Saturday 31 May 2008

Yellow Sugarsnap Project ... lots to report

Don't get too excited, this one looks very pretty but it's actually a yellow mangetout (snow) and only has one of the two recessive genes I'm looking for

There's been so much happening with the Yellow Sugarsnap Project, and so much else happening in the rest of my life, I haven't had a hope of blogging up all their progress. One issue is that I'm collecting huge amounts of data which I'm then having to type up and spend ages staring at, in addition to all the usual seasonal garden activity. So this is the best I can do for the moment. At least it'll give you a glimpse of what is happening with the project, which has reached its most exciting stage now.

A couple of years ago on this blog I claimed that naturally inbreeding plants such as peas don't show much hybrid vigour, if any. Well I'm having to eat humble pie now as my yellow sugarsnap F2 hybrids soar beyond a height of 7ft and show no interest in slowing down. They've massively outgrown the frame I made for them and are beyond the tops of the support sticks. This project is a cross between a 5ft variety and a tiny dwarf one which barely reaches 1ft in height, so I wasn't expecting anything quite like this. D'oh!

The original cross was Golden Sweet x Sugar Ann and this is the F2 generation.

Some things have turned out just as predicted ...

Flower colour is usually pretty simple in peas. Purple is dominant over white. So if you cross a white-flowered variety with a purple-flowered variety, the first season's progeny (F1 hybrid) should all have purple flowers ... and that's exactly what happened when I grew the F1 generation last year. In the F2 generation the genes are recombined, and approximately a quarter of them end up with the pair of recessive genes which enable white flowers to express themselves. So I expected to get purple flowers on three quarters of my plants and white on the others. And that's not far off what I've got. Hurrah!

I already showed you the first flower, which was purple (when I say purple, I mean the mauve and maroon bicolour which is common to many heritage varieties). The next four were all purple too, and then the next four were whites. A majority of the early flowers were white, but overall the ratio is 24 whites to 39 purples, which is not quite a Mendelian ratio but is not wildly far off it.

The joy of F2 variability. Sometimes they're white-flowered with a cream calyx and yellow stems ...

Sometimes they're purple-bicolour flowered with green calyx and stems ...

And sometimes it's the other way around.

Yellow pods are a recessive trait in peas, and again the inheritance is pretty simple because it's all down to a single gene. In a cross between a yellow-podded pea and a green-podded pea, all the first generation (F1) plants should be green-podded (and indeed they were). In this F2 generation the recessive yellow gene has a chance to assert itself and so roughly one in four plants should have yellow pods ... and so far that's pretty much what I've got. 19 yellows to 44 greens is as near as dammit the predicted Mendelian ratio.

It's quite odd to see these yellow and green pods all growing together, and to think that they're siblings from the same batch of seeds. Gene segregation in action!

Snap pods are another recessive class, so again I'm only expecting about one in four. In some cases it's still too early to tell which are sugarsnaps and which are mangetouts. Many of the mangetouts are obvious because the pods are already large and flat, but I haven't finished collecting data on this yet so there's no point drawing any conclusions. But at a glance I'd say the ratios are looking about right.

Tall plants outnumber dwarf plants considerably, which consist of 6 true dwarfs and 7 intermediate types (13 altogether). The expected ratio is three talls for every one short, because once again it's a trait which usually shows simple dominance.

Yellow tendrils grow alongside green tendrils, another variable trait in the F2 plants

Some new things I discovered, but they weren't huge surprises ...

There is a correlation between axillary pigmentation and purple flowers. All the plants with a deep pink splodge in the leaf nodes (whether it was a tiny smudge or a big blotch) went on to produce purple (bicolour) flowers, while all the plants with no trace of pigmentation went on to be white-flowered, no exceptions. Not entirely unexpected, although theoretically I can't see why these traits shouldn't be inherited independently because they're controlled by different genes. Maybe it's gene linkage, but I don't know to be honest. The genes controlling purple/pink colouring in peas are numerous and sometimes interrelate in funny ways.

