Friday 9 August 2019

Red-podded pea update: the F6 crop and beyond

Ever since I first had a red-podded pea turn up (completely unexpectedly) in a breeding project in 2008, I’ve had a bit of a frustrating time trying to get it into a form which is worth releasing into the world. Not that I’ve been trying continually, because I haven’t been able to maintain the garden every year during the last few years, but it has had me scratching my head trying to come up with a way of producing edible pods with this rich crimson colour. Finally, in 2019, I had a significant breakthrough.

The original red-podded pea plant, numbered GSC 15 in my breeding project, was an F2 from a cross between Golden Sweet and Carruthers’ Purple Podded. The purpose of the cross was to breed a new purple mangetout pea for Ben Gabel at Real Seeds, but neither Ben or I had any idea that crossing a yellow pea with a purple one would result in a red colour. It was only this one plant which produced red pods, and it happened because it was a yellow-podded pea with a solid layer of purple pigment on top. The pigment is translucent, so the yellow shining through from under the purple creates a beautiful glowing red, like stained glass.

This breeding line, which is currently somewhere around an F6 or an F7, is now a stable, true-breeding variety. It’s reliable and consistent for all its traits, except one: it still turns up a small minority of offspring whose pods are not fully red. It doesn’t tend to throw any plain yellows any more, at least not in the growouts I’ve done, but it will produce some semi-red plants which look like the red pigment has just been sprayed around the edge, and some which have a jagged, flamed pattern of solid red on a yellow background. I think these are caused when one or other of the two dominant genes for purple pods is unable to express itself. But WHY it can’t express itself I don’t really know. All I know is that it happens often enough to be a thing, and on that basis I don’t think the semi-reds will cease appearing no matter how many years are spent trying to rogue them out. They just have to be accepted as the nature of the beast, and besides, I had one semi-red this year which I liked enough to want to keep it, if I can persuade it to become a variety in its own right.

One of the semi-red phenotypes. I believe it's probably caused by co-dominance between purple and non-purple genes. Because of that, no amount of 'roguing out' will eradicate these oddities, which show up in a small minority of offspring.

But anyway, having reached the F6 generation this stable red-podded variety still has a problem, and the problem is not going to go away. It doesn’t taste good, either as a shelling pea or a mangetout. It has a gristly layer of fibre inside the pod which makes it unsuitable for eating even when it’s small, and if you shell out the peas to eat fresh they are starchy as hell, with a bitter aftertaste. The genes controlling flavour in peas are complicated, but the situation here is very simple – it is true-breeding for crap flavour.

It does, however, look truly stunning.

It’s possible that it will find a use as a soup pea, maybe becoming edible when it’s dried and then boiled for ages. The jury’s still out on that one. But in its current form it’s not suitable for unleashing on the world, and will have to be considered a breeding line. To that end, I grew out a batch of seeds in 2019 which had been in storage for 4 or 5 years, just to replenish my stock of seed. I saved seeds from the best ones (which was most of them, as it’s certainly a fine-looking variety) and saved the rest for taste-testing in the kitchen, some time when I can be arsed to boil up a vat of pease pudding.

So, what to do? I need red-podded peas with edible pods. And ones which taste nice.

When I did my initial report on the edible-pods frustration nearly ten years ago, I said there were five things I could do about it. Here they are again, with the results of my efforts.

1. Stand in the middle of the garden and shout "BOLLOCKS!" in a really loud voice. Yep, done that.

2. Grow out the remaining F2 seeds (about 20 left) in the hope of finding another red-podded phenotype but with edible pods. This didn’t provide what I was looking for, but I did find an extremely nice purple mangetout (the whole point of the breeding project in the first place) which I selected and re-selected in the F3 and named Barcarolle.

3. Grow out the remaining F1 seeds to get more F2 seed. I tried this, as part of a belt and braces approach. Growing out more of the F1 took a year but it yielded plenty of seed. I grew a batch of F2s in 2019 and some of them were quite nice but no, I didn’t get the tasty-edible-red-podder I wanted.

4. Switch to another line of F3 seed, even though none of them are proper red-podders. This was always a good bet, because some of the necessary traits for red mangetout pods are recessive genes which may be hiding in the DNA of a plant which isn’t showing it. For example, yellow is the base colour for red pods and you can’t get red pods without the recessive ‘golden pod’ gene known as gp. The laws of probability suggest that two out of three of the F3 lines should carry the gp gene, even though they don’t themselves have yellow pods. Also, the two genes which produce edible (fibreless) pods are both recessive, so a goodly proportion of inedble-podded lines could produce edible-podded offspring.

