Citrus > Cold Hardy Citrus

Cross of coldhardy citrumelo and quite coldhardy pomelo

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--- Quote from: Ilya11 on May 01, 2017, 04:12:07 AM ---Do we know what happened to this interesting hybrid?
I has not be able to find any further information on it.
In  leaf freeze resistance tests it was shown to have a similiar or even better hardiness than US119.

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I think this is an interesting question, if it should be possible to cross a quite cold hardy pomelo like e.g.bloomsweet with an very coldhardy citrumelo/Citrange like 5*, Dunstan or  Morton, to get better and bigger fruit than Citrange/citrumelo and perhaps little less cold hardiness - did you meanwhile get an answer Ilya ? Anyone else or is someone already working at this subject ?
best regards Frank

I planted a Bloomsweet close to a Dunstan citrumelo with the very intention of possibly making this cross in the future.

It will still be a long time until they grow big enough to fruit though.

The Bloomsweet is moderately close up against the house, on a south-facing brick wall, in a warm sunny spot that I thought would be most optimal to plant something that was going to be kind of marginal in this climate (Olympia, WA, zone 8a). So far the Bloomsweet is managing to survive.

I'm guessing probably around 55 to 70 percent of the seeds in Dunstan citrumelo are nucellar, meaning the percent of seedlings that could turn out to be hybrids is smaller.
The percent of nucellar seed could even turn out to be something more like 85 percent.

I just quickly looked up one reference that says the percent of zygotic seeds in Swingle citrumelo ranged from 9.3 to 17.7.
It could be higher for Dunstan citrumelo, but I believe Dunstan and Swingle originated as siblings, if I'm remembering correctly.

No idea what it is for Bloomsweet. The original parents of Bloomsweet are believed to be Kunenbo (which would likely be similar to Satsuma, at 90 percent nucellar) and pomelo, which are fully zygotic seedlings.

A variety with a very high percentage of nucellar seeds means it will be more difficult to use it as the female parent in making hybrid crosses, since most of the seeds will turn out to be genetic clones of the fruit parent, and you can't immediately tell which offspring seedlings are actual hybrids. In the absence of some identifying trait, at least. One common identifying trait that has often been used is if the offspring from a parent with normal leaves displays trifoliate leaf shape. Then they immediately discard all the seedlings with normal leaves, even though a portion of them could turn out to be hybrids as well.

I believe a Bloomsweet x Dunstan citrumelo cross could turn out to be very promising. A Dunstan citrumelo is not that far away from being edible (from what I've read), and I believe just one more cross is all it would take. The Bloomsweet is also supposed to be just a little bit insipid and could probably benefit from the stronger level of flavor from the Dunstan citrumelo.
Then, after making the first cross, I would grow a bunch of seeds from the hybrid and see if any turned out to have improved fruit quality from the first generation hybrid. Sometimes genes can get mixed around again, recessive genes can express themselves and certain dominant genes can get eliminated. (referring to sexual recombination from self-pollination)
That's what I would do.

The downside is, in these northerly climates which we are in, the time between a small plant and getting it to finally fruit can be very long.

I also want to say I'm very skeptical of a first generation Bloomsweet x citrumelo hybrid being able to survive in Germany zone 7. Bloomsweet is moderately hardy, but nowhere near zone 7 hardy. For that, I think you would have to grow several hybrids, and then from the fruits of each of those hybrids, grow many seedlings, and then you might finally see citrumelo-like cold hardiness again. Obviously more difficult than just simply creating a hybrid.

For the colder part of zone 8, and the very edge between zones 7 and 8, I think this would be a good idea.

thanks for your interesting post SoCal, you try already, what I thought could be done, but yes it is also in this combination still a long way. I whish you very good success.
For me also if I couldn' t perhaps plant such a cross without protection in ground in z7, it also could be charming, to leave the plant for example 50 weeks a year on the veranda of the house with small protection ind if there is 1 or 2 week cold spell, bring it only for this time in the greenhouse or garage.
How big/old are your bloomsweet and Dunstan ?

Keep in mind that Ilya had grown a Bloomsweet, he lives not that far away from Paris, in France, zone 8a, and it finally did not survive after a colder than normal winter.

My Bloomsweet, in the US Pacific Northwest, zone 8a, did survive a definitely unusually colder than normal winter, but it was covered by a special plastic sheet enclosure (although did having venting fabric mesh at the top), had two gallon water containers inside near the base to help prevent freezing, was probably additionally insulated by unusually higher than normal snowfall that winter, and even then the base of the trunk ended up suffering some significant bark damage and I wasn't entirely sure at the time whether the tree would be able to make it. And remember it is planted in a very optimal location near the brick wall of the house, on the south-facing side. (exactly 73cm away from the wall, I just measured)
This last winter the tree was able to survive through the winter with no protection, except that I did put a gallon water bottle up against it and covered it with a paper grocery bag on the one coldest night that winter.

--- Quote from: tedburn on December 28, 2020, 04:44:32 PM ---How big/old are your bloomsweet and Dunstan ?

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The Bloomsweet is only 1 foot 8 inches (51cm) high, and the Dunstan citrumelo is only about 2 feet 4 inches (72cm) high.
They are growing, but the length of the growing season here is not very long. They do grow great from about July to August.

My impression is that it is even more important to produce a large quantity of hybrid seedlings than the parent combination.
Regardless of which combination one choose, it might be a good strategy to backcross hybrids. e.g. a hybrid with good fruit quality but low frost tolerance with the hardy parent and a hardy but non-edible hybrid with the citrus parent. But one must always produce a lot of seedlings and select the best ones. Anything else would be a stroke of luck.
From the point of view of backcrossing, citrumelos would be best crossed with pomelos.

Everything else will work too, but if one want to cross in a certain trait, backcrossing is a way to plan.
However, onecan also just get lucky and find the desired traits in a random cross.
a contra is that pumelos take a very long time until maturity... so backcrossing is very long term strategy. So random crosses and large numbers of seedlings might be a better option in this case... when you consider your time...
But in any case, the chances increase the more seedlings are produced.

long talk short sense Bloomsweet x Citrumelo sounds good.


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