A trait common to all purple bicolour pea flowers is that they turn a beautiful blue as they fade

There is a correlation between cream or yellow colouring on the plants and yellow pods, so all the plants showing any trace of yellow colour are turning out to be yellow-podded. No exceptions so far. The surest sign is when the first flower buds begin to form, because the buds have a very distinctive pale cream calyx (that's the leafy bit round the outside of the flower that looks like a pixie hat) which is easily recognisable even while they're still tiny. It's interesting that there appears to be just one gene controlling yellow colour, and it's an all-or-nothing kind of thing. Not like purple, which has separate genes (or even pairs of genes) for colouring different parts of the plant. It seems that if the yellow gene is there, you can expect to see yellow consistently in the stems, tendrils, calyx, pods and young leaves.

Pods per node is variable, as in many other pea varieties. Some bear their pods singly, some in pairs, and some show a mixture of both on the same plant.

And some things which were a pleasant surprise ...

New phenotypes are the most exciting aspect of breeding your own plants. Crossing any two varieties, especially those with a healthy bit of genetic diversity, is likely to throw up a few new traits not seen in either parent. It happens because genes interact with each other in a variety of ways and some can only express themselves when they hit just the right combination. While it's nice when all your predictions and ratios come out correct, it's not as exciting as seeing something totally wacky and unexpected show up in the F2.

So you can imagine how delighted I was to be presented with this:

New pink and white flower phenotype, which is essentially a white flower overlaid with pinky-mauve, giving a veined and mottled effect

This is the rear view ...

... and they age very gracefully too, producing more colours as they're going over.

Six plants out of the 63 are showing this new phenotype. What appears to be happening here is that the standard petal (the big one at the back) is white but the pinky-purple is trying to assert itself over the top. As the pink is stronger in the middle it gives this beautiful mottled two-tone effect. The same is true of the wing petal, where the maroon is spattered over a creamy white base. The overall effect is absolutely beautiful, and looks more like something you'd see in sweet peas than culinary ones. I really like this new type and would love to have a new variety like this, even though it's nothing to do with the original purpose of the project (distractions and sidelines are part of the fun).

The burning question is whether I can actually preserve this new phenotype in future generations and make a true-breeding stable variety out of it. The reason I'm uncertain is that I don't know what genetic factors are responsible for it. Maybe if I save seed from all the pink-and-white plants they will happily produce offspring with the same attribute, in which case I will be hopping up and down with joy. If, on the other hand, the unusual colour is created by co-dominance between two opposing colour genes then I'm stuffed ... because the genes will recombine and segregate out into pure white types and purple types. I would still get some of the pink-and-white types, but they would decrease with each generation and no amount of careful selection would be able to fix those colours.

There's more interesting stuff about these pink-and-whites. You may recall that when I sowed the seeds I separated them out into different seed types, according to their colour, wrinkliness and whether they had purple speckles. I did this so that I could look out for any correlation between seed type and plant traits. For the most part there hasn't been anything obvious, but ... four out of the six pink-and-whites are from Group 2, which was "smooth, green seeds with purple speckles". The other two are in a group which were selected for size rather than colour, so it's not possible to know what colour seed they came from, but they both came from the "small seeds with indeterminate markings" group.

And that's not all ... I'm intrigued to find that all six of the pink-and-whites have the sugarsnap pod type. Given that the sugar pod gene is recessive, it seems unlikely that it's simply down to chance. But I don't know what the explanation is. The most obvious is gene linkage. That's something which happens when genes are positioned close together on the same chromosome ... they tend to stick together rather than being inherited separately. The closer together the genes are on the chromosome, the less independent they tend to be. So it may be that one or more of the genes which make pink-and-white flowers (and of course I don't know anything about these genes yet) is on the same chromosome as the sugarsnap gene. And I have no complaints about that. I prefer sugarsnaps to mangetouts anyway, so if this is going to turn out to be a pink-and-white flowered sugarsnap by default, well, suits me.

There are other new phenotypes too, even if not quite so exciting. Here's another of the very pretty ones, a dwarf plant with exceptionally intense yellow colour. It's even got yellow leaf veins. The bicolour flowers have an unusual rolled tube shape. Pods are yellow mangetouts.

And the yellow sugarsnap itself? At the moment it looks like I have only one plant which is a true yellow sugarsnap (others may become apparent later, but I think that's the lot). This isn't entirely surprising ... there is only a one-in-four chance of a plant having yellow pods, and of those, only one in four are likely to have the recessive sugar-type pods. So overall that means a 1 in 16 chance of a yellow sugarsnap. Out of 63 plants I might have hoped to get more than one, but when you look at it from a statistical point of view it's not that wide of the mark. Better one than none at all!

