Monday, 14 January 2008

Summary of the Purple Pea Project 2007

And when I say "purple peas", I ain't kidding!

This is just a general update on my progress with the peas so far. In my usual disorganised fashion I've ended up with two main projects and a large number of sub-projects, but that's all part of the fun.

Before I start, I'd better reiterate what I mean when I talk about F1 hybrids. When two distinct varieties of a plant are crossed, F1 is the term used to describe the first generation of seed resulting from that cross. It stands for "first filial". When the F1 plants are grown, the seed they produce is called F2 (second filial), and so on. F1 plants tend to be very uniform because their genes are a fairly straightforward half-and-half combination of both parent types. But in the F2 generation the genes are randomly recombined and all sorts of different traits start emerging. That's why the received wisdom dictates that you should never save seed from commercial F1 hybrid varieties, as they won't come true to type. But that's exactly why they are so valuable to plant breeders ... every F2 seed is potentially the basis of a new variety.

Biologically speaking there's no difference between an F1 hybrid made by a gardener for breeding purposes and the F1 hybrid varieties you see in garden centres and seed catalogues. The difference is in how they're used. Seed companies sell F1 hybrids as varieties in their own right, because they make way bigger profits than non-hybrid seed ... not least because you have to go back and buy it again next year if you want to carry on growing it. Whether these commercial F1 hybrids are in any way better than standard open-pollinated varieties is open to debate ... in my own opinion they're overhyped, largely a waste of money and potentially very harmful to long-term biodiversity. But that's a topic for another post! From a plant breeder's point of view, an F1 hybrid is an exciting opportunity to mix up a whole load of genetic material and see what you end up with.

My pea breeding endeavours in the 2007 season had two phases. The first was to make crosses by hand-pollinating my chosen varieties. The rest of the season was taken up with growing out F1 hybrids. My F1 seeds were from the crosses I made in 2006, but I also managed to re-plant some newly harvested seed from the crosses I made in early 2007 (i.e. two generations in one season). It was only the projects based around Golden Sweet that matured quickly enough to squeeze two crops into one season. Alderman is a late maturing variety and doesn't have time to complete a late-season crop before keeling over with mildew, so it's better to be patient and grow one generation a year. Peas are one of the few vegetables you can do the two-generations-in-a-year trick with anyway, because they fulfil their lifecycle in a fairly standard timeframe regardless of when you plant them (within reason). Peppers, tomatoes, onions etc rely on having a proper 'season' and are senstive to changes in daylength, so it's no good growing them outside their proper time.

Another subject of debate is whether F1 hybrids really do have hybrid vigour. I recently attracted some criticism on a plant breeding forum for suggesting that naturally inbreeding plants (such as peas) don't show hybrid vigour, at least not to any significant extent. My own experience is that some crosses show hybrid vigour in an obvious way and others don't, but either way it involves such an elaborate range of factors there really is no precise scientific way of measuring it. With Golden Sweet x Sugar Ann it was pure vigour ... the plants were huge and grew like rockets. Others had more subtle ways of expressing it, in their elegance and beauty or their hardiness. But a number of others just seemed to take after their least-vigorous parent.

Although flavour is one of the most important factors I'm looking for in a new pea, at this stage none of the hybrids are being tasted or assessed for flavour. There's not much point, because the genes will not start to reshuffle properly until the next generation. Any special qualities in the F1 plants are for this one generation only, and their progeny will all be different. Besides, the peas are far more valuable as seed stock, as each one of them has its own unique genetic possibilities. The breeding work really starts with the F2 generation, so the main purpose of the F1 plants is to produce as much F2 seed as possible.

The crosses I've made so far are quite diverse, but the project mainly centres around two principle varieties which have been used as mother plants.

Alderman (click here for pictures)
A very large and luxurious variety of white-flowered, green-podded pea. So far none of the hybrids I've made from it have matched it for pod size, pea size or flower size, though environmental factors may have contributed to this as the hybrids were grown late in the season, and I haven't found Alderman to be well suited to late season cropping, it does best when allowed to flourish slap-bang in the middle of the year. Its real trump card though is its knock-out flavour, which it retains even when the peas have reached a huge size. So flavour will have to be monitored in future generations. It's probably the interactive result of a number of different genes so I don't expect it to be easy to maintain it.

Golden Sweet (click here for review and pictures)
Golden-podded, blue flowered, speckle-seeded and gorgeous, this one was given to me by Ben at Real Seeds to use as the basis for a new mangetout variety. There must be a lot of dominant genes in it because all the hybrids I've made from it have been pretty close matches to the mother plant in every detail. Except – the yellow colour. That is totally absent from all the hybrids. Not a trace of it. I knew the "yellow" gene was likely to be recessive, and this is as good an example as any of how a recessive trait will totally vanish from the F1 population.

Ideally when crossing plants it's a good idea to make the cross both ways, so each plant has a chance to be a seed bearer and a pollen provider. In some cases though that isn't possible because of variety differences. Purple podded pea Desiree is so quick to shed pollen I found it almost impossible to find flowers in a virgin state ... even the tiniest newly-formed buds had already self-pollinated. Earliness of pollination is something that varies from one variety to another, but it's also affected by times of day, weather and seasons, so it's not a precise science. You just have to get used to the individual quirks of the peas you're working with. At the opposite end of the scale, Ne Plus Ultra was an absolute doddle to hand-pollinate, always very obliging.

