Triploid hybrids arising from crossing a diploid female (most alll common orange types) x tetraploid male most generally always provides a tree with good vigor, and also displays fruit with similarities of the male parent that provided the diploid gametes. For example, it appears that the red pigmentation of blood oranges when used as the male parent (pollen) is highly heritable. You can make various citrus varieties of your own, with colored pulp. - Millet

Interesting concept, but a few caveats:

1. Unless your female parent is monoembryonic, most seedlings will be clones of their mother, regardless of pollen. And if you're crossing orange by orange, there's no easy way to tell which are hybrids, unless you happen to get a really vigorous "bull" or a really dwarfed "runt."

2. Are there actually tetraploid blood orange varieties out there? Most of the blood oranges, like most other oranges of all types, are simple diploids. I don't claim to be an expert on blood oranges, but I don't know of a 4N one.

3. If you did successfully make such a cross, you'd need a high degree of parthenocarpy in the seedling, or it would simply fail to set fruit. Most oranges require at least one seed for a fruit to set. Triploid citrus tends to be exceedingly seedless (less than one seed per thousand fruit, in the case of 'Tahiti' lime). I suppose one might spray with GA as a substitute; otherwise, it may be a fruitless tree.

4. Remember that among the true sweet oranges, we're talking an average 10 years to first fruiting, under ideal, outdoor growing conditions.

Below is an applied viewpoint, not a theoretical one. Applied side may have the terminology askew to people that prefer to be overly technical.

The conundrum is that not all Citrus genetics studies were conducted using sexual means to generate a proposed hybrid, even when the resultant offspring was touted as being a hybrid by University and Experimental Field Station trials. There are times when asexual propagation did more total good to yield a so-called hybrid than sexual reproduction did.

Remember how plants to serve as germplasm came into the US. Most of the time whole plants did not come in but seed from fruit, fruit themselves and wood were shipped in instead. When wood was shipped in they were almost immediately budded onto a foreign rootstock which muddied up the genotype of the individual, meaning it was no longer pure. Take an impure individual and use it for sexual reproduction onto another impure individual and we can get offspring that do not all look alike. Select one out that is different than the others and most people would later feel it was a hybrid, when it may only be a selected variant form of one of the parent plants instead (even still a worthwhile plant). In other words we assume it is a hybrid, even though it may not be a bona fide hybrid genetically.

Triploid crosses through sexual methods usually developed a seedless progeny. Also, there were individuals from those crosses that were male-sterile as well. One nucellar line of Orange came about from a proposed triploid cross but it in itself was sterile, never produced a seed but wood taken from that plant and then budded onto a rootstock, even the same parent line rootstock originating from rooted cuttings, could yield fruit that could produce a seed. Take the seed from that fruit and grow them on and then we may have a plant that might be exciting to work with.

"For example, it appears that the red pigmentation of blood oranges when used as the male parent (pollen) is highly heritable. You can make various citrus varieties of your own, with colored pulp."

Pigmentation could be a color dominant trait yet be a recessive form trait (form is dominant to color in Oranges), So, it may require both the male parent line plant and the female parent to have the pigmentation factor somewhere in their genomes. I'd now rather work on introducing pigmentation into a new parent line plant using asexual propagation rather than going through the trails using sexual reproduction methods in Citrus. Why? I can get some results to work with a lot quicker.

Jim

Jim,
Are you saying that you can say graft a regular lemon onto a blood orange rootstock or interstock and get a pigmented lemon?

"Are you saying that you can say graft a regular lemon onto a blood orange rootstock or interstock and get a pigmented lemon?"

You can start out that way but you probably also have a ways to go to see pigmentation that will hold in short order and over time in the Lemon. In other words one initial prototype wood cross generally is not enough to see the introduced color hold in the Lemon. You are most likely going to have to use wood from the first put together plant and bud or graft it back onto the Blood Orange again. Once you have seedlings grown on that yield fruit that have the pigmentation in them then you can work solely on keeping this introduced trait in the Lemon with no more Blood Orange "outcrosses".

The hard part is determining which Blood Orange to use and if it were me to do all over again I'd probably experiment with several Blood Oranges unless we know the answer to this question. Which Blood Orange is stable enough in its genetics to pass along the pigmentation more readily in its offspring than others will or have? Of course knowing this answer saves us a lot of time if we were to choose to breed these plants by sexual reproduction means instead. Then, which Blood Orange or Blood Oranges is or can be compatible to host a Lemon scion and can live long enough for us to be a viable rootstock for us?

