E-mail Ques. Determining seed sex

Doctor Myers,
My question is when is a seeds sex determined? Is it genetically predetermined when
the seed is created, or do environmental factors play a part? Thank you
and htg supply for some really interesting and well written articles
and hopefully the answer to my question-

A. This is a great question but there is no one definitive scientific answer (good question!). Your question of course suggests you are growing a dioecious plant species, one that has separate male and female plants. Most plants have both male and female flowers on the same plant. Many plants seem to have a predetermined sex at fertilization, (This means seed sex is determined at germination for many plants) but this is not always the case. Most scientists think that having separate male and female plants has evolved several times in flowering plants. This means there may be differences in how sex is determined in a seed.
To give you more of a helpful answer, there is some specific research on the subject of sex determination. It was found that the amount of fertilizing pollen can influence the sex ratio (number of males vs. females) in dioecious plants. It was found an increase in pollen amount leads to decrease in number of male plants in the progeny. This relationship was confirmed on three plant species from three families – Rumex acetosa (Polygonaceae), Melandrium album (Cariophyllaceae), and Humulus japonicus (Cannabinaceae). If you are interested in female plants, you should then use a lot of pollen when breeding. This idea of more females occurring when there is a lot of pollen during fertilization is logical evolutionarily too. If there is a lot of pollen it means there is a lot of males in the population. Therefore, it would be better to have female offspring since having a male offspring would mean it had to compete with a lot of other males. Plants that had this genetic trait (making females when there is a lot of pollen produced by males) would be successful since all their daughters would be pollinated and would pass on their genes, the mechanism of natural selection.
Other factors like temperature, light and water may have an effect on the number of males and females that come from a group seeds, however this is going to be different from one species to the next. The truth is there is a lot to learn in this area of plant growing and your question is right on the edge of scientific unerstanding. Thanks for your question!

Good Growing,
Dr. E. R Myers

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