Citrus > Cold Hardy Citrus

The Elusive Michigan Citrus: A Lifetime Experiment

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Lobotomy:
Hello, I live in North Michigan (5a-6b), and I'm trying to breed both Cold Hardy and True Citrus. I currently have multiple specimens of the 3 common Citrumelo varieties (Sacaton (clones), Dunstan (several nucellar and possibly zygotic seedlings), Swingle (clones)), Variegated Pink Lemon, and Moro Blood orange.

I'm also trying to acquire Poncirus+. I'd do anything for a live specimen, so hit me up if you know anyone who is selling clones! They're critical to my project!

I have a couple of crossbreeding projects I'd like to do. The first one, is crossing the Citrumelos back to Poncirus+, and then tasting leaflets from each seedling to check the Poncirin gene expression for P+ before I get any fruit. The intended result would be a larger fruit (although, not as large as a normal Citrumelo), and little or no Poncirin bitterness, and greater cold-hardiness, as the resulting hybrids would be 75% trifoliate. With hope and a little bit of luck, these hybrids should also grow in my fairly unique lakeshore microclimate. I have mild confidence that my Citrumelos could survive, as well, but it's right on the edge of what they are known to tolerate. If this succeeds, it should hopefully stand as a 'blank slate' Trifoliate hybrid that is cold hardy anywhere in the contiguous 48 U.S. States, with an edible, if possibly bland, or otherwise, feral flavor. At bare minimum, I'd like something worthy of note.

The second, is crossing both Poncirus+ and each Citrumelo to both Moro Blood Orange and Variegated Pink Lemon. The intended result is a 25% Trifoliate citrus with some cold and disease tolerance, but ultimately, edible fruit. I chose these varieties, because both of them should have traits that are visible as seedlings (reddish hue from the anthocyanin pathway in young growth, or variegation). I don't expect to put these in the ground, but I am going to see how well they tolerate the greenhouse when they're old enough.

If I succeed in one or both of my goals, the endgame is to cross the Poncirus+ x Citrumelo and resulting Lemon and Citrumelo hybrids, to have a hopefully improved 50% Trifoliate hybrid. The roadmap I've come up with for this should hopefully be the optimal route to introducing the genes I'm looking for. I believe introducing the allele(s) for the anthocyanin pathway will make an inherently hardier plant, as every plant I'm aware of with anthocyanin production seems to be, and I can't imagine that's coincidence.

I've also heard of a method for near-guaranteed sexual reproduction in plants, known as "Embryo Rescue". You basically take a fertilized, unripe, fruit, harvest its seeds, excise the embryo from the seed before Trifoliate's aggressive clonal DNA can turn the seed nucellar, then you culture it until it's ready to plant. I've only seen this done to corn, do you guys think it's possible to do it to citrus? If so, I may make an attempt, if I can get in cheap enough.

A few key points regarding the experiment:

- I am doing this over several locations in the region, as I want the plants I'm testing in-ground to be isolates. Some locations are in the microclimate, some are not.

- This microclimate I'm referring to is ideal for growing Wine Grapes, Apples, Hardy Kiwi, and Montmorency Cherry/other stonefruit. It's known as The Grand Traverse Region, and its unique geography and water system allow for things to grow here that would otherwise be impossible, due to the warmth of Lake Michigan being dappled by recursive peninsulas. I'd liken it to Florida, if it didn't get so cold. Very harsh, moist, and sunny summers, perfect for these plants.

- As far as I'm aware, this may be the harshest environment that may also be viable for Citrumelo. Humidity is high year-round, temperature in the microclimate gets to about -3F/-19C, but only at night, and for ~3 days of the year. I have a specimen for indooring, and one for babying outdoors when it turns 2 years old.

- Soil type seems to be ideal, as The State of Michigan is 150% beach, and also a proverbial fertile crescent. Predominantly sandy with good flow. I've mixed the soil from my back yard into generic potting soil for additional loam, and my plants seem to love it. I even planted one Dunstan in just a pot of backyard dirt, just to see how well it does, and it's comparable in size to the rest.

- From the papers I've been reading, Sacaton Citrumelo will make nearly 100% nucellar seedlings as the mother plant. Does this mean I can get a hybrid if I pair its pollen with a True Citrus mother instead? I'm mainly asking to double-check my understanding.

- Poncirus+ will be the only plant in this experiment that I will plant in-ground, in the beginning, unless I'm able to take clones.

- I'm happy to take suggestions on other trifoliates and true citrus plants I should grab for their genes. I'm mainly targeting edibility, but I'll take hardiness, too.

Below are my Citrumelo plants. Swingle on the right, Dunstan in the center, Sacaton on the left. Sacaton seems to be the happiest variety so far, and all have been through their first winter, entirely unassisted by heat, I just left them alone in the spare room, and shut off heat to that part of the house. It did get below freezing in that room, and I wanted to condition them, but wanted also to control how cold it got, directly, which is my reasoning behind doing so. This is their first time soaking up direct sun since late October:









Any thoughts? I'm in drafting phase right now for this project, so if you know better than me, please speak up. I refuse to die until I can eat good tasting citrus that was grown in Michigan dirt. Please poke holes in my proposal now, so I'm not making a 30-year mistake.