Either way we will have to grow seedlings on but we also can advance how soon we will see fruit set on the tree in the process. I've seen 1 1/2" - 3" caliper flowering age wood used as scions for two to five year old Dogwood rootstock. I've seen the same in Deciduous Magnolias using some of the flowering Yulans on two to three year old Sprengeri Diva rootstock as well to yield a put together plant that will bloom a whole lot sooner than if we chose to wait years to see the plants set buds otherwise. Yulans can take up to 20 years to bloom but grafted plants using this method may yield blooming plants in 3-5 years. Not bad at all when dealing with Campbellii and Mollicomata forms. Then we can take wood from those put together plants and graft them onto one year old seedling rootstock and lo and behold we can also see a flowering tree in about 5 years in some cases. A five year wait is nothing as compared to a 20 year wait to see the first bloom otherwise.

Here is your quandary: the amount of pigmentation in the Cara Cara Orange is not the same as the old plants had for richness of color of pink in the flesh. That Orange, for color retention purposes only, probably should not have been grafted or budded onto foreign rootstock. (but the frequency at which you may see a branch sport come about that yields fruit with richness of pigmentation color again can occur in that when grown on from seed and propagated onto the same parent line understock may hold quicker than going through all of the steps later on that will eventually lead to a Cara Cara that has the old pigmentation color back in it.)

Even the Red Lime was felt to have some Orange blood in its genome at one time but this was only surmised by some people, was not proven. Also, the red pigmentation in the flesh which can carry (bleed) into the albedo and from a mutation, the Lime was able to yield some red streaks in the flesh of the fruit that did hold when left alone, not budded or grafted onto another Lime or Lemon. What we want is for the red streaking to hold from plant to plant no matter which Lemon or Lime it is grafted or budded onto.

I would definitely want to bud or graft a Blood Orange onto a Lemon rootstock as a backup plan to introduce pigmentation into the Lemon. I'd prefer to use a Lemon rootstock for my work rather than have a Blood Orange as my understock but my preference would be to take wood from the Blood Orange x Lemon (note: in the old days the pollen parent was listed first but since this is not a true cross I am listing it here like this to eliminate confusion) and grow it on to be my rootstock and then use wood from the Lemon x Blood Orange to be the scion and go from there. I'd also want to use the reverse process of having the Lemon x Blood Orange be my rootstock and have the Blood Orange x Lemon be my scion just because and can either merge these woods later or work on developing two lines later using only Lemon as my rootstock for the, down the road, anticipated pigmented Lemon.

When we read of a Mandarin that came from a King x Dancy cross we also had a "Kincy" Mandarin that came from a Dancy x King cross as well. I'd prefer the Blood Orange and the Lemon parents to be the same cultivar in both instances. Even though getting what I want later on from asexual propagation will take a long while to get I still want two control plants (F1 from the initial wood crosses) from both lines to have on hand as I may want to backcross on both parents later on. One to reintroduce pigmentation if need be and the other to see if the pigmentation holds when plants are later on grown from seed to see if the pigmentation is present and can hold in the fruit. I realize that perpetual budding once we see some pigmentation in the fruit may save some real time and effort but I'd want to be more sure that the pigmentation will hold for a long time as opposed to seeing the pigmentation later become minimal or even become absent later on perhaps..

Mr.shep wrote in the UBC BGCPR Maple forum of a Japanese Maple called in the nursery but was not ever officially named 'Red Seiryu' which gives some insight into how long it can take to achieve a Maple that shows red color that was introduced into a green Maple using a red parent line rootstock plant to do it and have the progeny stay red even when grafted onto green seedlings. Even several years later a Maple pictured in that forum, not referred to or called 'Red Seiryu' either, still shows enough of the introduced red in the leaf coloration. Even after apparent years of grafting it onto green seedling rootstocks. The Maple was outlet to collectors roughly 25-30 years ago and seems to have held up pretty well, all things considered, while dealing with years of unknowns as to what others did or have done to and done with this Maple. It is still red is what matters to me!

Jim

I have never before seen any suggestion that a rootstock can modify the scion variety in any way that can then be propagated and inherited.
Is there any scientific evidence for your 'wood crosses'?

Snickles, I don't understand a word of what you're saying.
Nothing resemble in any way to what I learned and taught.
(Few tens of years before I used to teach plant genetics at an agronomic university institute in Central Africa).

Grafting to a rootstock does absolutely nothing to the genetics of the scion. and Cara Cara is a different red from the blood oranges because it is not a blood orange! It uses lycopene (as do tomatoes, watermelons, and grapefruit), while true blood oranges use anthocyanins (as do plums and raspberries). Grafting had utterly nothing to do with it.

Dr. Manners, thank you for your follow-up caveats to my initial post that started this thread. I have taken several days to think about the caveats that you have offered.

I'll make just a couple comments.

1. The "Fun Experiment" as I posted is word for word taken from the book "Citrus Genetics, Breeding & Biotechnology" by Igrar Ahmad Khan. I have only added the ( ) to help identify by using a more common word, such as when I wrote "(pollen)". Reading the text of this book, I would say the book is an extremely scholarly text.

