Tropical Fruit Forum - International Tropical Fruit Growers

Citrus => Cold Hardy Citrus => Topic started by: SoCal2warm on August 16, 2019, 01:00:36 PM

Title: I've noticed that Poncirus hybrids are slower growing
Post by: SoCal2warm on August 16, 2019, 01:00:36 PM
I've noticed that Poncirus hybrid seedlings are slower growing than other seedlings.

I've been growing a large number of different seedlings, so I think I can make this observation.
I've grown 2 seedlings from US 852 (Changsha mandarin x trifoliate), 3 seedlings from Tai-tri (taiwanica x trifoliate), 2 seedlings from N1tri (ichangensis x trifoliate), and without exception they have all seemed to grow very slow, certainly relative to other seedlings.
I've also been growing numerous seedlings from Ichangquat (kumquat x ichangensis) and a few cuttings from C. ichangensis. The Ichangquat grows very vigorously, even more vigorously than Yuzu, which also grows vigorously. The C. ichangensis cuttings have grown relatively slow, but reliably, with steady, healthy, and continuous growth. I do also have one seedling from Thomasville citrangequat, it has grown about as fast as kumquat, only about medium vigor. Unfortunately I don't have any pure trifoliate seedlings to compare to.

I think this should not be surprising. When two different plant species are hybridized together that are farther apart from each other in terms of relation, the result is often offspring with a slower growth rate and slightly stunted, or often with generally poorer health. It's presumably due to slight incompatibility between the genetic makeup of the two parents, since they are so distantly related (This is termed outbreeding depression )

Obviously Poncirus trifoliata is less related to the general citrus family than other citrus species are.

For comparison, taiwanica is vigorous and fast growing, and Changsha mandarin is a little slower growing but its growth is very reliable and healthy.
C. ichangensis is also slower growing (slower than Changsha mandarin) yet with very healthy reliable steady growth.
The trifoliate hybrid seedlings are all even slower growing than C. ichangensis, and do not have as healthy reliable robust growth.

What's interesting here is that since I am growing seedlings of hybrids, we are possibly getting to examine the effects in the F2 generation.
I believe some of these seedlings may not be nucellar.
I know citrangequat is said to always have nucellar seed, but my seedling (I harvested it from the fruit myself) seems to have mostly normal unifoliate leaves, with only two malformed bifoliate leaves, reminiscent that it has some trifoliate parentage in its ancestry.
Around half the Ichangquat seedlings appear to have obviously variable leaf morphology, so are almost certainly zygotic.

I do also have a Dimicelli cutting (probably either a citrandarin, F2 citrandarin seedling, or maybe second generation citrandarin cross with the tangor 'Temple Orange' , its exact origins are a little ambiguous) and it has been growing rather slowly, though with steady reliable growth.

The only trifoliate hybrid I have grown with vigorous robust growth is Duncan citrumelo (trifoliate x grapefruit) but even it is not as fast growing as grapefruit (in warm growing conditions).

I know this is hardly a controlled scientific study, but I believe with the number of seedlings I have been growing, this is strongly anecdotal, and this generalized observation may have value.

Maybe someone here (I am sure there are plenty) who has grown Poncirus seedlings can comment on how they grow compared to other citrus seedlings.

If Poncirus hybrids tend to be much slower growing, it may be of particular importance to try to select the most vigorous seedlings in hybridization attempts. I believe there is a strong correlation between level of vigor and ability to recover after cold damage.
Title: Re: I've noticed that Poncirus hybrids are slower growing
Post by: kumin on August 16, 2019, 02:32:56 PM
I would separate cold hardiness from vigor. Vigor is displayed by rate of growth as well as duration of growth expressed by number of flushes and growth per flush. Cold hardiness consists of a number of factors: A. early initiation and retention of full dormancy, B. actual tissue resistance to freezing and freeze damage. I don't see vigor as being preventative of cold damage, and may be the opposite by exposing late, immature, succulent growth to freeze damage.

