Heterozygosity and zygotic breeding lines

[a_Vivaldi]

While I am nowhere near up to speed on all the literature, most of what I have read indicates that, at least for polyembryony, which associates closely with nucellar seed and is a major practical hindrance for breeding, is controlled by a single dominant gene, with a variety of genetic and non genetic factors affecting the degree of polyembryony. What I am wondering is if most polyembryonic varieties are heterozygous, carrying a copy of the recessive allele for monoembryony and thus zygotic seedlings, or if the years of selecting zygotic seedlings from large populations of nucellar seedlings bred from two polyembryonic parents has lead to many if not most polyembryonic citrus to being homozygous for that darned gene.

Some are easy enough to know, since we have many varieties that are F1 children of pomelos, citrons, etc. But for other varieties, say satsumas or the various citromelos with grapefruit parentage, do we know if they tend to be heterozygous?

The practical side to all of this comes down to how many generations are needed and if any back crossing to the zygotic parent is required to eliminate polyembryonism.

[Lauta_hibrid]

In the end I understood why you were talking about Herterozygotes 😅... it seems to me that it is something with which we do not have access or tools, we would have to have a laboratory to deduce what the monoembryonic seedling of a population would be.  We depend on luck and many generations that each one can take 7 years to see the results (fruits).  It is better to know which varieties are monoembryonic, or which have a high percentage of zygotic embryos (true offspring from fertilization with pollen).  I would like to add a few things:

1st in a scientific work it was seen that 2 seedlings can grow from a single seed but both are hybrids, it seems that some cell of the embryo is released and forms a second "identical twin brother").  I believe this is what I saw in my hybridization experiences with Nagami (zygotic monoembryonic) and limequat eutis (zygotic monoembryonic) which also gave me 2 seedlings in a proportion of 1 in 50 seeds. 

2nd there are times that off-type varieties appear, such as monoembryonic Poncirus and there is an orange that also came out with 60% zygotic embryos (I could not find details of the variety).  If you want, I will give you the information I collected from my experiences and works that analyzed this in scientific publications.

PS: there are also varieties that logically should be polyembryonic and are not, such as Tangor (Ortanique, kiyomi, clementina) that both mandarins and oranges are polyembryonic, however these came out monoembryonic.  or citranges like C 35 that has a high percentage of zygotic embryos, higher than orange and Poncirus.  My idea goes there, but if it is to provide a strategy you could mix oranges x kiyomi or clementine to achieve an "almost orange", impossible to distinguish as happens with ambersweet Orange (which is not an orange).

[Till]

I agree with Lauta_hibrid that purely zygotic varieties are the best starting point for anybody who wants a high percentage of zygotic seeds. The downside of such a choice is, however, that you have a very limited genetic pool for starting any breeding. It depends on the very special goals one has if that is a real downside.

As far as I know all oranges are mutations of a single ancient cross (Pumelo x Mandarine) x Mandarine. (I do not know what was father or mother.) On the one chromosome set oranges are pure mandarines, the second chromosome set consists of about 50% pumelo genes and about 50% mandarine genes. Oranges produce mostly nucellar seedlings. But there have been orange hybrids that are zygotic, namely: Sanford Citrange, Phelps Citrange, Clementine and Kijomi. There are also orange hybrids with a noteworthy percentage of zygotic seeds as C35. I conclude from that that all oranges are heterozygous for nucellar embryony. I would also assume that some citranges are only highly nucellar because of the Poncirus part of the cross.


Aside from these considerations, I would recommend to anybody who wants to make crossbreeding that he does not focus too much on the issue of nucellar embryony. I cannot boast to be a successfull breeder because most of my seedlings have not yet flowered. But I have produced a greater number of hybrids. So I can already tell from experience: Polyembryony and nucellar embryony are annoying but no real hindrance in many cases. If you believe that a certain plant has all the properties a good motherplant should have except zygotic seedlings then just try the cross. You may be surprised how many zygotic seeds you get! Or you may be disappointed. Then try it again with more flowers in more years. You will be likely to succeed. And when you succeed you will be faster as the one who waits the same time for getting a zygotic motherplant.