Although only one of my original batch had properly red pods, I did get a couple of peachy-coloured or semi-red mangetout lines. My efforts revolved around these, as they were so “nearly there” – they had sweet-flavoured edible pods and a beautiful fiery blush. But sadly the fully red colour didn’t show up in their offspring either.

But although I didn’t get anywhere with the ‘peachy’ F3 lines, it was another F3 line which gave me my breakthrough in 2019, in a completely unexpected place: my Barcarolle purple mangetouts.

5. Grow more of the original red-podded F2 and cross it with something else. I tried a lot of this as well, but it's the most time-consuming option and I don't have many results yet, so I’ll report on it another time.

Barcarolle purple mangetout
Right then, this is what happened with the breakthrough. Alongside my growout of red-podded peas this year, I planted 16 seeds of my newly developed purple mangetout. Sixteen plants is not very many, but I’m doing all my breeding work on a very small scale in my back garden, so that’s all I have room for.

Barcarolle is a very promising variety which originated from the same cross as the red podders – Golden Sweet x Carruthers’ Purple Podded. I selected an F2 plant a few years ago which had beautiful dark velvety purple pods – a really solid dark purple, which is not something you get all that often in peas. As the peas start to swell inside the pod, they bulge through the pod wall and look like a row of little blackcurrants. The reason this happens is because there’s no fibrous membrane inside the pod, like you’d get with a shelling pea. It takes two recessive genes to get the pod walls completely fibreless like this, and it’s a desirable trait to have because it means the pods are fully edible at all stages of development – they don’t go coarse and gristly. I also got lucky with the flavour, as the pods tasted sweet and juicy and were pretty much stringless. Again, this is an uncommon thing to find in a purple-podded pea, because the purple colour is often associated with a slightly bitter flavour. It’s not that the pigment itself is bitter tasting, but there’s some kind of gene linkage going on which means that the purple pod genes are usually inherited alongside some less-desirable flavour genes. This was by far the best purple podded pea I’d ever tasted so I was well chuffed with this plant.

The following year I grew out the F3 generation, and to my delight, it came almost completely true to type. I had expected a few unwanted recessives to show up, but they didn’t. The F3 plants were as uniformly purple and bobbly and sweet and juicy as the previous year’s plant. I don’t always name my breeding projects at this relatively early stage, but it seemed like it was going to be quick and easy to make it into a stabilised variety so I gave it the name Barcarolle. (In case you’re wondering, I play the piano and I’m a big fan of Chopin.)

So then I grew out this batch of F4 plants in 2019, and, well, to say they began to segregate is an understatement. They segregated like buggery. Fortunately they all had the bobbly edible pods (a recessive feature), but they varied in size, flavour, number of pods per node, and most of all they varied for pod colour. In my batch of 16 plants, I ended up with four different pod colours – purple, green, yellow and red!

My 2019 crop of Barcarolle F4 purple mangetouts, segregating for four different pod colours ... aaargh!

I must admit I don’t quite know why this happened. It doesn’t make sense for a variety which is true-to-type in the F3 to suddenly start segregating like mad in the F4. The most likely explanation, I think, is that I happened to grow out (by chance) only seeds which were heterozygous for pod colour in the F3 generation, so they all showed the dominant purple colour but they still had the recessive genes squirrelled away in their genome. Given that I work with such small sample sizes, this is entirely possible. But anyway, who cares – the thing that matters is that I ended up with no less than four red-podded plants, all of them with lovely juicy edible pods. This is such a holy grail for me, some 13 years after I made the original cross, that I spent an awful lot of time just standing in the garden gawping at it.

The purple pods on the left are what Barcarolle is supposed to look like, but it came out with these red podded variants as well.

In some ways I probably shouldn’t be surprised to be getting red pods segregating out from Barcarolle. The only difference between red pods and purple pods is the base colour of the pod – green for purple-podders and yellow for red-podders. Barcarolle is derived from a yellow-podded parent, so the presence of the recessive gp (golden pod) gene shouldn’t be a surprise. I might have saved myself some grief if I’d tried looking for it here earlier.

