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Wednesday - January 30, 2008

From: Austin, TX
Region: Southwest
Topic: Trees
Title: Determination of the sex of Mexican persimmon (Diospyros texana)
Answered by: Nan Hampton

QUESTION:

Last spring, I planted a persimmon fruit from a Mexican Persimmon. I now have 6 small seedlings coming up. Since they all came from the same seed source - 1 black persimmon, will they all be male trees (or all be female trees)?

ANSWER:

Most plants (around 90%) are hermaphroditic. In other words, they have flowers that are "perfect" with both stamens (the male structure that produces pollen) and pistils (the female structure that contains the ovule that, after fertilization by the pollen, is the fruit with the seeds that grow into the next generation of plants). A small number of plants (around 10%) produce separate staminate (male) flowers and pistillate (female) flowers. Sometimes these separate flowers are found on the same plant (as in Zea mays, corn or maize). Such plants are called monoecious (from the Greek for "one house"). When the male flowers and female flowers are found on separate plants they are dioecious (from, as you might have anticipated, the Greek for "two houses"). This is the situation for Diospyros texana (Texas persimmon). There are variations/combinations of these three scenarios that I won't go into here, but you can click here to learn more than you probably want to know about plant sexuality or you can read: Tanurdzic, M. and J. A. Banks. 2004. Sex-Determining Mechanisms in Land Plants. Plant Cell 16:S61-S71.

Although for the majority of plants (the hermaphroditic ones) sex determination is not a consideration, how is sex determined for the monoecious and the dioecious ones? As it turns out, there are several different strategies and all are genetic. In monoecious plants the incipient flowers begin with both pistlls and stamens but the sex determination genes (usually several different genes) cause the arrested development of the pistils in the male flower and the stamens in the female flowers. The level of gibberellin (a plant hormone) appears to be important in determining which type flower (staminate—male or pistillate—female) is produced. Exactly how it does this is not yet precisely known.

Some, but not all, dioecious plants have one pair of chromosomes that are not identical that are associated with determining the sex of the individual plant. This resembles the situation in mammals where males are XY and females are XX. For instance, Silene latifolia (bladder campion) has 24 chromosomes per cell. Twenty-two of these are autosomes (non-sex chromosomes) but two of these are sex chromosomes with XX individuals making female flowers and XY having male flowers. Other dioecious plants don't have a pair of visibly different chromosomes, but that doesn't necessarily mean that one pair of chromosomes might not be the sex chromosomes.

So, now for the answer to your specific question as to whether the plants from your one fruit will be all females or all males—I don't know for sure, but I suspect it will a mixture of males and females.

First, I could find no information about whether D. texana has visible sex chromosomes. I only know that it is dioecious. If it does have sex chromosomes, the female tree that produced the fruit had ovules with one X chromosome and the male tree that produced the pollen would have pollen grains with either an X or a Y. It would depend on which type of pollen grain (with either an X or a Y) fertilized the ovule as to whether the resulting plant would be female (XX) or male (XY). Each of the seeds in the fruit you planted would have been fertilized by a different pollen grain. Assuming that pollination is random, it isn't likely that your six seedlings are all males or all females.