive ms* gene but had a type of cytoplasm that made them fertile; the procumbent strain had the normal Ms* gene but a type of cytoplasm which, with an ms* ms* genotype, produced a male-sterile plant. We propose the usage of (R) for the restorer cytoplasm and (r) for the non-restorer cytoplasm. The procumbent strain would be (R) ms* ms* and the tall strain (r) Ms* Ms*.
During studies of the inheritance of wilt resistance in flax, a large-seeded Crete variety behaved in a manner similar to that of the procumbent strain (Burnham, Ph.D. thesis, Univ. of Wisc.). Only by the study of reciprocal crosses carried into F2 was the system discovered in flax. A paper reporting results of crosses with the Crete variety of flax and outlining a system for using cytoplasmic restoration of nuclear genetic male sterility is in its final stages of preparation: Burnham, C. R., M. C. Albertsen, and R. L. Phillips, Cytoplasmic restoration of nuclear genetic male sterility.
For a similar test for such a system in corn, reciprocal dialleles within groups of inbreds in corn (7, 6, and 6 inbreds in each of three groups) are being checked in F2 for segregation for male sterility. F2's for all the crosses will be grown in 1978.
Charles R. Burnham
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