Today I harvested all my Yuzu fruits (very tasty by the way). Some had been pollinated by Dunstan Citrumelo. And surprise! About 1/4 of the seeds were green, the rest pale. That means that about 1/4 of all seeds must be hybrids and that an unknown number of the pale seeds must also be hybrids by the law of probability. (The green color comes from the citrus part of Dunstan Citrumelo, the pale color comes from Yuzu or the Poncirus part of Dunstan Citrumelo.) Ok, last year, I pollinated with Poncirus and had no hybrids at all, only nucellar seedlings. Does that matter? Only a year later my largely nucellar Yuzu gives my plenty of hybrids from a different but very interesting cross.
I got hybrids from 100% nucellar Calamondin, from 100% nucellar Tavares Limequat, from nucellar Vainiglia Sanguigno (very difficult though), from highly nucellar Dunstan Citrumelo, from Poncirus (nucellar seedlings unknown). Great, isn't it? But when I started my experiments I was so keen on getting zygotic mother plants. I was happy when I got Chandler. "Wow", I said to myself, "so many seeds in a fruit and all zygotic!" Yes, in theory. But I tell you something: Although my Chandler is full of flowers every year I got only one single fruit with seeds in it. All crosses were in vain except the one with "African Shadock x Poncirus". Poncirus pollen on Chandler - all in vain. Other pollen? All in vain. But Chandler pollen on allegedly nucellar Poncirus: one hybrid! I do not know what the problem with my Chandler is. Others were more successfull. But one thing I do know: There is a great difference between theory and practise. The good news is: Although the practise may laugh at your best theories, often it is more friendly to you than all earnest considerations.

[Lauta_hibrid]

I agree with Lauta_hibrid that purely zygotic varieties are the best starting point for anybody who wants a high percentage of zygotic seeds. The downside of such a choice is, however, that you have a very limited genetic pool for starting any breeding. It depends on the very special goals one has if that is a real downside.

As far as I know all oranges are mutations of a single ancient cross (Pumelo x Mandarine) x Mandarine. (I do not know what was father or mother.) On the one chromosome set oranges are pure mandarines, the second chromosome set consists of about 50% pumelo genes and about 50% mandarine genes. Oranges produce mostly nucellar seedlings. But there have been orange hybrids that are zygotic, namely: Sanford Citrange, Phelps Citrange, Clementine and Kijomi. There are also orange hybrids with a noteworthy percentage of zygotic seeds as C35. I conclude from that that all oranges are heterozygous for nucellar embryony. I would also assume that some citranges are only highly nucellar because of the Poncirus part of the cross.


Aside from these considerations, I would recommend to anybody who wants to make crossbreeding that he does not focus too much on the issue of nucellar embryony. I cannot boast to be a successfull breeder because most of my seedlings have not yet flowered. But I have produced a greater number of hybrids. So I can already tell from experience: Polyembryony and nucellar embryony are annoying but no real hindrance in many cases. If you believe that a certain plant has all the properties a good motherplant should have except zygotic seedlings then just try the cross. You may be surprised how many zygotic seeds you get! Or you may be disappointed. Then try it again with more flowers in more years. You will be likely to succeed. And when you succeed you will be faster as the one who waits the same time for getting a zygotic motherplant.

