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?
Due to Google delay this post may show up long after better & more
relevant statements have been made.
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
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.
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
Sherwin Dubren wrote:
You are correct about my misuse of the term species. I meant to say
cultivar. However, I think there might be more going on here than just
companies trying to sell more trees. If you look in the 'Fruit, Berry
Nut Inventory' book, you will find occasional references to this
recommendation to plant more trees. This book is put out by Seed Savers
Exchange, but I doubt if they directly or indirectly profit from the
of the trees cataloged in their book. You can check the latest Third
Edition. An example would be the Moorpark Apricot on page 188 where I
quote 'Self-fertile, but fruit set is increased by planting two or
Your reasoning in the last paragraph of your message would really be
of any fruit tree which is considered self-fertile, yet the inventory
only mentions this phenomenon for specific cultivars.
Well, I don't know. Maybe there's something going on that I haven't
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:
Sherwin Dubren wrote:
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.
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.
Richard M. Watkin.
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