Sunday 20 May 2007

How to breed your own garden peas

Normally when a seed company is trying to develop a new variety they keep very quiet about how they're going about it, knowing that if they come up with something worthwhile everyone else will want to copy it.

There's no secrecy involved in the pea breeding project I'm doing for Ben and Kate at the Real Seed Catalogue. One thing I have in common with them is that we all believe passionately that genes, seeds and the skills involved in their production should be in the public domain. Unlike most seed companies they have extensive seed saving instructions on their website and I've been open about which varieties I'm crossing in trying to develop a new variety for them. So what's to stop anyone else copying what I've been doing? Absolutely nothing. And just to make sure you know how to, I'm going to explain hand-pollination.

The principles of making crosses by hand-pollination are fairly universal, and yet the details differ hugely from plant to plant. These instructions are suitable for all kinds of culinary pea, and will also work for sweet peas, and once you know what you're doing you can apply it to other plants. The basic principle is this: if you have a self-fertilising flower like a pea, and you want to cross it with something other than itself, you first have to remove its capability to self-fertilise.

So the first step is to emasculate the 'mother' flower by removing the little yellow blobs which produce pollen. That will leave you with just the female part, which is a long bendy green thing with a bristly bit down one side. With me so far?

Know your blobs from your bendy bits. The anatomy of a pea flower (with keel cut open)

Pea flowers have all their reproductive bits inside the keel, which is a sealed petal bag. The long green central bit is the style, but only the very tip is receptive to pollen. The pollen-bearing anther blobs gradually grow up towards the tip and shed pollen all over it. By removing the anthers before they get to that stage, you can intervene and fertilise the flower with the pollen of your choice.

The first step is to find a flower at the right stage. With peas that means using young buds, because their self-pollination happens very early on before the flower is anywhere near opening. The optimum stage is impossible to define precisely because it varies quite a lot in different weather conditions, and to a lesser extent between different varieties. The easiest time to do hand-pollinations is on a dry, cool, overcast day. On days like this the pollen is slow to shed (or dehisce, if you want the technical name) so you can get away with using larger buds which are easier to work with. When the weather is hot and sunny the pollen just goes nuts and splurges everywhere, so you have to resort to using only the youngest, tiniest buds. Windy weather is also a hindrance (try carrying a blob of pollen across a breezy garden on the tip of a scalpel blade and you'll see what I mean).

But as a general rule, choose buds where the petals are just about visible as they start to protrude from the sepals. The photo below shows a promising-looking bud.

Step 1: Peel open the bud ... gently roll back the sepals and the two outer layers of petals, and grasp them back out of the way. Inside you will find the keel petal, which is a sealed bag with a crinkly seam down the middle a bit like a cornish pasty. Using a scalpel or similar, carefully cut a slice in the keel. (You can remove part of it if necessary ... it won't do any harm.)

Step 2: As soon as you cut the keel open you will be able to see whether the bud has already self-pollinated or not. In an ideal bud, the anthers will be smooth dark yellow blobs with no traces of yellow powder on them, and will not yet have grown right up to the tip. Being careful not to damage the long green bendy bit in the middle, hoik out all the yellow blobs and pop them off with the scalpel blade. There are ten of them and it's best to remove them all.

If the anthers look fluffy or there is yellow powder inside the keel, it's probably too late. If in doubt, have a look at the tip of the green bendy bit. If it looks pristine it should be OK, but any trace of yellow stuff on it means that self-pollination has already happened.

Step 3: Mark the bud by tying a scrap of coloured thread around its stalk ... not too tight, to allow it room to grow a bit.

Step 4: Find a pollen source on another plant, of whichever variety you want to use as the 'father'. Again you may need to do a bit of poking about with a scalpel to find one with lots of pollen to spare, as it varies with the weather. The best ones are usually larger buds which are almost ready to open. Slice open the tip of the keel and scoop out as much as you can onto the blade. This will not harm the flower at all, because it will already have self-pollinated and started growing a pod ... all you're doing is making use of the surplus pollen. Fresh, fertile pea pollen is a deep rich yellow colour. If it's turned a pale sandy colour it's too old.

