Citrus > Cold Hardy Citrus
Long term cold hardy citrus breeding project
Walt:
Thank you all for your useful replies.
Ilya11, I agree that the precocious trait is recessive. But it is worth the wait since this a long term project.
I didn't know about Swamp lemon and Poncirrus+. Do you know where I can get them? I'll google as soon as I get done with this post. It sounds like they would be worth having even if I wasn't breeding. Any idea of the inheritance of the edible trait?
I agree that most of my work will be with deciduous stock. Even the deciduous trees mostly won't be hardy here. Evergreen trees are out of the question, except protected as breeding stock.
Farmche. I am quite interested in your Flying Dragon seedling. I am suprized at an edible fruit from that source. Cutting and/or seed would be very usefull
Isaac-11. I am looking for collaborators. I expect this to take 30 years if I am very lucky. Likely it will take longer. And I am 67 years old. So if I don't get collaborators, I am only amusing myself, not really doing useful work.
SoCal2warm. I'll be keeping a clone of each seedling to fruiting. I'll want to cross the most cold hardy with the best fruit in each population in each generation. My plan is to intercross the 10 best trees in each population in each generation.
As for your suggestion to backcross the F1 trees to P. trifoliata, that would be population 3 above. Actually, I plan to make a second backcross to P. trifoliata if necessary. That would be population 2.
So is anyone crossing Swamp Lemon, Poncirus+ or the Flying Dragon seedling with quality citrus or kumquats? If not, times being wasted.
Walt:
I read a paper written way back that said the Citrus x P. trifoliata F2 is less winter hardy than the F1., and that hardiness is less in each generration.
I think I know the explanation.
In the F1, all the genes for winter hardiness are there, but only one copy of each. We all knew that.
In the F2, 25% of those genes are there with 2 copies. Good. And 50% of the genes are there with single copies like the F1. No further loss there from the F1. But 25% of the genes for winter hardiness are not in a given F2 plant. And in the F3 25% of the genes hetrozygous in the F2 are gone, and so one.
It is not just that genes are being lost, the genes have co-evolved and some of the genes remaining won't work well without the genes that are gone.
If I just worked selecting in the F2, F3, F4, etc., selection won't be effective on those genes that require those genes that are missing. So selecting only in population 5 won't be effectively selecting for all genes involved in winter hardiness. Only as some of the genes that have some effect alone are selected will the others start becoming effective and be acted on by selection.
That is why I'll backcross the F1 to P. trifoliata, to have more of the hardiness genes present. This will allow selection to work on those genes that need other genes to interact with. A second backcross, Pop 2, may be needed to get the majority of genes available for selections. That remains to be seen
In the same way, flavor is the result of many genes interacting. Population 8 will at first only be able to use cold hardy genes that have significant effect without all those other genes which will be missing, But it will have all the genes necessary for good flavor, plus some genes for bad flavor which will be discarded.
Walt:
Farmche. You mentioned early fruiting mandarins. I haven't looked into them. I should.
So far, I have been collecting and growing only pre-existing poncirus hybrids so I could get on with the breeding. I plan to aquire Clementine this spring as it makes sexual seeds. I realize that a problem I'm not addressing yet is the short season here.
Ilya11:
Walt,
Both Swamp Lemon and Poncirus+ were described on defunct CitrusGrowers forum.
Below is an extract of this discussion presented by Sylvain on the AgrumesPassion French forum
http://www.agrumes-passion.com/poncirus-citranges-porte-greffes-rustiques-f67/topic5861.html
Poncirus+ have essentially no internal sticky oils and it seems that its seeds contain a single embryo.
On the left is juice of the regular poncirus, on the right that of Poncirus+
Next spring I am planning to cross them in a hope of obtaining even better quality of fruits.
I shall be glad to provide you hybrid seeds, if you are interested.
I am not fully agree with your reasoning for rejection of of the progeny of direct hybrids between poncirus and edible citrus.
Of course, if you consider all the plants in F2, F3 and so on generations, they become more and more heterogeneous in respect of the presence of genes for hardiness, but due to the chromosome crossing-overs the two genomes will be progressively present in the smaller and smaller intermingled fragments finally resulting in the separation of genes for bad the quality of poncirus fruits from the genes of hardiness in particular plants. This will be less possible in your pop3 and pop2 populations.
If you select for extreme hardiness ( comparable to that of poncirus ) in each subsequent generation of intercrossing inside pop5 population, and simultaneously keep selection for better and better hardiness, discarding the rest, you will produce hardy plants with higher and higher proportion of edible citrus genome.
SoCal2warm:
Walt, I'll collaborate with you.
It's true I have no interest in something that is mostly trifoliate in its ancestry, but maybe I can use what you develop to hybridize something and you can take what I develop and cross that with trifoliate.
If I can make a suggestion, you should consider using an indoor grow tent to accelerate growth. I believe it's possible to go from seed to fruit in as little as 3 to 4 years if the temperature is constantly kept above 75 degrees and the humidity is contained (and the potting soil is kept consistently watered, makes sure the plant containers allow plenty of root space as well). You may be able to find a grow tent on the internet for under $45 (2.5 x 2.5 ft or 2 x 4 ft seem to be economical sizes). I usually use incandescent/halogen bulbs inside during the Winter, and have one tent with a little 250W heater on a thermostat temperature control outlet. (I put a gallon container of water right in front of where the heater blows to help keep the temperature moderated, and block the path of dry air to help avoid it causing any of the plants to get dried out)
I hope to breed something that is going to be supermarket quality in taste but survives without much trouble in a zone 8 climate (not just zone 8 but a cool zone 8 climate where the period of summer heat is not that long). This could be pretty useful to someone trying to breed cold hardier citrus because you would already having something that could survive a fair level of cold and tastes good, so it would be a shorter jump for you to get something with extreme cold tolerance that tastes acceptable.
Anyway, hope to stay in touch over the next few years.
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