Hybrid seed production requires a male sterile parent. Why?

Question

Hybridization is the process of crossing two plant species or varieties. In this case, two varieties of plants. In plant breeding, crossing is a very useful technique to improve the features of the offspring. For example, if a maize corn variety has lost yield over the years, it can be crossed to a variety with a higher yield and the offspring will also have a higher yield.

In order to cross these two varieties, the male needs to be sterile. Why is that? I don't understand how the process works and I cannot find the reason anywhere. The answer should be pretty basic, and I think I am missing something that everybody assumes I should know.

Answer 1

male-sterility is not required for breeding.

Male-sterility means that the female acting plant (the plant that will bear the fruit) has sterile male organs (either dysfunctional anthers or sterile pollen). and won't self pollinate. The male-acting plant is fertile.

In monoecious plants this is helpful for breeding because we can't easily provide a controlled pollinating environment by separating the female and male organs

Tomatoes are monoecious (hermaphrodites), self-pollinated. The pollination occurs (usually) before the flower opens. Male-sterility prevents pollination and allows the breeder to pollinate.

Corn is a cross-pollinated plant with some capacity for self-pollination, male-sterility in corn helps ensure that the corn plant is not pollinated by itself.

Male-sterility gives peace of mind and easier breeding techniques but is not a requirement.

You can expand your knowledge using Principles of Plant Genetics and Breeding, Second Edition by George Acquaah. Check chapters 5: Introduction to Reproduction and Autogamy. Searching "male sterility in plants explained" in google yielded many relevant pdfs.

Answer 2

To get a hybrid you need pollen from a different plant. Corn is likely to self-pollinate if some action is not taken to prevent it. I don't know of sterile males plants - in the US corn belt the self-pollination is prevented by detasseling. Many young people get summer jobs detasseling (cutting off the tassels) for seed corn.