Pollination - monoecious/dioecious, same species, different varieties. Confused!

Hi everyone,

My main post is here https://permies.com/t/40/154597/Garden-Scratch-ADVICE#1327139, but this question is quite specific so thought it might be more relevant in this forum.

I'm choosing plants for my garden and am getting confused about pollination. Are dioecious plants either male or female and pollinate each other even when they are the same variety? I've also ready about plants which need to be pollinated by a different variety of the same species but I don't know how this fits in with the monoecious/dioecious distinction. The male/female aspect of dioecious plants makes sense to me, but I don't understand why a plant would need to be pollinated by a different variety of the same species? Is it nature's way of promoting genetic diversity? If you like the variety that you already have and want to keep seeds from the plant, how could you get seeds of the same variety if it always needs to be pollinated by a different variety (and therefore creating seeds with genes from two different varieties)?

I read that the 'Limelight' variety of elaeagnus x ebbingei is a good pollinator for the species - but does it work both ways (i.e. they pollinate each other)? Would a goumi plant (elaeagnus multiflora) pollinate or be pollinated by the ebbingei's or does it not work because they are a different species (they are the same genus but I don't know if that's close enough for pollination)?

Getting quite confused, please help :)

Really good question G Prentice, and I hope someone with a bit more genetics knowledge can answer.
I know some monoecious plants have male and female parts which ripen at different times so cannot usually fertilse themselves - I have been doing a bit of research into walnuts which are one example of that. But apples for example are sometimes self fertile and sometimes they need a pollinating partner (complicated by the apple varieties blooming at different times).  
I suspect the answer is quite complex, but hopefully someone can put in laymans terms for us!

A plant like say kiwi is dioecious and there is a male plant it doesn't have ovaries and thus cant have fruits/babies and but it can can pollinate around 8 female plants.

There are dioecious plants that have both sperm/pollen and also ovaries, but when it produces pollen, it's ovaries don't work. So it can never fertilize itself. So you would have to get another cultivar.

Then there are cultivars that ripen earlier that other and they also blossom earlier than others, so because one plant blossom in April and the other in May, they can never fertilize each other, but if you were to somehow trap and preserve some of the pollen and then use your hand/brush/etc to transfer the pollen, then you could technically get them to fertilize each other.

Then you have some specific cultivars that only produce sterile pollen due to some mutation that makes them have 3 sets of DNA (e.g. triploid apple) vs the usual two sets (diploid apple). So while they can have fruit they can never pollinate/fertilize any plant.

Then we have some cultivars that are partially self-fertile, the fruits aren't as sweet/flavorful/numerous/properly shaped as they could have been. Kind of like having a child with your own sibling and then finding out that the kid is handicap, if the kid even comes to term.

Then there are some plants that are self-fertile, and they can do it all by themself.

It is possible to get seedling/babies that have similar properties to the parents. We see this happen all the time with animals like dogs/cow/sheep/etc. Even though they aren't clones, and they might have slightly different color, etc they have enough in common to be considered the same breed/landrace/open-pollinated cultivar.  

Thank you! All comments welcome - I can see that it’s quite a complicated topic!

Dioeciousness (each plant being either male or female) is one method plants use to prevent self-pollination. Kiwis, persimmons, mulberries, and spinach usually work this way. If you plant something from seed, like spinach, half the population will be male and half will be female, so you only need one variety. Named fruit tree varieties, on the other hand, are clones. All clones of a variety have the same gender. You need a second (male) variety to pollinate your first (female) variety.

Outcrossing increases genetic diversity and is generally advantageous. Most plants have mechanisms that encourage it, even if they don't require it. Dioeciousness is one of these mechanisms; others have been discussed already in this thread. A plant might have its female and male parts active at different times, or space them apart from each other in the flower, or even have a genetic mechanism that causes it to reject its own pollen. If a plant like this is grown in isolation, it might set no crop or a poor crop. This is the general case for lots of fruit crops, especially in the family rosaceae: apples, pears, plums, cherries, almonds, etc. However, degree of self-compatibility varies by variety. Granny Smith, for example, is an apple that is relatively good at pollinating itself.

Degree of compatibility between two varieties also varies. Imagine, as S Bengi suggested, that you have a variety whose female parts are active in April, but it doesn't produce pollen until May. To pollinate it, you would want a variety that produces lots of pollen in April. This is what people mean when they say that, for example, a Dorsett apple tree is a good pollinator for an Anna. Dorsett produces pollen in such a way, and at such a time, that Anna sets a good crop near it. Depending on the plants, good pollination may or may not go both ways.

