Poncirus polyandra turning yellow

[mikkel]

A Poncirus polyandra on trifoliata is turning yellow and seems to want to shed its leaves. I'm still not quite sure why this is happening. Normally it is evergreen

[bussone]

Is this different than what it has done in the past?

[mikkel]

It is a new graft on trifoliata. There is another graft that also turns yellow. Others are green as usual

[Lauta_hibrid]

Where did you get this species? Can you get seeds? I would love to add it to my collection. Have you tried the fruit?

[mikkel]

The origin must remain a secret but there are now several collectors who have them and a botanical garden in Germany also got them this way.
So far all the flowers are sterile and no fruit has formed

[christianmom]

mikkel, that yellow looks like an incompatible graft problem. I'm new to citrus, but I wouldn't rule it out. Incompatible grafts can also happen from all kinds of viruses that don't affect the scion or the rootstock on their own, but when you graft the two plants it can kill both.

[mikkel]

That could be the case, of course. But I've already thought about that, because it's autumn and many citrus hybrids nearby are changing colour. But since it's polyandra, there's really no reason for the colouring...
I'll keep an eye on it, it's only 2 graftings out of many...
It is grafted onto Poncirus trifoliata, like my other Polyandra grafts

[bussone]

That could be the case, of course. But I've already thought about that, because it's autumn and many citrus hybrids nearby are changing colour. But since it's polyandra, there's really no reason for the colouring...
I'll keep an eye on it, it's only 2 graftings out of many...
It is grafted onto Poncirus trifoliata, like my other Polyandra grafts

Is polyandra similar enough to trifoliata that it is responding to the rootstock going dormant in a manner that mainline citrus wouldn't necessarily do? (Poncirus has a lot of hardiness genetics that citrus does not, and it's not entirely clear whether or not polyandra also has them)

In short, polyandra on trifoliata may not respond like own-root polyandra would, and I'm not sure how studied this is.

[mikkel]

I can only compare with my other graftings and they are all evergreen. Even on trifoliata. That's why I find it exciting what the reason could be.

[mikkel]

Both plants have now shed most of their leaves. However, the branches seem to remain green and vital, seemingly healthy. At the moment I think it is unlikely that it is a graft incompatibility or an infection.
Nevertheless, it remains strange.

[Ilya11]

Could it be due to the influence of trifoliata roots?
Have you asked Sylvain if he has the same feature?

[mikkel]

that is also my guess, on the other hand other graftings on trifoliata are evergreen. Only this pot sheds its leaves.
I'll ask Sylvain if he has seen anything similar.

[Till]

Mikkel, I have P. polyandra from Darmstadt (a city near Frankfurt am Main) botanical garden. It is grafted on P. trifoliata and was always evergreen. But this year it looks like your plant: yellow and shedding leaves. I have other citrus plants that turn color, for instance Yuzu x Citrumelo on C35. I have no explanation, only a guess: The weather was too cool this year so that the roots did not produce enough auxin over a long time. That may result in color change and even deciduousness. But I am not totally convinced that my guess is right because my P. polyandra stands in a glashouse that was warm in summer. Warm but not warm enough? Or warm not long enough? Some seedlings did well in that glashouse (Citrumelo F2 and Cicitrumelos), others not.

Another idea is: Earth was too dry for a long time. But in my case that is not true. It was always moist.

[mikkel]

I have the polyandra from Darmstadt which is green as it should be. The polyandra from Horst is also still green. Only these two, of which I no longer know which origin they are, are losing their leaves. But they were actually very damp in the fall when it rained a lot and the saucers were literally flooded. That was a long time ago and long before they started to change color.
But at least that would be similar to your observation, could be a reason...

[bussone]

I have the polyandra from Darmstadt which is green as it should be. The polyandra from Horst is also still green. Only these two, of which I no longer know which origin they are, are losing their leaves. But they were actually very damp in the fall when it rained a lot and the saucers were literally flooded. That was a long time ago and long before they started to change color.
But at least that would be similar to your observation, could be a reason...

We may have to wait until spring and see what happens.

[usirius]

Well, it's not such a secret. I know the young man personally who visited the native region of Poncirus Polyandra in China over 20 years ago. He got some material from there, which he gave to a citrus friend to save and propagate. From there, some of the material ended up in the Damrstadt Botanical Garden (Germany). There are two types of Poncirus polyandra, which differ significantly in terms of leaf size and appearance. To illustrate this, I photographed both types side by side. Incidentally, as has been mentioned, Poncirus polyandra is more frost-hardy; for years I have been cultivating it outdoors with very little winter protection.

The origin must remain a secret but there are now several collectors who have them and a botanical garden in Germany also got them this way.
So far all the flowers are sterile and no fruit has formed

[bussone]

Incidentally, as has been mentioned, Poncirus polyandra is more frost-hardy; for years I have been cultivating it outdoors with very little winter protection.

I think this is the first time I've seen anyone state what polyandra's hardiness was.

[mikkel]

Hello usirius,

great that you have both forms. I've only ever heard that there are 2 forms and didn't know which form mine belonged to
I think I have the one with the smaller leaves. It also seems to be more like the one in the species description.

At the beginning I had a plant outside, but it froze back at -6°C, since then I've had it in a pot. How much has it survived with you?

In the photos it looks as if the form with the larger leaves occasionally develops monofoliate leaves. Is this the case or have the smaller leaves fallen off?
Have your plants already flowered? It has already flowered in Oer-Erkenschwick, but I haven't read anything about fruit yet. One of my plants is descended from this flowering one, but there have been no flowers here yet.

Thank you!

[usirius]

Incidentally, as has been mentioned, Poncirus polyandra is more frost-hardy; for years I have been cultivating it outdoors with very little winter protection.

I think this is the first time I've seen anyone state what polyandra's hardiness was.

I estimate that it survived -12 °C and showed no signs of frost damage.

Hello usirius,

great that you have both forms. I've only ever heard that there are 2 forms and didn't know which form mine belonged to
I think I have the one with the smaller leaves. It also seems to be more like the one in the species description.

At the beginning I had a plant outside, but it froze back at -6°C, since then I've had it in a pot. How much has it survived with you?

In the photos it looks as if the form with the larger leaves occasionally develops monofoliate leaves. Is this the case or have the smaller leaves fallen off?
Have your plants already flowered? It has already flowered in Oer-Erkenschwick, but I haven't read anything about fruit yet. One of my plants is descended from this flowering one, but there have been no flowers here yet.

Thank you!

The leafes are in geeneral trifoliat but this year the snails have increased in number and are eating the leaves on the young shoots, so that often one or two leaves are missing, then they appear bi- or monofoliate. Mine showed no damage, even in very extreme winters. I think you have a different variety or one from a different source if it has suffered major damage at -6°C. - They are not very fertile, but every now and then they keep a fruit, which they lose unripe in late autumn.

[mikkel]

I have several from different sources, but they are probably all the same. One is from Darmstadt. This was my first one and it was the one that suffered at -6°C.

[Till]

Usirius, that is interesting to know what a hardy P. polyandra you have. My small tree was also damaged at about -6°C. So the same experience as Mikkel. No wonder. We have the same variety.