Today I harvested all my Yuzu fruits (very tasty by the way). Some had been pollinated by Dunstan Citrumelo. And surprise! About 1/4 of the seeds were green, the rest pale. That means that about 1/4 of all seeds must be hybrids and that an unknown number of the pale seeds must also be hybrids by the law of probability. (The green color comes from the citrus part of Dunstan Citrumelo, the pale color comes from Yuzu or the Poncirus part of Dunstan Citrumelo.) Ok, last year, I pollinated with Poncirus and had no hybrids at all, only nucellar seedlings. Does that matter? Only a year later my largely nucellar Yuzu gives my plenty of hybrids from a different but very interesting cross.
I got hybrids from 100% nucellar Calamondin, from 100% nucellar Tavares Limequat, from nucellar Vainiglia Sanguigno (very difficult though), from highly nucellar Dunstan Citrumelo, from Poncirus (nucellar seedlings unknown). Great, isn't it? But when I started my experiments I was so keen on getting zygotic mother plants. I was happy when I got Chandler. "Wow", I said to myself, "so many seeds in a fruit and all zygotic!" Yes, in theory. But I tell you something: Although my Chandler is full of flowers every year I got only one single fruit with seeds in it. All crosses were in vain except the one with "African Shadock x Poncirus". Poncirus pollen on Chandler - all in vain. Other pollen? All in vain. But Chandler pollen on allegedly nucellar Poncirus: one hybrid! I do not know what the problem with my Chandler is. Others were more successfull. But one thing I do know: There is a great difference between theory and practise. The good news is: Although the practise may laugh at your best theories, often it is more friendly to you than all earnest considerations.

That's good what you're saying, I would love to see those hybrids.  mainly Poncirus pollinating with Pummelo.  I have the hypothesis that Poncirus, when pollinated with citrus, can dominate the pollen part.  This is because of Morton and his great resemblance to the orange (his father).  also for talks with a genetic improvement researcher from Argentina.

[Till]

I should have time to make photos on Monday. The mother plants inherits so called plasma genes, genes not contained in the nucleus, and all cell organs. Do you know how that effects the hybrids? I have no guess how.


Maybe I shall add that Satsuma is also heterozygous for nucellar embryony. If not it could hardly be explained why Kijomi (Sweet orange x Satsuma) is zygotic.

Willow Leaf Mandarine is also heterozygous because its offspring Clementine is purely zygotic.

Grapefruits as Sweet Orange x Pumelo crosses should be heterozygous for nucellar embryony what would also explain why some citrumelos regularily produce some zygotic seeds.


My encouragement to use nucellar varieties as mother plant shall of cause not overstressed. There are varieties that are really difficult mother plants. Perhaps Morton citrange is such a candidate. And the pollen donor plays a greater role in the formation of zygotic seeds. So I do believe that certain crosses are close to impossible. I only wanted to say that nucellar embryony is not necessarily a great hindrance. And before you loose your time in search for zygotic mother plants as I first did it is probably better to just try what you have at hand even if nucellar.

[Ilya11]

Till, I do not see a reason why green embryos in your YuzuXDunstan come from Dunstan.
Both its parents have white embryos, while Yuzu is supposed to be an ancient hybrid of some kind of ichangensis (white embryos)  and mandarine (green embryos).
In self pollinated  Yuzu I have occasionally seen the seeds with salad color.

[Till]

Hmm. Then it can also be that the green embryos are from Yuzu selfpollination? Sounds plausible.
By "both parents" you mean the parents of Dunstan or the parents of the seeds, i. a. Dunstan and Yuzu?

All seeds of Yuzu pollinated with Staraji were pale.

Ok, I shall wait for the seeds to germinate and keep you updated.

At any rate my Yuzu seems to produce a greater number of zygotic seedlings so probably also hybrids.

[Lauta_hibrid]

Hi @Till!  How's that for your Yuzu?  Have you already used it to hybridize?  Does anyone know the percentages of Zygotic Yuzu seeds?  This year I will see if I can achieve any crosses but I have fruit using other species as recipient: Encore x Yuzu, Nova x Yuzu, Dekopon x Yuzu, Paraná grapefruit and flame x Yuzu, and lemon x Yuzu

[Till]

Hi Lauta_hibrid,
I have one cross Yuzu x Poncirus. There might have been more but most seeds got rotten. And I have pollinated Tavares Limequat with Yuzu. I got two hybrids. All hybridization attempts of 2022 were in vain. I had tried to pollinate Yuzu with Poncirus again.

