Monday, 14 September 2009

OCAsional Update 1) To Bee Or Not To Bee

I think I made mention of the clumsy and unsophisticated pollination technique that I have used thus far on my ocas. As promised, I wandered the tractless wastes of the internet in search of enlightenment and inspiration. Well, I think I now understand a little more about the birds and the bees from the standpoint of my oca plants. In fact I have been keeping a tick list of pollinators I've seen on the flowers - no birds, but I have seen bumble bees and hoverflies along with a number of small dipteran equivalents of the twitcher's little brown bird.

My new technique involves what I can only describe as deflowering the maiden buds in the first bloom of youth. As unfortunate as this procedure is, I'm quite gratified by the results. There seem to be a number of pods setting and I can't help feeling that it's me and not the bees who deserves the credit.

Before I outline the whole sordid process, I suppose a few clarifications and caveats are in order.

1) An oca flower's season of youth is short. Flowers open between 9 and 10 in the morning here. Anthesis -that's to say pollen ripening - seems to occur a couple of hours later, around midday or in the early afternoon. The flowers then close up in the late afternoon. This is pretty much the same in many other Oxalis species. If they're not pollinated, then they open again the following day.

2) If it's too cold or dark or wet, they keep schtum - choose a nice sunny or bright day, if you're afforded that luxury. It can be hard to distinguish between a fertile flower and an unripe one when their petals are tightly furled.

3) You need to reconnoitre your plants to identify which plant has which stylar morph. Having ascertained which plants are which, tag or label them.

OK - let's pollinate some flowers.

Here's a short styled flower, which has the stigmas right at the base of the flower, with two whorls of stamens above it.

You also need to find a flower of another type, in this instance a mid-styled one, which has the stigmas in the middle, with stamens both above and below it. Good.

Now gently squeeze the base of the mid-styled flower with one hand so that the petals separate. Then grasp the bottommost petals with your other hand and gently pull. With luck and practice, you'll find that the petals come away.

I leave the top ones on as a bit of a rain guard, but if the whole lot come off, no matter. When I said deflowering, I suppose I meant depetalling. You should now be able to see the stigmas quite clearly and more importantly, gain access to them.

Make a mental note of the flower's position or mark the flower stalk with some coloured string. Wander over to your short styled flower and, repeat the process.

You now have two flowers, with different stylar arrangements and easily accessible stigmas.

The aim is to transfer pollen from one flower to the other. Easy, you say, with tweezers at the ready. Yes, but you need to transfer pollen from the anther which is at the same height as the stigmas in the corresponding flower. Like this:

And then reciprocally like this:

Confused? Let me put it another way. Take pollen from the bottom anthers in the mid-styled flower and put it on the stigmas of the short-styled flower. Take pollen from the anthers above the......

"If a picture paints a thousand words" - Could it be that dear old Telly Savalas was right when he sang those immortal lines? Let's see whether this helps. Here's a diagram:

It shows the possible permutations of what are called "legitimate" pollinations - the ones most likely to produce oodles of viable oca seeds. Illegitimate pollinations (you can work those out) are less likely to give rise to any viable seeds, but may be worth attempting when you're short of correct pollination partners and feeling tired, frustrated and hungry. It happened to me, folks.

So that's what you've got to do to ensure maximum seed set. I've yet to find a brush that's suitable for transferring the tiny quantities of pollen that oca produces, so I just pull off a stamen and rub the anther over the surface of as many of the correct
height stigmas as possible (five in each flower). If I can afford to be profligate, I'll do the same with another stamen. Sometimes I get a bit keen and the anthers haven't quite dehisced when I pick them. I'll give them a bit of a squeeze or stroke them very gently with my fingertip. If I see pollen grains on my finger, I'm satisfied that they're up and running.

I've just had a look at my friend Sarah's oca patch. She's not attempting any cross pollination of her ocas and yet I notice several pods are forming on her plants. I could choose to see this as a total invalidation of my pollination efforts. Actually, I consider this revelation to be encouraging. It means that when the right pollinators occur and the right varieties are grown under suitable conditions, then fertile seed can be produced. My suspicion is that oca pod formation is probably a more common occurrence than has been noted previously. The pods are, in all honesty, charismatically speaking, dull little structures, that might easily fail to impinge on the consciousness of any self-respecting grower. Here are some I found on 0917, which has styles in the mid position, hence the 2 in brackets.

That's oca pods at their most exciting. They fade to a dull yellowish brown and then treacherously flick their seeds out when you least expect it. You have been warned.


Catofstripes said...

Ha! you have flowers. Of the three types of oca I grow, two have never flowered for me and the third, the white form sold by Realseeds did flower last year but shows no sign of it this. Not that I care very much since it all looks like a lot of faff, but I'd like to have the option of not doing anything about it.

In fact, the pleasant hot and dry summer we've had in Normandy has left the oca and the ulluco looking a bit worn out. Might be a bad year for them altogether.

dogwooddays said...

Just identified my first flowers. Not sure I'm up to pollinating yet, but at least I understand the flower structure now so that's a start :-)

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