In case of finding new restorer loci, is it necessary to develop new CMS line? Or one can use existing CMS line and cross with different inbred lines to establish a CMS system?
When looking at cytoplasmic inheritance the genes that confer the male sterility are situated in the mitochrondria of the cell. The are replicated from the female parent. In crops with this trait the lines with the male sterility can be used as functional females in the cross or hybrid.
To make hybrid lines are identified that have nuclear genes that restore male fertility the so called restorer or R lines. In a breeding lines R lines c lines and m lines would be keep separately.
The lines that propagate the male sterile lines but can be used to keep the inbred lines going are called maintainer lines M lines.
Once male sterile c lines are found and the m lines for maintenance. The key will be to find the racial parentage that give heterosis or hybrid vigor. Restorer lines will be crossed to superior c lines to find the best alternatives for a commercialized hybrid.
After the different reactions are made clear you immediate goal will be find the heterosis patterns which is critical for hybrid vigor. Single male restorer lines can be crossed against many female male cytoplasmic lines and planted in row trials to determine those that might have superior reaction. In seed companies the use of tropical off season nurseries advances the development and testing of these lines giving superior results in a shortened time frame.