Step 5: Take the pollen to the 'mother' flower and gently slather it all over the tip of the green bendy bit. The receptive part is the stigma, which is the flattish area right at the tip. Please note, the stigma is NOT the bristly brushy bit just below the tip ... it may look like it should be, but it isn't.

It can be a bit fiddly to get the pollen in the right place but it gets easier with practice.

Step 6: If the remains of the keel petal are still intact, slip it back over the green bendy bit to give it some protection and help stop the stigma drying out. It's not essential though ... you can get away with just closing the outer petals back over it.

The flower should then open pretty much as normal over the next few days, and shortly afterwards you will get a pod. While the pods are small they are translucent against the light, so you should be able to see the baby peas inside if the pollination was successful. If it wasn't successful the flower will drop off.

In peas, it's quite usual for hand-pollination to have a lower success rate than natural self-pollination. So don't worry if your hand-pollinated pods only have two, three or four peas inside them. That's normal.

If you're looking to possibly produce a new variety, it's a good idea to hand-pollinate quite a few flowers ... at least 20. You don't need to do them all at the same time ... just do three or four a day for as long as the plants are producing good flowers. Allow the pods to develop fully and harvest them when they've started to go dry and crispy (in wet weather you may have to grab them earlier, to avoid problems with mould). Hang them up in a dry airy place to finish drying. You now have your own unique F1 hybrid peas. When you grow them they should produce plants with a mixture of characteristics from both parents.


I need orange said...

I love reading about all this......

Anonymous said...

Terrific post Rebsie, I have followed your adventures here and you have inspired me to try breeding peas. Only trouble is I have no idea what I would like to cross with what so another bright idea down the drain.
In the meantime you have also convinced me to try the Alderman pea. I have a supply coming over in a week or so and will plant them for a late crop. I am eager to see if they are as good as you say. I am in Bulgaria so no trouble about cold weather.
Many thanks for your work here.
BTW, if you need some of your f3’s (or will it be f4’s?) grown for seed next year, I can offer plenty of space well away from other pea crops.

Rebsie Fairholm said...

Thank you both for the comments!

Phreddy ... I don't always have much idea what I would like to cross either, and I don't think it matters much ... nothing wrong with a bit of pot luck! I started off just crossing whatever varieties happened to be in flower at the same time. Do let me know how you get on with Alderman ... it's still my favourite pea and I'd be interested to know how it copes with the climate in Bulgaria. Thanks for the offer of some growing space ... I may well take you up on that as I'll soon have too many breeding projects to grow them all in my own garden. My sister-in-law is Bulgarian and some of the vegetables (peppers, beans etc) her mother has sent over to us have been incredible and I wish I'd saved seeds from them. If you ever want to do a seed swap and send me some traditional Bulgarian seeds in exchange for any of the things you've seen on my blog please let me know!

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Elliott Broidy said...

Interesting. I wanna give this a try.

Generic viagra 100mg said...

oh wow, i love the way you have explained about the breeding and growing pea garden. Pea flowers has there reproductive inside. I didn't even know about the hand pollination, of course as i m not a gardener. And never even tried that.

rolf.parkerhoughton said...

Thank you for this excellent guide.

I am helping reintroduce two peas to our community,peas that were grown here as early as 1804. We are working with the local schools.

My question is, can you breed together peas as different from each other as Tall Marrowfat, and Early Frame?

Early Frame, of course, is early, and Tall Marrowfat is prolific, so the mix would be tempting, but the little I have read suggests that they are very different sorts of peas. My question is not so much if this is a good pair to try to breed together, but rather, is it even possible ?

scamworm said...

I am doing a sweet pea breeding project at Davis, and this was very helpful. Thank you!

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