What concerns the different seed colors I have written about I must perhaps revoke my very optimistic conclusions. I had to store the seeds in water for two days before I could sow them. At the time when I sowed them the color differences were almost gone. It can be that my optimism was overhasty. I am going to post a picture of the seedlings so that all can see how many hybrids realy were among the seeds.

Yuzu seems to have variants. The number of zygotic seedlings is not always the same. There also seem to be greater taste differences. Most Europeans like Yuzu, those in the state usually dislike it according to this forum.

Pictures of hybrids follow soon. I have to bring the children to bed first 

[Till]

Ok, here some photos. Many plants on the photos are yellow. The reason is our cold temperatures.

First, seedlings of Dunstan Citrumelo. Pollen was from C. ichangensis but I am not sure if the hybrids are from selfing or from the pollen applied. I see at least four zygotic ones:



Here older seedlings of Dunstan Citrumelo (pollen of C. ichangensis). Two hybrids with C. ichangensis, one big and one small. The seedlings with regulary trifoliate leaves are probably nucellar (= Dunstan Citrumelo as we know it):





Yuzu x Poncirus. Almost totally monofoliate, sometimes trifoliate leaves:



Calamondin x Poncirus, the oldest hybrid. Leaves trifoliate and very variable.



Calamondin x precocious Poncirus, besides a nucellar seedling:




Other Calamondin x Poncirus crosses. (I had more but not all had healthy roots.)



Poncirus x Chandler. I see at least one hybrid (the bigger one), possibly two (close to the middle). The rest are just Poncirus seedlings (nucellar? zygotic?).



Poncirus x Sucrena (the left seedling).



Poncirus x Sanford Curafora (look at the narrow leaves). Perhaps the other one is also a hybrid.




Other pictures are following...

[Till]

Some citrumelo seedlings. (Sacaton? Nursery confused names). From open pollination.



Poncirus x Batumi Citrumelo. There are hybrids among them but hard to recognize.






C. ichangensis x Amoa 8 (="Rubino" from Agrumi Lenzi). I would say one hybrid, the "big" one in the foreground.




Other pictures will follow...

[Till]

Vainiglia Sanguigno x Poncirus. It had root problems so has not grown very big. Its sibling (not on the picture) had to be saved by grafting.



Chandler x (African Shadock x Poncirus).



C. ichangensis x Chandler. Some are hybrids,others probably not.



Limequat Tavares x Yuzu. Two very similar hybrids (the bigger ones). There are also smaller nucellar seedings in the pot.



Perhaps the only zygotic seedling of Tavares Limequat that I did not intend. Grafted on Swingle 5 Star. Its own roots were very problematic. The trifoliate is Morton. I also had trifoliate hybrids but they died. (Beginner's mistakes.)



Changsha x Dunstan Citrumelo. Look at the trifoliate ones. The rest will be nucellar.



Poncirus x Amoa 8? I am not sure if there is a hybrid.



Kucle x Poncirus






Changsha x Poncirus (a Poncirus with many zygotic seeds).



Red Fingerlime x C. ichangensis. Do you see hybrids? I am not sure.




I have many more seedlings, mainly with Poncirus as mother plant. But the seedings are two small that I clearly see were the hybrids are. This is especially difficult because I made backcrosses of Poncirus F1 hybrids onto Poncirus.


I did not state here which Poncirus I have used in the various crosses. In the case of Kucle x Poncirus I used dried pollen from precocious Poncirus mixed with pollen of a Poncirus from my garden that has not yet fruited. I only know that it is pretty hardy and that its motherplant had fruits that my parents call quite good. When I did not state the Poncirus clone then it was a better tasting one.

[Nemanja]

It is an amazing effort, but I am not too hopeful about palatability. Do you have a Taiwanica? I think it would be a promising candidate for crossing as demonstrated by Virginia Fruit Grower's Lemandarin.

[Lauta_hibrid]

Vainiglia Sanguigno x Poncirus. It had root problems so has not grown very big. Its sibling (not on the picture) had to be saved by grafting.



Chandler x (African Shadock x Poncirus).



