The degree of semisterility of a maize stock with a heterozygous translocation (N/T) is difficult to estimate when the kernels are fully mature. This is because each well-developed kernel may occupy the space of two embedded ovaries where one fertilized ovary has aborted. In the early stages of ear development, 2 weeks following pollination, the semisterility (%) of an N/T maize-ear could be easily determined. This is because the functional fertilized ovary or the zygote only occupies one ovary position at this stage. However, this method of estimating has the disadvantage of sacrificing a maize ear before the ear reaches maturity.

In order to overcome this difficulty and avoid sacrificing the mature ear, we have adopted an alternative method. First, we have assumed that:

Semisterility (%) = total no. of developed kernels               X 100
                               no. of ovaries per row x no. of rows

The total number of developed kernels and number of rows per examined ear is recorded. In order to determine the number of ovaries per row, the kernels of two or three rows from different areas of an examined ear are removed. Then, this kernel-less cob area is scraped with a scalpel to expose the cupules (Galinat, 1956, Botanical Museum Leaflets 17:221). This process reveals the site of each ovary attachment. The numbers and types (either fertile or aborted zygotes) of ovaries per row are obtained by averaging the number of ovaries in these two or three rows.

It was found that the functional fertilized ovary or zygote is embedded much deeper on the cob than those that are aborted.

Sun-Yuan Hsu and Peter A. Peterson

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