Objective - To increase the quantity and quality of hybrid seed corn production by use of cytogenetic phenomena. Donor inbreds are developed whose chromosomes function in hybrid plant development (sporophyte) but do not take part in seed development (gametophyte). This results in single cross hybrid seed production on a vigorous hybrid plant instead of on a weak inbred plant.
Background - Mitosis, the process of nuclear division that accompanies plant growth, differs from meiosis, where the chromosome complement is reduced from diploid (2n) to haploid (n) to form gametes. The intent is to take advantage of natural differences between these two processes or to take advantage of an unusual genetic or cytological control of chromosomes in these two processes to cause chromosomes from a donor inbred to take part in mitosis but not in meiosis.
Definitions - Female inbred is a normal inbred that is used as the female in conventional production fields of a commercial hybrid. Male inbred is a normal inbred that is used as the male in production fields of a commercial hybrid. Donor inbred is a corn inbred that contains an unusual genetic or cytological entity that controls its own genome function when in hybrid combination with a normal inbred so that its chromosome complement will be included in mitosis but not be included in meiosis.
Procedure - First generation, the foundation seed is produced. The donor inbred is crossed with the female inbred; the donor inbred is used as a female to incorporate cytoplasmic male sterility. A series of donor inbreds of different flowering date will allow the particular female cross chosen to silk at the proper time to receive the pollen of the male inbred in the production field. Second generation, the production field is grown. The donor inbred times female inbred seedstock is grown as the female. The male inbred seedstock is grown as the male. Both seedstocks are planted at the same time and detasseling is not necessary in the sterile portion of the field. The single cross hybrid seed that is to be sold to the farmer is harvested from the hybrid female in the usual way.
Advantages - Seed yields are increased. Seed quality is improved. Same-time planting of male and female in production fields is achieved. Fewer seedstocks for sterile conversion are necessary in foundation seed.
A. Forrest Troyer
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