I have often seen descriptions of certain fruit trees, specified as self fertile, that their productivity can be increased by having two or more trees of the same variety nearby. I can't understand what is the genetic difference between pollen from the same tree and pollen from an identical species nearby. Is there some other mechanism at work here?
Sherwin Dubren
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Hey Sherwin,
Basically, you and your wife (or ex-girlfriend, potential mate, etc.) are of the same species. But you clearly still have genetic differences (assuming you don't have a "domestic partnership" with an identifcal twin).
Generally, offspring with more genetic diversity do better due to a phenomenom called inbreeding depression.
However, plants are a little more crazy in their mating requirements than humans (maybe it has to do with being rooted in one spot?). Plants can fertilize themselves within the same flower, they can swap pollen between flowers on the same plant, they can swap pollen between clones, and they can swap pollen between two genetically different plants (out-crossing - like human mating).
For most organisms, out-crossing leads to greater offspring success. More genetic diversity leads to better ability to adapt to environments. Think of the few health problems with mutt dogs compared to the breed specific health problems of pure bred dogs.
The same is true of the trees. My guess is that the trees can self-fertilize, but they usually have some sort of inbreeding depression. This means you get less fruit if your trees are selfing than if they are being fertilized by other species.
~becca
Hi Sherwin, I just read Becca's reply and I have some problems with her answer, especially that last paragraph. I think both of you are being a little careless with the use of the word "species". All peaches, for example, are the same species. In the wild, plants cross pollinate with other (often genetically slightly different) members of the same species. Sure, there are natural hybrids, but those are really mistakes of nature. We humans have selected (or created by selective breeding) the best of the species, which we propagate, usually by grafting. If you have two golden delicious trees standing side by side, they are, for all practical purposes, the same exact tree. There is more than one species of plum and the two main species do not pollinate each other. European plums are quite self fertile but Japanese plums, as I recall, are not. All apple cultivars, generally, can cross pollinate with the other cultivars. One exception would occur if you had one that bloomed very early and a second that bloomed very late. They would just miss each other. The other exception that comes to mind is the fact that some apple cultivars are triploids and produce sterile pollen. They can't pollinate anything, not even themselves.
OK, let me finally get to the heart of your question. Let's say you want to grow a Stanley Plum or a Redhaven peach. Both are fairly self fertile. If your catalog says to plant two of the same cultivar for even better pollination, they are just trying to sell more trees! They might be right if they recommended a different European plum or a different peach, since then there could be some improvement.
The only possible mechanism that I can think of that could make two identical trees pollinate better than one is as follows. Suppose you had an Elberta peach and it was the only fruit tree for a mile in any direction. If you had another Elberta growing next to it, there would be twice as many flowers and just maybe that would attract more bees. More bees would pollinate more flowers and might improve fruit set. That's a bit of a stretch and it would only matter if your area had a low bee population.
Steve
Sherw> I have often seen descriptions of certain fruit trees, specified as self
Well, I don't know. Maybe there's something going on that I haven't thought of. One thing to keep in mind is that there are varieties of fruit that are really seed grown. They wouldn't be genetically identical but so similar that people consider them a variety. I really don't think Moorpark Apricot fits in that category. I'm almost certain that it is a grafted cultivar with all Moorparks identical to the original tree. Another possibility to keep in mind is that people often repeat common knowledge that isn't really true. You can bet the person who wrote the Moorpark Apricot part of your book didn't do the research himself. He probably read that fact several times in the past and believes it to be true. Maybe it IS true but maybe not. My favorite example of this is about poinsettias being poisonous. Long ago, a child in Hawaii ate a poinsettia leaf and then died. For over fifty years, everyone just knew that poinsettias are poisonous. Only in recent years did someone actually test the idea and find a person can eat the plant and not be poisoned.
Let me locate a web site about this because someone who reads this probably still thinks poinsettias are poisonous. Here we go:
Sherw> Hi Steve,
Just speculating here. Taking up one thread from Steve:
My recollection is that during that short period of their lives when honey bees are gathering, a given bee will specialize in a given type of blossom. (This might make sense from a data storage point of view, tiny brain, figures out 1 type of blossom, etc.) So if this is the case, if there were twice as many peach trees, (2 instead of 1) there would be twice the chance that a newbee would first encounter a peach and then specialize in it doubling the number of peach tree bees and doubling the chance of both peach trees being fertilized. Although perhaps each with its own pollen.
Maybee? David.
Steve wrote: .......
Hi All, honey bees will go for for the largest area of polination, because they are after the volume of nectar. so if you have a couple of trees, next to a field of oil seed rape, they may very well ignore your trees in favour of the rape. it is easy for bees to work a large area, rather than go from tree to tree and waste time. hope this makes sense and is of some help to you.
bleh! I'm just jamming along on the species vibe, while totally ignoring the grafting aspect. I don't know what to tell you about that...
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