A large program of conversion to genic male sterility was initiated in 1972 using 26 widely used public corn inbreds. By 1977, only three of the original inbreds had been successfully converted: W64A, W117 and A619. Difficulties were encountered with the duplicate-deficient maintainer versions of the remaining 23 inbreds. Maintainer plants were all extremely late, short and extremely poor pollen shedders. Sterile plants obtained showed less than 0.1% fertility, but increase of the steriles was virtually impossible due to the poor pollen shed of the maintainer plants. The T9-10a translocation, coupled with the ms2 gene, was successfully used in the conversion of W64A, W117 and A619.
Miniature seed fields were grown in 1977 to determine the economic feasibility of using the system. One isolation field grown near Eldora, Iowa, consisted of W64A sterile and maintainer rows in a four to two ratio. Another isolation in the area contained A619 sterile and maintainer rows in a similar ratio. Under drought stress conditions, both fields produced female yields of less than one bushel per acre. Conventional detasseled seed fields in the immediate area yielded 15-20 bushels per acre.
Similar seed fields of W64A and W117 were grown under more optimum moisture
conditions near Olivia, Minnesota in 1977. Yield data are shown below:
|Genotype||Range, % water||Range, Yield, Bu/A|
The W117 field produced only scattered kernels and was abandoned. Seed fields of W64A in normal cytoplasm produced yields ranging from 30 to 55 bushels per acre in the immediate area in 1977.
This project was discontinued for the following reasons:
1. Yields of female and male plantings were extremely low in 1977 despite optimum growing conditions and an excellent pollination period.
2. Extremely high foundation seed production costs would more than offset the amount of detasseling costs in this system.
3. Increasing and maintaining male seed is extremely time consuming.
4. Due to the length of time involved in conversion, inbred lines can become outdated before conversion is completed.
5. Personal communication with other plant breeders indicates much difficulty with the conversion programs.
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