Recovery from freeze damage is a different matter, and vigor may indeed assist in repairing and overcoming winter damage. Therefore I would separate resistance to cold injury from subsequent spring recovery.

Vigor is desirable, but needs to by curtailed in the latter part of the season in order to allow the plants to achieve early and sustained dormancy in preparation for winter. A major difference between zone 6b Citrus and warmer areas is that achieving and maintaining dormancy is easier in the colder climates. The bottom line is whether the 6b plants can endure the cold under full dormancy.

An other factor is the plants ability, or lack thereof, to re-establish vigorous growth in the spring in cold wet soils after winter. Some plants appear to be stunted and slow in recovery.

In regards to Poncirus vs. it's hybrids, there are hybrid plants that are genetically more vigorous, as well as many that are stunted especially in the F2 generation. I find vigorous Poncirus hybrids to easily outpace pure Poncirus in growth. This may be a contributing factor in the greater hardiness of pure Poncirus.

Of the 69 survivors (with partial intact stem) out of 3,000 zygotic F2 citranges on trial, the tendency was for mid-range to dwarfish plants to predominate. None of the very most vigorous plants were survivors, these tended to continue growing too late in the season.

I am not a grower of pure Citrus species or cultivars and can't really comment on their vigor.

Title: Re: I've noticed that Poncirus hybrids are slower growing
Post by: Walt on August 16, 2019, 04:08:14 PM
I have grown seedlings from the following P. trifoliata.  35 from Stan Mckenzie for grafting, but not yet grafted (7 years), Laaz precocious I bought one year old seedling and 10 seeds), Flying Dragon (1 plant and some fruit for the seeds, which I've grown.), many, many fruit from Hong's Landscape In Wichita, Kansas.  He brought seeds from Korea decades ago, and two 3 m trees trees are still growing and my source of seeds now, and I have one tree from Oikos Tree Crops.
I'll disregard Flying Dragon, as it is somewhat slow growing for P. trifoliata.  These have all grown slower than my pure citrus, except the finger lime seedling from seeds I bought about 10 months ago.  Finger Limes have been the slowest growing of all citrus relatives I've grown. 
While P. trifoliata seems slow growing to me, I can't rule out that they would do better under other conditions.  They are almost all in the ground.  All others are in pots.
But I'll pay attention to growth rates.  But I'll be selecting for survival and flavor.

Kumin's post shows how many factors go into winter hardiness.  And I think there are even some more factors he didn't mention.
Title: Re: I've noticed that Poncirus hybrids are slower growing
Post by: SeaWalnut on August 16, 2019, 05:31:23 PM
Somme hybrids grow a lot faster than their parents.Most.famous example is the Paradox hybrid walnut and i also have a plum X apricot hybrid wich had grown giant and the trunk its almost 3 times thicker than the rootstock.
Title: Re: I've noticed that Poncirus hybrids are slower growing
Post by: Ilya11 on August 17, 2019, 04:02:41 AM
I do not think that such deep conclusion can be drawn by 7 seedlings mentioned by Socal2warm.
I have some extremely rapidly growing both F2 as well as F1 poncirus hybrids. One such seedling reached 2 meters high in two years and was not damaged by -9C freeze.
Title: Re: I've noticed that Poncirus hybrids are slower growing
Post by: Millet on August 17, 2019, 01:25:25 PM
Although we can gain some information from limited batch experiments, as Ilya11 writes above there is indeed a truer level of value in results gained from higher trial numbers.
Title: Re: I've noticed that Poncirus hybrids are slower growing
Post by: Bomand on August 18, 2019, 11:07:52 AM
I find that there will not be enough evidence in a small lot comparison to draw a viable conclusion as to growth rates. I plant several hundred of different rootstock seed and draw the general growth rates for that seed. I find that each one is dependant upon seed source, weather conditions, and care. So many factors effect growth rate that a general conclusion is all that one can glean from a particular group of plants.