C. ichangensis x Chandler. Some are hybrids,others probably not.



Limequat Tavares x Yuzu. Two very similar hybrids (the bigger ones). There are also smaller nucellar seedings in the pot.



Perhaps the only zygotic seedling of Tavares Limequat that I did not intend. Grafted on Swingle 5 Star. Its own roots were very problematic. The trifoliate is Morton. I also had trifoliate hybrids but they died. (Beginner's mistakes.)



Changsha x Dunstan Citrumelo. Look at the trifoliate ones. The rest will be nucellar.



Poncirus x Amoa 8? I am not sure if there is a hybrid.



Kucle x Poncirus






Changsha x Poncirus (a Poncirus with many zygotic seeds).



Red Fingerlime x C. ichangensis. Do you see hybrids? I am not sure.




I have many more seedlings, mainly with Poncirus as mother plant. But the seedings are two small that I clearly see were the hybrids are. This is especially difficult because I made backcrosses of Poncirus F1 hybrids onto Poncirus.


I did not state here which Poncirus I have used in the various crosses. In the case of Kucle x Poncirus I used dried pollen from precocious Poncirus mixed with pollen of a Poncirus from my garden that has not yet fruited. I only know that it is pretty hardy and that its motherplant had fruits that my parents call quite good. When I did not state the Poncirus clone then it was a better tasting one.

I see great enthusiasm, I also have about 40 combinations of citrus and I have already started with the cold resistance project, I will see this year if I can find some to send seeds to the US for a friend.  He recommended that you name the photos by editing them with your cell phone, since it is very confusing to know which intersection is which photo.  What I don't know is why you don't know if it is open-pollinated or hybrid, since if you castrate the flower before it releases the pollen, you will know for sure that the cross has been made.  I am quite methodical and with aluminum strips from beer cans and a pen without ink I make raised writing to label the plants, since it will take years to bear fruit, that helps them not to get lost and to discard what has not been crossed.  Two questions: calamondin x Poncirus did you use calamondin as a pollen receptor?  If so, how many seeds did you have to spend to achieve the crossing, since out of 50 seeds I did not achieve a single crossing.  and 2nd you said that Yuzu x Poncirus does not give you trifoliate leaves?  Because all Poncirus hybrids have it as a dominant trait, it is the way to recognize a hybrid or a nuclear plant.

[Till]

I consequently wrote the mother plant first (as is convenient in biology).

I do not castrate the flowers because I pollinate too much flowers. I have not the time to castrate them. It is then a bit more difficult to recognize the hybrids. But I am quite optimistic that I can do it nonetheless. Trifoliate leaves are only one characteristic of Poncirus hybrids. There are many others (paired first leaves or not, form of leaves, taste, leaf texture, leaf size etc.). I think it will become quite clear in the second year which are hybrids. Many can be recognized already now when you have a close look at the plant. The same is true I think for most other non trifoliate hybrids.

Regarding the Yuzu x Poncirus hybrid it was clear from the beginning that it is not nucellar. And some trifoliate leaves were then I clear sign that it is a Poncirus hybrid. It is indeed startling that it is mostly monofoliate. I also had a Kucle x Poncirus cross that was almost totally monofoliate. My supposition is that Papada genes can supress trifoliate leaves. Another example would be N1triVoss (Ichang Papeda x Poncirus) on the origin of which, however, some have cast doubt. The other explanation (or lets better say guess) of monofoliate Poncirus hybrids is that they are triploid. Now, my Yuzu x Poncirus does not look like a triploid I would say.