Splodgy pod, courtesy of Mr Bethell's Purple Podded x Alderman (F1 hybrid)

Here are some brief notes about the various crosses I'm working with, i.e. the ones I've actually grown. Some of them were interesting enough that I'll do a whole separate post about them. I made many more F1s which I haven't grown out yet.

Alderman x Kent Blue F1
Green pods and white flowers. Doesn't have many obvious Kent Blue traits at the F1 stage. It looks like Alderman, but nowhere near as vigorous. The F2 seed does look interesting though, with a mix of colours and round/wrinkled types.

Alderman x Carruthers' Purple Podded F1
A cross between what are probably my two favourite pea varieties, and the F1 hybrid showed many of the best traits of both. The pods are beautifully marbled and mottled with purple and green. This marbling is quite common in a hybrid between a green-podder and a purple-podder (probably co-dominance of the respective colour genes) but they don't usually have colours and patterns as attractive as these. They are really beautiful.

Alderman x Salmon Flowered F1
The F1 here is so unexpected in form I'm starting to worry that I might have mislabelled something. The flowers are a deep, dark, velvety purple with beautiful veining and are borne elegantly in pairs. It actually looks more like a Desiree hybrid than the product of its white single-flowered Alderman mother and pink cluster-flowered father. But at any rate it's been the least successful of the hybrids this season, because it hasn't set seed properly. The pods were late to form, and barely got past mangetout size, so there's virtually no viable seed for the next generation. I only found two part-filled pods of mature size, yielding a total of 3 seeds ... not a very helpful sample size for an F2 crop. Shame, as it has other useful traits as well as its flower beauty and paired pods. It's by far the most cold tolerant pea in the garden, still green and still flowering (albeit with straggly mildewed stems lower down) in late November after hard frosts, and even now still clinging on to life in January.

Mr Bethell's Purple Podded x Alderman F1
My original breeding project. This one is turning out pretty interesting so it'll be getting its own post very soon. The F1 plants produce dramatically bi-coloured green and purple pods with bold splodges (see photo above) along with pretty bi-colour flowers. Most of the F2 seeds it produced are purple-speckled, which is not uncommon for heritage peas but it's a trait not seen in either parent! But it really amazed me by producing one pod of F2 seeds which are actually purple. I've been aiming to breed for purple pods, but purple peas is something I've never seen before. See the pic at the top of this post. They are properly pigmented with beautiful purple right across their surface, it's not just a concentration of speckling. I really wasn't expecting that!

Alderman x (Mr Bethell's Purple Podded x Alderman)
This one is a backcross. In other words, I used an F1 hybrid to pollinate one of its own parent varieties. I know that sounds a bit incestuous, but it's actually a very effective way to transfer a dominant trait from one variety to another. In this case I'm looking to get the dominant purple-pod gene into a plant which otherwise looks and tastes like Alderman. This cross is a quarter Purple Podded and three-quarters Alderman, so I have a better chance of preserving the Alderman traits in its offspring while still getting some purple pods. In this instance however only one plant made it to maturity, so the seed sample is probably too small to make much progress with. I may have to grow more of this one to collect enough seed to take it any further.

Golden Sweet x Desiree F1
This is the hybrid I made on behalf of the Real Seed Catalogue, in the hope of developing a good purple-podded mangetout for them.

To all intents and purposes it looks like Golden Sweet but without the yellow. The flowers are attractive (bi-coloured) and borne mostly in pairs. Pods are predominantly purple, but with some green streaking. The F2 seed it produced was large in quantity but quite small in size, despite both parents having reasonably large seeds. This seems to be a common phenomenon with peas at the F2 stage.

Golden Sweet x Carruthers' Purple Podded F1
A companion to the Desiree cross above. And very similar to it in appearance, though perhaps slightly less vigorous.

Golden Sweet x Sugar Ann F1
You wouldn't believe that the father of this hybrid was a tiddly little dwarf variety of about one foot in height. The F1 grew very rapidly and voluptuously to over 7ft and was top heavy with its bounty. In appearance it was basically like Golden Sweet, but without the yellow. I'm not sure what the status of Sugar Ann is, whether it's protected by plant breeders' rights. Most of the crosses I make are based on heritage types which are in the public domain, but I suspect Sugar Ann is a modern variety. Anyway, it was super-vigorous and produced masses of F2 seed so I'm well set up to continue with it this coming season.

Other lines to look forward to (crosses already made and F1 seed ready to sow): Golden Sweet x Kent Blue, Ne Plus Ultra x Kent Blue, Magnum Bonum x Carruthers' Purple Podded, Mr Bethell's Purple Podded x Champion of England.

3 comments:

friary said...

Rebsie - I'm intrigued by the resulting purple peas as opposed to pods. Will be very interested when you get to tasting. I wonder if the exceptional sweetness of Alderman (that was my experience in 07) will come through?

Rebsie Fairholm said...

I certainly hope so! I'm still keeping my fingers crossed with this one because there's no guarantee that the colour will show up again in future generations, and I only have five seeds which are truly purple!

But it would be really good if I could keep it going because the purple pigment is anthocyanin, a wonderful antioxidant, so it would have health benefits as well as novelty value. And a bit of Alderman sweetness would be quite a bonus!

Matron said...

What a totally fascinating post! One of the most interesting I've read for ages. I am certainly a fan of saving my own seed each year, but lots of them do revert back eventually. Thanks!