ProMusa discussion forum

Posted by hugo volkaert on 31 Jan 2012 08:06

I think these plants are hybrids between Musa acuminata and M. laterita. During my trips in the area, I have found similar plants at various locations, I have tested the chloroplasts of one of them, and it turned out to be an acuminata chloroplast, suggesting that the female parent of the specimen I analysed is a local Musa acuminata ssp burmannica/siamea. I have not done more molecular work on it.

There are several morphological characteristics that would indicate a possible hybrid origin. The colour of the bud is intermediate between the purplish red of the acuminata subspecies siamea/burmannica and the orange of laterita. The size of the plants is also intermediate. The rachis is not erect as in laterita, but also not pendulous as in acuminata... it is in between. I did not dig out any rhizome, but the drawing the authors provide in their article also suggests that it could be intermediate between the two species. The authors show a picture of seeds, but they do not say whether they are viable. The fruits of all specimens I have observed were almost all badly shaped, only partly filled with a few seed. All seed I have checked were "floaters" while a fully developed seed will sink.

It is unfortunate that the authors do not include in their article a discussion on the possible place of this new species within the genus Musa, i. e. whether it belongs to the section Musa or Rhodochlamys. Several molecular analyses have indicated that both sections are not very well separated. If indeed this species is the result of a hybridisation between M. acuminata (Musa section) and M. laterita (Rhodochlamys section), it again indicates the problematic status of the two sections as separate.

It would be interesting to compare serpentina with Rhodochlamys species such as M. rubra, M. rosea, and M. chunii. All are poorly described and have been found in the area between Thailand, Myanmar and Southern China, probably occurring also NE India and Bangladesh. Musa rubra was described by Kurz and the specimens are in Kew herbarium. The lectotype was collected in Myanmar. If I am not mistaken, AFG Kerr also collected M. rubra in Thailand.

A few nuclear gene loci together with a chloroplast marker would greatly help teasing apart the species from the hybrids.

I attach a photo of the plant on which I checked the chloroplast. It was collected in 2006 and is kept at the Chiang Mai University Herbarium.

Posted by Markku Häkkinen on 31 Jan 2012 21:00

In my opinion it is a natural hybrid between M.acuminata and M.laterita. It has characteristics from the both species so it is easy to clarify as a hybrid based on its morphology. In addition these two species are growing synpatrically.

We managed to grow many similar kind of hybrids in our botanical garden collection by hand pollinating / crossing the Musa acuminata and Musa rubra plants some 8-10 years ago.

Simmonds mention also in his book "The Evolution of the Bananas" on page 66: point 4. ACUMINATA x LATERITA. Geography - very probably in lower Burma; crossing is very easy, both ways; germination good; hybrids (A x L and L x A ) vigorous. (Tested in Trinidad).

There are several Musa rubra specimens at Kew collected from Thailand and lower Burma.

What is coming Musa chunii it occurs too far a way from Thailand and I have found it only in one location in China despite of several years field study in Yunnan.

Posted by Markku Häkkinen on 01 Feb 2012 10:40

The correct name should be Musa x serpentina. However, as it is validly published it can be only changed in the new article as comb. nov.
This should need to study the plant in its natural habitat.

Posted by hugo volkaert on 01 Feb 2012 11:19

I agree with Markku that the name most likely will have to be changed to Musa x serpentina... but before doing so some investigation is warranted. Several plant species are of hybrid origin, nevertheless they are valid species. So, even if this turns out to be a hybrid (I think it is very likely, but needs to be demonstrated), then still it needs to be shown that this plant is just that... or that it is a new species of recent hybrid origin.
The fact that only few seeds were obtained by the authors (and similarly, I have not found any good seed set in these kinds of plants) would lead me to believe that most of the plants among the hybrids are an evolutionary dead end... no reproduction possible. If on the other hand reproduction is regular, then it should indeed be maintained as a new species.

Posted by Sasivimon Swangpol on 03 Feb 2012 19:00

Thank you for your interesting comments on our new banana species. We, earlier, also had doubts quite similar to yours so we did some experiments before we published it.
As you said, many goods species are hybrids, wheat is one example and I’m sure there are many more. In fact, how would a species originated if it was not once a hybrid, and by chance, has survived? Our plant maybe a hybrid, but we are certain of its specific status. You could try the key again and if it doesn’t clearly distinguish the plant from the related species, then you are welcomed to correct its name. Anyhow, this is science, it’s not a law.
I wonder how you would say what characteristics is “intermediate”? Can you really say “pink” is between red and orange, or medium height is between short and tall? There’s no such an easy thing like that in biology, I do think. More info on the height, this sp. nov. is vigorous, almost as tall as balbisiana. It may contain balbisiana genome, who knows :D?
Another thing about its seeds, they are viable. I have attached herewith a photo of one of its seedling growing in our greenhouse.
About sections, I thought it should have been realized long time ago (since say, Wong et al 2002) that the sections in Musa are invalid, at least for the Rhodochlamys and Musa sections. I completely agree with you that we cannot distinguish between the two sections, therefore there’s no need to mention about it. This species is a good example showing overlapped characters found between them, so let’s drop the sections!

Posted by Sasivimon Swangpol on 03 Feb 2012 19:26

Back to the specific status of this serpentina, we carefully investigate its morphology and did AFLP analysis, which I attached the result. You can see that sp. nov. separates well from others in the tree and also by several key characters in the manuscript. We are doing SSR and DNA sequencing and will let you know of the results soon.
P.S. Banana in your photo attached has two rows of fruits, so it’s different. If you say you found both one and two rows in a species in nature, pls send photos. It will be very interesting to see.

Posted by hugo volkaert on 06 Feb 2012 06:21

It is great that you could obtain 1 (one) seedling. It's morphology will be a good clue as to whether its parents are hybrids or not...

As far as the AFLP analysis is concerned, it is very clear from many studies in cultivated bananas that the AAB and ABB hybrids clearly separate from the A and from the B parents. So the fact that the Musa serpentina samples group together in a separate cluster closely linked to M. acuminata and M. laterita (and far from M. balbisiana) is not a proof of its specific status - nor of its hybrid status. A hybrid is the result of the merging of two evolutionary lineages. AFLP analysis combined with distance matrix calculation and UPGMA or Neighbour Joining, can only combine groups two at a time. Or, looking at it from the "Root" of the tree, from one ancestral (extinct) sample, it splits up in two derived (extant) samples. In case of a hybrid, both ancestral parent species are still existing, and included in the analysis, together with their hybrid derived progeny. This can never be depicted in a UPGMA or NJ clustering phenogram, because it would imply grouping the hybrid together with the two parents, and the parents should be both at the node and at the tip of the branch. This is different from an unresolved phenogram, where three or even more taxa can share one single common ancestral node! Mind though that if you would get an unresolved result with all three taxa having one common ancestral node, that would not be any better argument for hybrid status.

Concerning the traditional sections within the genus Musa, it is true that Wong et al. have obtained molecular data that confirm the doubts that already existed about the separation of section Rhodochlamys from section Eumusa / Musa. Markku Hakkinen has recently published the lectotypes for the section Rhodochlamys, making it more "official" in botanical nomenclature than it was before. Hakkinen 2009. Lectotypification of two Musa sections (Musaceae). Nordic Journal of Botany 27: 207-209.
If Musa serpentina could be clearly shown to be indeed a hybrid, it provides more arguments for the merging of the sections Musa and Rhodochlamys... but for the time being the sections still exist, and thus and reference to them is still valid - or since the Hakkinen publication, even MORE valid.