If a tree is said to be a good pollinator overall, it probably produces lots of viable pollen over a long period of time, so is highly compatible with many other trees. It might also have flowers that are very attractive to pollinating insects. Flowering crab apples are like this.

To answer your question about saving seeds: names are confusing! Open-pollinated seed (like for annual vegetables) keeps its name as long as it hasn't crossed with another variety. If you grow Noble Giant spinach by itself and save the seeds, that's still Noble Giant spinach. If it crosses with Bloomsdale Longstanding spinach, the plants that grow from those seeds are a hybrid, no longer Noble Giant. People sometimes name and sell hybrids like this (this is hybrid vegetable seed). Only the seeds that are the direct offspring of two open-pollinated varieties count as the named hybrid. If you save seeds from a hybrid, it loses its name and becomes a new, exciting breeding population.

Named varieties grown from cuttings are different. All plants with the same name are clones of one original plant. Take your Limelight oleaster, for example. If you saved seed from it (assuming this is even possible), the plants that grew would not be Limelight, regardless of whether or not it was self-pollinated. They would be interesting new plants with traits inherited from their parents.

As for your elaeagnus questions: I'm not sure! My guess is that the elaeagnus x ebbingei will pollinate each other (and they appear to be partially self-fertile, so there should be SOME crop either way), but not the elaeagnus multiflora (also partially self-fertile). Cross-species pollination is usually tricky. If it DID work, and you got viable seeds, the offspring would be a horticultural breakthrough!

Edit: Didn't realize until after posting how much I was just repeating what S Bengi said...sorry!

Thanks - very useful!

If a crab apple pollinated a Granny Smith, for example, the fruit produced is just Granny Smith in characteristics, the fruit isn’t affected by the crab apple (smaller size) etc. - is that correct? But if I were to collect the seed from the Granny Smith apples and grow trees from them, the characteristics of the apples on the new trees would be a mix of the granny smith and the crab apple - the apples might be of a size in between a Granny Smith apple and a crab apple?

Elaeagnus x ebbingei is a hybrid species, right? I find it a bit confusing that hybrids are given new names that don’t tell you who the parent species are - I.e. ‘ebbingei’. I found one web page that said the parent species are ‘ a cross between E. macrophylla and E. pungens (or perhaps E. x reflexa)’, but otherwise it wasn’t easy to find info’ about this hybrid, which seems strange given how common it is.

Anyway, I’ll keep reading about it. So much to learn!

J. Hunch wrote:Dioeciousness (each plant being either male or female) is one method plants use to prevent self-pollination. Kiwis, persimmons, mulberries, and spinach usually work this way. If you plant something from seed, like spinach, half the population will be male and half will be female, so you only need one variety. Named fruit tree varieties, on the other hand, are clones. All clones of a variety have the same gender. You need a second (male) variety to pollinate your first (female) variety.

Outcrossing increases genetic diversity and is generally advantageous. Most plants have mechanisms that encourage it, even if they don't require it. Dioeciousness is one of these mechanisms; others have been discussed already in this thread. A plant might have its female and male parts active at different times, or space them apart from each other in the flower, or even have a genetic mechanism that causes it to reject its own pollen. If a plant like this is grown in isolation, it might set no crop or a poor crop. This is the general case for lots of fruit crops, especially in the family rosaceae: apples, pears, plums, cherries, almonds, etc. However, degree of self-compatibility varies by variety. Granny Smith, for example, is an apple that is relatively good at pollinating itself.

Degree of compatibility between two varieties also varies. Imagine, as S Bengi suggested, that you have a variety whose female parts are active in April, but it doesn't produce pollen until May. To pollinate it, you would want a variety that produces lots of pollen in April. This is what people mean when they say that, for example, a Dorsett apple tree is a good pollinator for an Anna. Dorsett produces pollen in such a way, and at such a time, that Anna sets a good crop near it. Depending on the plants, good pollination may or may not go both ways.

If a tree is said to be a good pollinator overall, it probably produces lots of viable pollen over a long period of time, so is highly compatible with many other trees. It might also have flowers that are very attractive to pollinating insects. Flowering crab apples are like this.

To answer your question about saving seeds: names are confusing! Open-pollinated seed (like for annual vegetables) keeps its name as long as it hasn't crossed with another variety. If you grow Noble Giant spinach by itself and save the seeds, that's still Noble Giant spinach. If it crosses with Bloomsdale Longstanding spinach, the plants that grow from those seeds are a hybrid, no longer Noble Giant. People sometimes name and sell hybrids like this (this is hybrid vegetable seed). Only the seeds that are the direct offspring of two open-pollinated varieties count as the named hybrid. If you save seeds from a hybrid, it loses its name and becomes a new, exciting breeding population.