2. Your caveats have a lot of truth, which I must acknowledge. I would only partially accept your caveat numbers 3 & 4, due to GA3 (which you mention, but the book does not) and do to the shorting of the maturity factorof citrus trees by greenhouse grown trees (which I grow).

I do appreciate you for your knowledge concerning citrus, which is vastly greater then mine, however, I must also accept the knowledge of Mr. Iqrar Ahmad Khan and the many hundreds of scientists that have supplied the references from which the text is based.

I offer this response only as a means of further discussion. Let me give an example of a change of a long held belief concerning monoembryonic citrus varieties. I know find out, by reading the above book, that "monoembryonic" does not necessarly mean "monoembryonic", but that "monoembryonic embroy varieties can also have many nucellar embryos via in vitro procedures. My feeling is that there is truth in the "Fun Experiment", even if not in as straight a method as this post projects. Lastly, I don't think it is all the difficult to determine which seedlings are hybrids, at least within a small acceptable and reasonable error percentage, at least in a non-lab analysis situation, such as a serious citrus hobbyist arena . Thank you for your consideration. - Millet

What about the question 2? Where and how can we get tetraploid citrus?

Millet, I certainly did not mean to imply that the fun experiment was without merit or that it should not be tried; rather, that those reading it who have little or no experience growing citrus should consider that there may be a reason this has not been done hundreds of times already, always with complete, quick, easy success.

I am interested in the tetraploid idea. I'm only aware of one tetraploid that is (sort of) readily available, and that's the 4N Key Lime (not the common one). Also Dr. Jude Grosser (U. Fla.) has made some artificial tetraploids by protoplast fusion. But I don't know of any of the common palatable varieties of citrus that are tetraploids. If there are some known, I'd be most interested in hearing about them. Certainly, the premise of the experiment is valid -- cross a 4N with a 2N and you normally get 3N offspring, which will likely show stronger traits of the 4N parent. But the big question is, where do you get the 4N parent? One could create 4N blood oranges with colchicine, but that would normally be done with embryos, so you'd have even another generation to get through juvenility. Perhaps mature tissue could be doubled in tissue culture, then regenerated as a physiologically mature plant. I don't know if anyone has done that?

Tetraploidization seems to occur "frequently" in Citrus polyembryonic genotypes. Work done at UCR Riverside found that 2.5 percent of nucellar progeny taken from a broad range of genotypes are tetraploid. About 4 percent of Poncirus are found to be terraploid. The citranges Troyer and Carrizo averaged 3 percent tetraploid. Although I am unable to verify the percentage of tetraploidization in Blood oranges I would assume the percentage would run about the same. Chromosome doubling of nucellar stock seems to be the general rule. - Millet

A comment concerning Snickles post, and the various responses received: A tree propagated from a cutting can be in someways advantageous to a variety that usually is propagated by grafting, since a tree from a cutting has ALL THE CHARACTERISTICS of the parent, but one started from a graft invariably ACQUIRES CERTAIN CHARACTERISTICS from the rootstock, and is therefore NOT ONE HUNDRED percent identical to the parent. (Granted this difference might be more pedantic than material) Perhaps, this situation might be in Jim's writings.. - Millet

There are some interactions between the grafted cultivar and the rootstocks, but the original DNA of the grafted cultivar is retained and is not changed. Practically, I agree with Millet, that the changes in the grafted plants are more phenotypic expressions rather genotypic. The interaction with rootstock is considered phenotypic, very much like the grafted cultivar's reaction to a different environment, in this case, the rootstock is part of that environment. While the reaction is mostly phenotypic, the grafting process is a stressful event and can sometimes, very infrequently, result in a sport mutation from the graft, where the resulting genetic make-up of the graft is slightly changed, and a new cultivar is discovered by the very observant person.

phenotypic - changes in expressions such as stature, fruit quality, size, cold hardiness without changes in the DNA or the genetic makeup. The cultivar's reactions to grafting on different rootstocks or planting in various climates are good examples of phenotypic expressions.

genotypic - changes in DNA, though are very often expressed phenotypically, it does not always show. Examples are hybridization such as the fun experiment mentioned by Millet, mono-embryonic seedling propagation (except for Yuzu and perhaps other rare types), irradiation experiments, chemically induced mutations, bud sport mutations, perhaps trans RNA modification (am not sure but must read deeper if it really changed the plants at cellular and genetic level) etc.

Joe, thanks for a very good and informative post. I only add that although the new grafted scion still retains its original DNA, it now becomes a "DNA Plus Tree". That is, it now has its original DNA PLUS all the acquired characteristics from the rootstock. Therefore it is not 100 percent the same as it parent. These characteristics almost always make for the better tree, then its parent. Jim might be correct in saying it is different from its parent tree. - Millet