Mulberry0126:
Hi there! Awesome project and looking forward to seeing how it plays out. We need more breeders in climates like yours - mine is only challenging enough for 25-50% trifoliate hybrids to be tested, whereas anything 75% or pure Poncirus is basically guaranteed to survive here.
Sacaton in my experience is highly zygotic compared to other citrumelos which have been highly uniform. Sacaton seeds from Lyn Citrus were probably around 15-20% zygotic whereas Sacaton seeds coming from the fruit of Stan McKenzie's tree are more like 50-60% zygotic or more! It's clear that there are multiple Sacaton strains floating around already. Stan's tree is also useful for breeding because the grafts flower in their second year. 5star also seems fairly zygotic.
I grafted some Poncirus+ for sale this year but they've been slow to grow so they're not ready yet. I'll also have some 1-quart grafted 5star and I have one 1-gallon grafted Sacaton.
kumin's Conestoga selections like 010/026 should also withstand your climate and may be interesting to experiment with, but your climate will definitely require some brutal selection. You may also be interested in back-crossing Citrandarins with Poncirus since they are very hardy already. I have some F2 seedlings of US-852 that are highly trifoliate and some may very hardy but with smaller, lower-quality fruit, probably similar to HRS 899 O/Q. Even then, fruit of this quality may be an achievement for your area nonetheless. Even Poncirus+ will be enjoyable to cultivate on your own land. Wishing you luck!

bussone:

--- Quote from: Lobotomy on April 02, 2025, 12:50:27 AM ---Hello, I live in North Michigan (5a-6b), and I'm trying to breed both Cold Hardy and True Citrus. I currently have multiple specimens of the 3 common Citrumelo varieties (Sacaton (clones), Dunstan (several nucellar and possibly zygotic seedlings), Swingle (clones)), Variegated Pink Lemon, and Moro Blood orange.

--- End quote ---

Northern Lower Peninsula or Upper Peninsula?

Are you growing outdoors or indoors? Because in zone 5, you're pushing your luck with poncirus. I've heard of it surviving 5b, but that was down by Chelsea, which is 6a now. Your hope with hybrids probably lies along the Lake Michigan coast line and only a few miles inland from there, which is 6b. I know poncirus does okay there, because the one I gave my mother is still alive. There's also a small zone of 6b along the Lake Erie coastline, but hybrids may struggle there because the soil is basically 6" of topsoil above a clay tennis court. (The Lake Michigan shore is on a sand dune, so it drains really well)

The trick w/ the northern shorelines is that while it moderates summer lows and helps the trees not freeze to death, it also moderates the summer highs, and citrus likes more heat than that.

Ilya11:
I guess what you described is quite solid as a project. Good luck with it. 
People  have been trying trying to produce hardy edible varieties for zones  6 and higher but unfortunately we are not yet there.
I do not quite understand your zone 5 climate, but for my humble opinion only genotypes very close to pure poncirus trifoliata will resist it. Introducing valuable features by multiple backcrossing will take so many generations with a necessity of controlling so many aspects of hardiness, fruit size and quality that are polygenic in nature. 
Probably an easier way would be to apply mutagenesis for pure poncirus or to its F1 hybrids with the second hardiest  citrus- Ichang Papeda. I know at least one clone of it -IVIA358 that gives fruits that smell and taste quite good.

Mulberry0126:

--- Quote from: Ilya11 on April 02, 2025, 12:05:49 PM ---I guess what you described is quite solid as a project. Good luck with it. 
People  have been trying trying to produce hardy edible varieties for zones  6 and higher but unfortunately we are not yet there.
I do not quite understand your zone 5 climate, but for my humble opinion only genotypes very close to pure poncirus trifoliata will resist it. Introducing valuable features by multiple backcrossing will take so many generations with a necessity of controlling so many aspects of hardiness, fruit size and quality that are polygenic in nature. 
Probably an easier way would be to apply mutagenesis for pure poncirus or to its F1 hybrids with the second hardiest  citrus- Ichang Papeda. I know at least one clone of it -IVIA358 that gives fruits that smell and taste quite good.

--- End quote ---

"Probably an easier way would be to apply mutagenesis for pure poncirus or to its F1 hybrids with the second hardiest  citrus- Ichang Papeda."

This is a valuable and probably overlooked approach. We already know there is variation in fruit size, seed count (sometimes environmental factors), and resin content (Poncirus+ and Poncirus++). Selecting for mutants and/or stabilizing valuable traits could provide results quicker.
Perhaps introgression of Yuzu/Papeda or Kumquat genes into Poncirus could even cause meaningful differences in fruit quality without sacrificing as much hardiness. Pummelo introgression is of course correlated with fruit size. Though to do so without hurting cold hardiness significantly may take several generations.
Now that I think of it, Ichang Lemon might be a valuable parent for such a task. I have a very promising open pollinated seedling that is likely Ichang lemon x citrumelo or another 50% Poncirus hybrid. Crossing it again with pure Poncirus several times over would be interesting, although I would need help or property in a colder state to know the lower limit of their hardiness.

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