Named varieties grown from cuttings are different. All plants with the same name are clones of one original plant. Take your Limelight oleaster, for example. If you saved seed from it (assuming this is even possible), the plants that grew would not be Limelight, regardless of whether or not it was self-pollinated. They would be interesting new plants with traits inherited from their parents.

As for your elaeagnus questions: I'm not sure! My guess is that the elaeagnus x ebbingei will pollinate each other (and they appear to be partially self-fertile, so there should be SOME crop either way), but not the elaeagnus multiflora (also partially self-fertile). Cross-species pollination is usually tricky. If it DID work, and you got viable seeds, the offspring would be a horticultural breakthrough!

Edit: Didn't realize until after posting how much I was just repeating what S Bengi said...sorry!

G Prentice wrote:Thanks - very useful!

If a crab apple pollinated a Granny Smith, for example, the fruit produced is just Granny Smith in characteristics, the fruit isn’t affected by the crab apple (smaller size) etc. - is that correct? But if I were to collect the seed from the Granny Smith apples and grow trees from them, the characteristics of the apples on the new trees would be a mix of the granny smith and the crab apple - the apples might be of a size in between a Granny Smith apple and a crab apple?

Yes and it would also be a mix of everything that was hiding in the genetics of both trees.  Since a granny smith is already a cross between a cultivated apple and a crab apple I would guess at the offspring of your hypothetical cross being closer to a crab apple than a domestic apple.

So, when you buy a fruit tree it’s probably from a cutting  than grown from seed (so that they can be sure what they’re selling you)?

Skandi Rogers wrote:

G Prentice wrote:Thanks - very useful!

If a crab apple pollinated a Granny Smith, for example, the fruit produced is just Granny Smith in characteristics, the fruit isn’t affected by the crab apple (smaller size) etc. - is that correct? But if I were to collect the seed from the Granny Smith apples and grow trees from them, the characteristics of the apples on the new trees would be a mix of the granny smith and the crab apple - the apples might be of a size in between a Granny Smith apple and a crab apple?

Yes and it would also be a mix of everything that was hiding in the genetics of both trees.  Since a granny smith is already a cross between a cultivated apple and a crab apple I would guess at the offspring of your hypothetical cross being closer to a crab apple than a domestic apple.

Yes when you buy a fruit tree, if it is a named cultivar it is a cutting (clone/graft), this is so that you know exactly what you are getting.

They sometimes sell seedlings for say native pawpaw (the fruits are up to 1lbs) so even the worse one is still going to be relatively big. And they don't ship well so people usually aren't too picky and they mostly bear true from seed(because they aren't a hybrid like most commercial apples which is usually a cross between crabapple and apple)

G Prentice wrote:
If a crab apple pollinated a Granny Smith, for example, the fruit produced is just Granny Smith in characteristics, the fruit isn’t affected by the crab apple (smaller size) etc. - is that correct? But if I were to collect the seed from the Granny Smith apples and grow trees from them, the characteristics of the apples on the new trees would be a mix of the granny smith and the crab apple - the apples might be of a size in between a Granny Smith apple and a crab apple?

That's correct. If you had a crab apple pollinate a Granny Smith, the apples would be normal Granny Smiths. You'd have to grow out the seeds to get hybrid characteristics. When people say that fruit is bigger/sweeter due to being pollinated, this is because plants can often tell how many viable seeds are inside a fruit and devote resources accordingly. If an apple is badly pollinated and only has one or two seeds, the fruit will probably be small and misshapen -- the apple tree doesn't want to put lots of effort into feeding just a couple of seeds. If it's pollinated very well, the resulting fruit is more likely to be large, sweet, and well-formed.

G Prentice wrote:
Elaeagnus x ebbingei is a hybrid species, right? I find it a bit confusing that hybrids are given new names that don’t tell you who the parent species are - I.e. ‘ebbingei’. I found one web page that said the parent species are ‘ a cross between E. macrophylla and E. pungens (or perhaps E. x reflexa)’, but otherwise it wasn’t easy to find info’ about this hybrid, which seems strange given how common it is.

Yeah, taxonomy is messy and weird. The "[example genus] x [name]" format always indicates an interspecies hybrid within [example genus]. It is a shame that the name gives no clue as to the parentage. Information can be hard to track down, even for common species.