Regarding taste: Well, the taste may in many cases be far from our dreams. Yet I am optimistic. Dunstan Citrumelo has a very good taste. The other Citrumelo I used is not a culinary revelation but has high potential for it is very aromatic and even a bit sweet. Batumi Citrumelo is also tasty, as is Sanford Curafora. The Poncirus types I used are also better tasting ones that are in some year so good that you can almost eat them out of hand. So I am optimistic that at least some hybrids will taste better than Morton. Yuzu x Poncirus has no Poncirus taste in its leaves. That makes me also optimistic. The sole goal of all Chandler hybrids and of the one Sucrena hybrid is to get hardy plants with low acidity. My goal here is not to get tasty hybrids. I just want to take one step into the direction of hardy and sweet hybrids. Vainigla Sanguigno x Poncirus was also an attempt to create a hardy plant with low acidity. In that case my goal cannot be reached as I now know. Low acidity in Vainiglia Sanguigno is recessively inherited (defect NOEMI gene). In the case of Chandler (Siamese Sweet in background) I can reasoably expect that 50% of the crosses have only about 50% of the acidity of the sourest parent. My knowledge about Sucrena is more limited but I have hope. Sucrena is sweet because it converts acids into suggars more early and faster than normal sweet fruits.

I had a Calamondin bush of over two meters with plenty of fruits. My pollination of it was exceptionally loosy. While I normally take care that I am earlier than the bees I only pollinated from time to time my Calamondin bush without caring how old the flowers were. Under this circumstances I got about five hybrids per year. So I think you with your careful method should have a pretty good rate of hybrids - at least with Poncirus. I only got one single off-type seedling from Calamondin that had no Poncirus in its background. This is telling since Chandler and Limequat often bloom at the same time. The one off-type seedling has darker green leaves and grows faster than Calamondin. Leaf form and size is very close to pure Calamondin.

I do not have Taiwanica. I often wanted to get it but was never very keen on it. I think I already have better tasting trifoliate hybrids with more hardiness potential. Don't you think?

[Nemanja]

In any case, this is indeed a very impressive undertaking. In your experience, how long does it take your seedlings to bear fruit? Do you subject them to cold stress or plant them outside as a selection pressure?

[Till]

I fear I need a lot of patience. I live about 500m above sea level. So even Poncirus does not grow well if planted outside. So I have to plant as many plants as possible under glas. There Poncirus needs about 7 years from seed to flower. Kucle x Poncirus was a bit faster but only two seedlings have bloomed so far - and did not set fruit.
I am going to graft many seedlings onto older plants in hope that they need only 4 years then.

Some seedlings will be planted outside but only those that can reasonably be expected to be hardy down to -20°C / -4°F. I will not test those seedlings that are most likely only as hardy as citranges. I need not know whether they can withstand -10°C / 14°F or -15°C / 5°F. It is not enough at any rate. I shall use these seedlings for further crosses as fast as possible. What I will test are the further crosses.

What I will plant outside are those many seedlings that do not contain very special genes, those in which only the overall gene combination may be of value. So all zygotic seedlings of my citrumelo that were produced by selfing will be planted outside. Also combinations like Poncirus x citrange. When they are not hardy enough to survive then they have no value for me at all. Even if they taste well they will not be better than existing hybrids except they are hardier.

But I shall not test for instance Ichang Papeda x Amoa8 or Poncirus x Sucrena. The latter ones are definitely not hardy enough but have value for me because they may contain the genes for bloody fruits or sweetness. When they are not hardier than existing hybrids they are still more valuable for me because they contain special genes.

So that is the logic of my testing. I will, however, make cuttings form some potentially hardy plants and test the cuttings out of curiosity. I shall do that as I have time. So I will probably not consequently do that.

[Ilya11]

Till,
There is a paper on quantitative trait hardiness where they used PoncirusXpomelo population with some seedlings able to withstand -15C. So it is worth to test outside PTXSucrena

[Till]

Ilya, I am thinking about it. I may test a cutting.

The climate here is special. In my childhood -20°C was very common, even for two weeks. Now, the lowest temperatures are about -10°C. Winters are cool and wet but usually not very frosty. Yet the growing season is still short (begin of April to end or mid of September) and late frost remains a problem. -10°C in April is well possible. That is a real challenge for Poncirus or citranges that have started to grow then. Yuzu does better in late frost. But its overall hardiness is not sufficient.

Only 30km away is one of the mildest areas of Germany (around Cologne and Bonn). Poncirus grows very well there and citrumelos did well for at least many years. The lowlands...