Cytoplasmic male sterility (CMS) is used in hybrid seed production. Usually three kinds of lines are needed in this breeding program:
1. Male-sterile line.
2. Maintainer line. The male-sterile line is maintained by crossing with a 'maintainer line'. So you can have the male-sterile seeds/plants ready for use.
3. Restorer line. 'Restorer line' is used to cross male-sterile line to produce hybrid seeds.
3. See attached pictures (B line = Maintainer line; R line = Restorer line).
Cytoplasmic male sterility is used in hybrid seed production. ... These CMS lines must be maintained by repeated crossing to a sister line (known as the maintainer line) that is genetically identical except that it possesses normal cytoplasm and is therefore male-fertile.
Transfer of CMS from one line to another:
"CMS may be transferred easily to a given strain by using that strain as a pollinator (recurrent parent) in the successive generation of backcross program. After 6-7 backcrosses the nuclear genotype of male sterile line would be almost identical to that of the recurrent pollinator strain. The male sterile line is maintained by crossing it with pollinator strain used as a recurrent parent in backcross, since the nuclear genotype of the pollinator is identical with that of the new male sterile line. Such a male fertile line is known as maintainer line or ‘B’ line and male sterile line is also known as ‘A' line."
(http://agriinfo.in/default.aspx?page=topic&superid=3&topicid=1776)
Commercial production of CMS rice for example (see attached picture, right panel, 3-line production).
Hybrid seed production using Cytoplasmic Male Sterility (CMS) is based on three line system i.e. A, B and R line.
A-line: CMS line is called as A line. This is sterile due to the genes in cytoplasm (mitochondrial DNA).
B-line: This is isogenic (genotypically identical except one gene) to CMS line except fertility. It maintains A line. It means if you want seed of A line, you have to cross it with B line otherwise A line will be no more as it has no active male parts.
R line: This line has restorer genes in nucleus to restore fertility of A line. R line is entirely different to that A and B line. R line has very high SCA (Specific Combining Ability) effects. It is used to produce hybrid seeds
see again:
A x A = No seed
B x B = B line seed
R x R = R line seed
A x B = A line seed
A x R = Hybrid seed
regards
@ Rasi Hamid,
The roles of Maintainer and Restorer lines in cytoplasm genetic male sterility (CGMS, your question) and cytoplasm male sterility (CMS) breeding system are similar. Please see the slide presentation (slides #19-25) regarding using CGMS in Pearl millet hybrid breeding. [ http://www.slideshare.net/dipti1121/pearlmillet-heterosis-and-hybrid-seed-production ].
Slide #24 has a mistake, it should be '4:1/6:2 A&R rows', not A&B.
Role of Maintainer line (B-line): To maintain the A-line i.e. MS line. A x B= Continuous availability of MS seeds and now these seeds can be utilized for crossing with R line for hybrid seed production
MS line(A) x R = Hybrid seeds
Hope you are clear now.
Maintainer line( B ) line maintains the sterility of the CMS (A) line and is used to produce the seed of the CMS line by crossing A x B lines.Restorer line (R) line on the other hand carries fertility restorer genes and therefore restores the fertility upon crossing with CMS A line
Line B is maintainer for Line A.
Rf line is restorer line , Rf x A = Hybrid seed.
Rasmieh Hamid
I have attached a detailed review of CMS systems in crop plants. Go Through it for understanding.
Article Male Sterility and Fertility Restoration in Crops
Maintainer line (B line) maintains the male sterile line (A line) by pollinating and to get seeds ,,where as R line is used for hybrid seed production through hybridization ie A x R crossing
In case of cytoplasmic male sterility systen, the Maintainer line known as B-line is used to maintain Male sterile line-A, while Restorer line known as R-line restores fertility of Male sterile line-A. Line-A and Line-R are crossed together to produce hybrid seed.
R-line is a male fertile line used as pollen parent in commercial seed production plot. Test cross programmes help identify maintainers as well as restorers. Maintainer lines used for conversion into new CMS lines and restorer lines are subsequently used as male parent in hybrid development programme.
In Commercial sorghum hybrid seed production, cytoplasmic male sterility system is used as compared to maize where, the Maintainer line known as B-line is used to maintain Male sterile line-A, while Restorer line known as R-line restores fertility of Male sterile line-A. Line-A and Line-R are crossed together to produce hybrid seed.
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