E. macrophylla and E. pungens are both reported to have 28 chromosomes. I couldn't figure out how many chromosomes E. multiflora has. If it has 28, the odds of it being cross-fertile with E. x ebbingei are much higher. Now I wish I had the relevant plants so I could try the cross!

It looks like Elaeagnus x ebbingei's name is officially Elaeagnus x submacrophylla now, but both names are in use. Confusing.

Named cultivars grown or grafted from cuttings have their advantages (predictable, sometimes fruit earlier, can be a way to propagate a great sterile plant), but in my opinion, growing from seed is definitely worthwhile. If you like the parents, you'll probably get offspring that you like, too. You might get something better than the parents. If you get something you don't like, you can always use it as rootstock for grafting a better plant onto (or just chop it down). If it sounds fun, try it!

Thanks :) Plants are really quite amazing. Interesting that they moderate fruit size based on the number of viable seeds.

The baby goumi's and saskatoons have arrived (only 10-20cm tall! - couldn't find larger specimens from UK nurseries). Will have to grow them on in pots a bit first as they look very vulnerable to trampling at the moment.

J. Hunch wrote:

G Prentice wrote:
If a crab apple pollinated a Granny Smith, for example, the fruit produced is just Granny Smith in characteristics, the fruit isn’t affected by the crab apple (smaller size) etc. - is that correct? But if I were to collect the seed from the Granny Smith apples and grow trees from them, the characteristics of the apples on the new trees would be a mix of the granny smith and the crab apple - the apples might be of a size in between a Granny Smith apple and a crab apple?

That's correct. If you had a crab apple pollinate a Granny Smith, the apples would be normal Granny Smiths. You'd have to grow out the seeds to get hybrid characteristics. When people say that fruit is bigger/sweeter due to being pollinated, this is because plants can often tell how many viable seeds are inside a fruit and devote resources accordingly. If an apple is badly pollinated and only has one or two seeds, the fruit will probably be small and misshapen -- the apple tree doesn't want to put lots of effort into feeding just a couple of seeds. If it's pollinated very well, the resulting fruit is more likely to be large, sweet, and well-formed.

G Prentice wrote:
Elaeagnus x ebbingei is a hybrid species, right? I find it a bit confusing that hybrids are given new names that don’t tell you who the parent species are - I.e. ‘ebbingei’. I found one web page that said the parent species are ‘ a cross between E. macrophylla and E. pungens (or perhaps E. x reflexa)’, but otherwise it wasn’t easy to find info’ about this hybrid, which seems strange given how common it is.

Yeah, taxonomy is messy and weird. The "[example genus] x [name]" format always indicates an interspecies hybrid within [example genus]. It is a shame that the name gives no clue as to the parentage. Information can be hard to track down, even for common species.

E. macrophylla and E. pungens are both reported to have 28 chromosomes. I couldn't figure out how many chromosomes E. multiflora has. If it has 28, the odds of it being cross-fertile with E. x ebbingei are much higher. Now I wish I had the relevant plants so I could try the cross!

It looks like Elaeagnus x ebbingei's name is officially Elaeagnus x submacrophylla now, but both names are in use. Confusing.

Named cultivars grown or grafted from cuttings have their advantages (predictable, sometimes fruit earlier, can be a way to propagate a great sterile plant), but in my opinion, growing from seed is definitely worthwhile. If you like the parents, you'll probably get offspring that you like, too. You might get something better than the parents. If you get something you don't like, you can always use it as rootstock for grafting a better plant onto (or just chop it down). If it sounds fun, try it!

The responses from writers Benji and Hunch explained monoecious, dioecious, genetic compatibility (and incompatibility), etc. quite well and that this is all about mixing the gene pool by outcrossing. Most flowering plants produce flowers that contain both sexes, but some flowering plants (and some non-flowering plants - such as conifers) have flowers that are of only one sex, either female (pistillate) or male (staminate). This is where the terms "monoecious" and "dioecious" are used. A look at the roots of monoecious/dioecious might help with remembering the basic meaning of these two terms. The "-oecious" is derived from the Greek word "oikos" meaning, as one translation, "home". Also, "mono-" means "one", and "di-" means "two". So, put altogether, "monoecious" means "one home for both sexes of flower" = female and male flowers are found on one plant (squash plants have separate female and male flowers on the same plant), whereas "dioecious" means "two homes for the 2 sexes of flower" = female and male flowers are found on separate plants (persimmons, typically, have female flowers on one plant and male flowers on a separate plant (with some exceptions). Then, to mix it up even more, there are various other combinations.