The holy grail of this particular breeding project, a Yellow Sugarsnap.

For those who want to see the actual data I'm collecting on these plants I'm compiling them into a huge table and making it available online (on what will eventually be an extension-website to this blog but it's very much a work in progress). I'm still collecting data so the table isn't yet complete.

If you're inspired by what you've seen here but still thinking "what the heck is she talking about?" I heartily recommend a read of Carol Deppe's book, which is where I learned half of what I know (the other half coming from the garden itself). There would be no Daughter of the Soil without Carol Deppe!


Celia Hart said...

This morning I'm revising my main website - so I can totally appreciate all the hard work you must have put in to create your new web pages! What a fantastic resource!

I've been admiring the flowers on the pea varieties I'm growing this season, isn't it beautiful how they fade and turn shades of cyan and indigo. My favourites are the Victorian Purple Podded from this year's HSL selection, they are so elegant and have really strong wiry tendrils and leaf stalks (if you'd like seeds for next year let me know). I can't wait to see the Salmon Flowered ones from the seeds you sent - the plants are extraordinary!

Thank you for such detailed write-ups

Matron said...

That's just amazing Rebsie! I think I almost kept up with you for a while there! Thinking back to my schooldays I remember the lessons about Gregor Mendel and his peas! On a tangent note, I have a friend who is doing research into the dominant and reccessive traits of F1 hybrid (crossbreed) dogs!!!

GardenGirl said...

I am really enjoying your garden, virtually. It's always so exciting when I find you have posted again! I am growing sugar-snaps for the first time this year (a novice), from plugs... They are growing nicely, but are only about waist high and no-where near flowering... is this just because I am in N Yorkshire? I planted them early April.

I need orange said...

I love sugar snaps, and I love your pink flowers (and the purple flowers, too!).

It would be excellent if your pink peas follow on, and you become fabulously wealthy for your work on developing them!

Rebsie Fairholm said...

Hi Celia, yes I love the colour changes on purple pea flowers. Especially when there's lots of flowers at different stages so you get all the different colours at once. And yes please, the Victorian Purple Podded is one I don't yet have so I'd be grateful for some seeds next year. Glad the Salmon-Flowered is doing well ... it's truly unlike any pea I've ever seen.

Hi Matron - the yellow-podded Golden Sweet I used in my cross is allegedly one of the varieties Gregor Mendel studied. Cross-breeding dogs sounds fun, but probably takes up more space than peas...

Hi Gardengirl, thanks for your nice comments. I don't think you need worry about your sugarsnaps, they will probably flower in the next couple of weeks. I sowed mine in early March, which is why they've flowered earlier ... peas mature a certain number of weeks after sowing, regardless of what time of year you start them off. They are also a 'cool-season' crop so they should be very happy in N Yorkshire. The flower buds emerge from inside the folded up young leaves so you sometimes don't see them until they're almost ready to open and then whooosh, there's no stopping 'em.

I Need Orange - ah, I wish there was a way to make a fortune from the plants I'm developing ... but being a woolly-minded socialist I don't believe in plant patents so these will be 'public domain' varieties which people can share freely. My best hope is that someone will pay me for writing about it ...

Jeremy said...

What a wonderfully informative and entertaining post. You already know that I too love Carol Deppe's book. I just wonder; if publishing on the web (note, I say publishing, not writing) had been as easy 15 years ago as it is now, maybe I would have been encouraged to continue my own feeble activities. It is so nice to be able to share and receive support from a small, but growing, and widely scattered, but all-here-together community.

Rebsie Fairholm said...

You're absolutely right Jeremy, the support and encouragement I get from the online community is what keeps me going, and so you can be assured that I truly appreciate your comments. It's wonderful to be able to share the everyday triumphs, and the internet has a magical way of enabling like-minded people to gravitate together, wherever in the world they happen to be.

On a sidenote, I can only imagine how frustrating it must have been for Carol Deppe not to be able to include pictures in her book ... having worked in publishing I know how expensive colour printing is and how tight the budgets are for specialist books. With a blog I have the luxury of being able to show people exactly what I'm talking about.