| The Terminology Committee recommends the above symbols for cytoplasmic
male - sterility in corn, but also that a different set of symbols be used
to designate a different cytoplasm. In the preparation of the statement on cytoplasmic male - sterile terminology in corn, the Committee wishes to acknowledge the assistance of: (a) Donald N. DUVICK, Pionier Hi - Bred Corn Company, Johnston, Iowa. (b) G. F. SPRAGUE, Leader, Corn and Sorghum Investigations, Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Maryland. Sorghums (Sorghum vulgare PERS.) At the present time, only one cytoplasmic male - sterility system is used in the commercial production of hybrid sorghum seed. It was discovered through the introduction of kafir chromosomes into milo cytoplasm. The male sterility is caused by an interaction between male - sterility - inducing cytoplasm and specific nuclear genes. Male fertility as well as male sterility in the sterilityinducing cytoplasm are controlled by a single factor pair designated Msc msc. The homozygous (Msc Msc) or heterozygous (Msc msc) dominants produce pollen fertility, whereas the homozygous recessives (msc msc) produce male sterility. The F2 generation segregates 3 fertile to 1 male - sterile. A wide range of partial fertility occurs in the pollen - fertile (Msc) class as a result of inter - allelic and intra - allelic interactions of two factor pairs designated Pf1 pf1 Pf2 pf2. The lowest pollen fertility (5 - 10 %), as determined by percentage of stained pollen, is found in the double - recessive genotype, pf1 pf1 pf2 pf2. The homozygous dominants, Pf1 Pf1 Pf2 Pf2, have approximately 90 % of stained pollen. Sorghum breeders use the practical terms A, B, and R for pertinent lines used in the production of sorghum hybrids. The A line designates the cytoplasmic male - sterile line, produced by crosses of a given line into male - sterility - inducing cytoplasm followed by successive backcrosses to the given line. Genetically, it is msc msc in male - sterility - inducing cytoplasm. In seed - production fields, it is generally called the seed parent. The sterility - maintainer is called the B line. It is a pollen - fertile line that has been used to produce a cytoplasmic male - sterile (A line) counterpart by recurrent backcrosses. Genetically, the B line msc msc in normal or fertility - inducing cytoplasm. The fertility - restorer line is the R line that is fertile in sterility - inducing cytoplasm, or that produces normal pollen fertility in the F1 of a cross with a cytoplasmic male - sterile line. Genetically, the R - restorer line is MscMsc. In seed - production fields, it is generally called the pollen parent. Some breeders, but particularly hybrid seed producers, use the letter designations with variety names, e.g., A - Martin and B - Martin. More frequently they are used with serial numbers, as A - 398 and B - 398 for male - sterile and male - fertile Martin, respectively. The R designation is generally used with a serial number, as R - 7005 for the fertility - restorer variety Plainsman. |
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