As well as being exactly what I’ve been looking for for the last decade, the Barcarolle red-podders have some other advantages over my original red-podded pea. The red colour itself is a bit brighter – more scarlet than crimson. Both colours are equally nice when the pods are young, but one slight flaw in the original variety is that the red tends to darken as the pod matures, until they start to look purple rather than red. The reason for this is not a change in the pigment itself, it’s because of the natural darkening of the base colour of the pod. As yellow pods age, they tend to go more green – a trait seen in the parent variety Golden Sweet – and a greener pod means the pigment appears more purple. In the Barcarolle-derived red-podders, the pods stay yellow right through to maturity, and so the pigment continues to look red for a lot longer. I don’t know what subtle genes are responsible for this difference, but it was consistent across all four of the plants in this batch.

The best of them was the plant known as BRC 16 (above), which was hugely productive. It grew to around 7ft tall and not only produced two pods per node, it also developed fully productive sideshoots – a rare thing in peas – and bore good quality pods on those as well. It also did very well in the looks department, having beautiful colour-changing flowers borne on stems with a lot of bright scarlet colour and pretty pink mottling on the calyx. BRC 14 and BRC 06 were both very similar but not quite as vigorous. The best one for flavour was BRC 11 which had a fantastic juicy raw flavour, like apples! 

I do want to develop a red-podded pea which tastes good raw, because the colour is spoiled by cooking. With any red-podded or purple-podded pea, if you cook it any way other than the lightest steaming, the colour just disappears into the cooking water. No amount of careful breeding is going to resolve this, because it’s in the nature of the pigment itself – anthocyanin, which is water-soluble, and that’s just the way it is. So the only thing a plant breeder can do to get around this is to develop varieties which taste so good raw you won’t need to cook them.

Now, of course, I will have to wait until next year before I can grow out the offspring and see how they look. But I’m very optimistic. And I still have the purple-podded Barcarolle line which, once I’ve stabilised it, will be a wonderful variety in its own right. The red-podded line is not named yet, but I have another year or two to think about it.

The Barcarolle-derived red peas have beautiful bicolour flowers which turn blue as they fade, like these on BRC 16.


Triffid said...

Thank you for posting this Rebsie, and congratulations on your breakthrough!

I've been following the red-podded saga for a while and your blog is what got me into plant breeding myself.

The Barcarolle lines are truly stunning, well done :)

Rebsie Fairholm said...

Thank you – if I've helped in any way to inspire you to take up this wondrous plant-breeding lark, then that makes me very happy.

Jeremy Cherfas said...

Incredibly happy to see your site pop up in my RSS feed reader. That you were testing ancient tomato seeds that happened to germinate makes the whole thing more than mere coincidence. Anyway, so pleased to learn of your progress with the red-podded mangetout. I only wish I still had garden space.

Rebsie Fairholm said...

What a lovely comment Jeremy, thank you so much. Your support and encouragement have always been enormously appreciated so I'm very glad to hear from you.

Patrick said...

Great to hear from you again. Nice to see you're still gardening and still working on this pea. Hope to hear more.

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Philadelphia Gardener said...

Just so cool, Rebsie! So great that you have a gardening space again and are growing!

keen101 said...

Haha! I'll definitely need to try option number 1!

Rhizowen said...

Peas are like good friends - you have to forgive them their little foibles. Glad to see you're making such good progress. There's something incredibly familiar and comforting about growing peas, as well as something strangely enigmatic and exotic in their demeanour too. I blame those tendrils. I could study them for hours.

Nathan said...

Great to see the Red-podded pea project still on the go. Awesome work Rebsie.

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Jude said...

Hello - hope you are doing well? These two varieties are stunning! We swapped some seeds back in the day and I also liberated some of Dave's seeds on the Homegrown Goodness forum. I passed loads of them onto the HSL Library and they have just re-introduced them for all. Antyway I hope all is good with you :-) Jude (barkingdog)

Anonymous said...

Lovely to hear and see your progress. You have inspired me in Australia to do the same. Hopefully without the crappy flavour and texture. My first red podded pea is just coming on today! file:///var/mobile/Library/SMS/Attachments/42/02/48A54C7A-E79F-4AE4-A8E1-E82A3205E585/Screenshot%202023-08-25%20at%204.38.26%20pm.jpeg