Pin, Thrum and Pollination

[Lesley Cox]

Next they'll be separating off many Primulas into subspecies because some are pin and some are thrum eyed!



Edit: This post and a number following derived from this comment made by Lesley in the Crocus February 2008 page, after some talk of taxonomic changes... lumping and splitting, as we call it...This lead to these posts which were a distraction on the Crocus page and so have been moved here tothe Primula section instead!     M.
 

[Anthony Darby]

Pin and thrum is how primulas of the same species avoid self pollination. I could bore you with the details....

[David Nicholson]

Pin and thrum is how primulas of the same species avoid self pollination. I could bore you with the details....

I think we knew that, but does 'pollination' sometimes have one 'l' and little green marks??

[Martin Baxendale]

Pin and thrum is how primulas of the same species avoid self pollination. I could bore you with the details....

I think I read somewhere that you can't pollinate a pin-eyed primula with pollen from another pin-eyed primula, or a thrum-eyed with pollen from a thrum-eyed. That to get good pollination you need to cross pin-eyed with thrum-eyed and vice-versa. That would mean there are structural differences between the pollen and stigmas of pin-eyed and thrum-eyed that make self-pollination difficult. Would that be right, Anthony?


Edit by M. : post from Lesley Cox in reply: February 19, 2008, 09:08:53 PM-------------------------------------------
In which case (structural differences) why not one a subspecies of the other? I'm playing devil's advocate here.

[Tony Willis]

I am trying to remember back in the mists of time to primula aureata in which there was only one form in cultivation (pin)and I think that with perseverance some seed was produced which resulted in both pin and thrum being in cultivation. At about the same time somebody put pollen of another species on a pin plant which them produced fertile seed which produced plants identical to the parent(not hybrids)  in both pin and thrum and again further off spring plants were produced.

[Anthony Darby]

Yep. Apart from the positioning of the stigma and anthers to enable pollen to be at the correct place on the insect, there is  a sort of barrier with different 'mesh' size in the stigma which prevents the wrong pollen sending a tube down through the style. Large 'mesh' in a pin flower style allows both pollen to 'germinate' and grow down, but as thrum pollen is larger and grows faster, pin pollen fails to reach the ovules. In thrum only small pollen from pin flowers can germinate and grow down through the style.

   

[Martin Baxendale]

I am trying to remember back in the mists of time to primula aureata in which there was only one form in cultivation (pin)and I think that with perseverance some seed was produced which resulted in both pin and thrum being in cultivation. At about the same time somebody put pollen of another species on a pin plant which them produced fertile seed which produced plants identical to the parent(not hybrids)  in both pin and thrum and again further off spring plants were produced.

Tony, it sounds like the second case may have been something to do with apomixis, where seed forms without sexual fertilisation and produces seedlings which are genetically identical to the parent, or self-pollination where the foreign pollen somehow turned off some of the anti-self-pollination mechanisms so that self-pollination became possible- or perhaps a bit of both?

[Tony Willis]

martin

it was a long time ago but I think those were  explanations given at the time.

Mrs W. is now wondering if that is how our two off spring came about!!

[rob krejzl]

Richards says that the original P. aureata introduction by Bailey consisted solely of pins, with the thrums coming in as a subsequent, separate, introduction. All seed set from the first introduction gave rise, of course, only to pins.

[Tony Willis]

Richards says that the original P. aureata introduction by Bailey consisted solely of pins, with the thrums coming in as a subsequent, separate, introduction. All seed set from the first introduction gave rise, of course, only to pins.

I do not doubt John Richards source but I do not think this is necessarily correct and may be a case of you do not know who you do not know to misquote Mr Rumsfeld. I knew a man long since dead who was quietly raising P. aureata from his own seed from one original plant 35 years ago and giving them away locally to friends. The accepted theory at the time was that they would not set seed on their own pollen and it was only comparitively recently that seed raised plants have been widely available.

[rob krejzl]

Of course, we can never be sure of what the original introduction was. It may have included pins and thrums. But since the production of seed by pins without thrum pollen can happen (if rarely), the production of seed doesn't by itself mean we have any evidence for thrums being present. Was your friend setting seed on a single plant getting both pin and thrum offspring? Had he eliminated any chance of hybridisation?

[Tony Willis]

Rob

I am going back a long time but he only grew the one petiolarid primula so there was no chance of the off spring being a hybrid.I did not know at the time I would be asked for more detail or I would have taken more notice at the time. It was 35 years ago and I was just in awe of his skill and almost afraid to speak in case I showed my ignorance. What I know is that he originally had only a single plant.

[Diane Whitehead]

Primlets, acaulis with wavy petals, are all pins.  I've checked the ones being
sold here, and they've been checked in the U.K. as well.

I've just done a quick skim of John Richards chapter on the evolution of
heterostyly, and it says that P vulgaris is pin x pin fertile but that only 60%
as much seed is produced compared with pin x thrum.

I wonder if the pins are deliberate - to make it a bit harder for people to
grow their own.  Though I've only had primrose seed when I have pollinated
the flowers - they don't set seeds on their own in my garden.  Also, I
imagine that most of the pretty plants are kept in their pots and tossed out
when they finish blooming.  They produce a lot of flowers.  I bought mine
over a month ago and there are still lots of buds emerging.

Or perhaps the rosebud form comes from a gene linked to pins.

They were bred in Japan by Kirin Brewery.  I think it was also Kirin that
developed a rosebud acaulis about 20 years ago.  They were distributed at
Primulas Worldwide, which was put on in Portland Oregon, U.S.A. by
primula societies from Japan, the U.K. and the U.S.  They did not persist
in our gardens, and we decided they had been developed for use as pot
plants. I did not notice whether they were pin-only.

[Paul T]

Diane,

We have the same series here, under the name "Rozanne" series, or something like that.  The more I think about it the more elusive the name becomes, so it is probably a name nothing like that at all!!    That same semi-double look on what is essentially a single flower with wavy petals.  I find they don't last well here through summer, unlike some of the polyanthus which go through just fine.  Nice flowers though, and worthwhile growing, that is for sure.

[ashley]

Revisiting this thread reminds me what a great resource the Forum is

So do I understand correctly: thrum x thrum crosses are impossible while pin x pin crosses are less fertile and can produce only pins?

And in the latter case, is there a decline in vigour?