Gene genie

Genes are the most wondrous things. What flower colour do you suppose I got when I crossed this white blossomed beauty ...




... with this gorgeousness of rosy-pink?




Well, I got this:



It's my F1 hybrid of Alderman x Salmon Flowered. It has just blossomed and produced flowers of the 'standard' mauve and maroon two-tone, the colour you get in field peas. Neither parent shows this colouring. Alderman is a delicious late Victorian pea with the snowiest of snow white blossoms. Its partner in this liaison was the strange umbellatum variety Salmon Flowered, supplied by the Heritage Seed Library, which is the only pea in my collection to have the particularly lovely two-tone pale pink and salmon pink flowers.

I don't know all that much about the genetics of pink flowers, but I know there are at least a couple of genes which can produce them. I don't know which one(s) are present in Salmon Flowered, but the ones I'm aware of are both recessive. The white flowers of Alderman are also recessive. (Yes, despite the fact that most garden peas have white flowers, it is a recessive trait.) When you cross two varieties which both have different recessive alleles controlling the same trait, some weirdness can show up in the hybrid.

So am I surprised that my hybrid came out purple? Actually, no, not really. I did wonder if it might. And here's what I think the explanation is.

I've mentioned many times in my pea genetics posts (for those who don't glaze over while reading them) the existence of a gene called A. That's short for anthocyanin. This particular gene is an on-off switch which controls the production of anthocyanin, the pigment responsible for all pink and purple colouration in peas. The function of A is that simple - on or off. There are other genes which control which part of the plant the colour is expressed in ... flowers, pods, leaf axils, seeds. They are all separate genes which can inherit independently. But none of them can express themselves without the dominant A allele which switches on the pigment production. Without it, the colour genes are still there but they are mute.

With Salmon Flowered, it's obvious that it has genes for colour in various places. The rosy pink blossoms, the pink blush on the pods, the soft pale pink smudge in the leaf axil. The presence of all these colours tells me that it has the dominant AA genotype - in other words, anthocyanin is switched on. Conversely, Alderman shows no anthocyanin pigment whatsoever. It is entirely green leaved and white flowered. I can safely assume that it carries the recessive aa genotype - in other words, anthocyanin is switched off.

Because Alderman is genetically incapable of producing anthocyanin pigment, I have no way of knowing what other colour genes it has hidden away, clawing at their nucleotides and begging for release. It's very possible that it has a full palette of colour genes, and that it wants to express purple flowers, splodgy leaf axils, purple stems, the works. Even though all these colour genes are dominant, they are helpless, disempowered, in the presence of aa. It's a curious subversion of the usual law of inheritance, with a recessive allele suppressing the expression of several dominant alleles.

Now this is turning into a very wordy explanation, but it's all so gloriously simple. The mystery purple flowers in my hybrid have almost certainly come from Alderman. I believe Alderman has the dominant gene which makes purple flowers, but it's not normally expressed in Alderman plants because they have no pigment capability. When I made the cross with Salmon Flowered, I gave it the 'on' switch. In a cross between a plant which is aa and one which is AA, the hybrid is going to be aA. The dominant allele gets the upper hand, anthocyanin is switched on, and all the colour genes in both varieties are free to express themselves. My hybrid is showing colour traits from Alderman as well as from Salmon Flowered.

I suspected this might be the case when I saw the colour blotches on the leaf axils in the hybrid plants. They were very prominent, with the dark pink colour streaking right out into the stems. Although Salmon Flowered does have pink in the leaf axils, it is very pale and subtle. This was quite different and could only really have got there if it came from Alderman. So I knew there was a good chance that Alderman might have a purple blossom gene as well, especially as those two colour genes are closely linked and usually appear together.

What this means for the F2 generation next year is that I will get a quarter of the plants unable to produce anthocyanin, and therefore having white flowers. Of the remainder, I will get mostly purples but I'm hoping that there will also be a few rosy pinks. I don't know exactly how the pink-flower gene works, so I wouldn't want to predict anything more than that at this stage.

Last time I wrote about my Alderman x Salmon Flowered F1 hybrid I said it was expressing the recessive trait for fasciation (stem widening). Well it isn't. It did show some fasciation, but it turned out to be from environmental causes and the plants reverted to a more normal pattern of growth. They do have very thick stems, but this is common to nearly all my F1 hybrid peas and I think it's mostly just hybrid vigour. They are, however, saving their flowers for the top of the plant, and have grown to almost 6ft before showing any buds. This, coupled with the late-maturing trait from Alderman, makes them very slow to reach maturity. That's probably something I will have to select against in the F2.

Meanwhile, jolly solstice blessings to all who observe such things.

Pea: Luna Trick

Last year's F2 plant which became the prototype for Luna Trick

I have at least three or four plant breeding projects which will be ready for naming in 2009.

This is the first ... a new mangetout (snow) pea called Luna Trick.

Named in honour of my friend and music collaborator Daniel Staniforth, a shining inspiration who plays cello for me along with a seemingly endless range of other instruments; Daniel releases his own alt-rock music under the name of Luna Trick, so this beautiful moon-like pea is for him.

Prototype, photographed 2008

Luna Trick was bred from a cross of Golden Sweet x Sugar Ann. It was one of the obvious stand-out phenotypes in the F2 generation in 2008, producing a beautiful and abundant plant, though its greatest asset is its outstanding flavour (which must be carefully selected for in future generations). This is what the variety should look like when it's stabilised:

Growing vigorously to 6ft, it has distinctive yellow-green stems, and bears single rounded moon-white flowers on pale yellow stems so curvy they sometimes turn right over and bloom upside-down. The calyx is cream when young but at maturity turns moon-white with green mottling. Pods are pale yellow, quite large and succulent. As they mature they take on a porcelain-like translucence and the small peas can be seen inside, 8 or 9 per pod. Being a mangetout type, Luna Trick is completely fibreless and the pods are edible at all stages. The absence of fibre helps give it its translucence but it also means that the pod cannot keep its flat shape at maturity ... the peas bulge through and the pod buckles and twists, taking on a crescent shape. The really special feature is the pod flavour, which is exquisitely sweet, and a major improvement on its yellow-podded parent. The flavour has a full and rounded character as well as being sweet, and the thickish pod walls are unusually juicy. Even at a large size they can be eaten straight off the plant with no trace of bitterness. The peas themselves are not huge but very abundant, and sweet enough to be worth eating in their own right, raising the possibility of this being a dual-purpose variety. The one fault the peas have is a tendency for the skins to split if watered too heavily or erratically (either by me or the English weather).

The absence of any fibre inside the pod makes it impossible for it to stay flat. It's a bit weird-looking, but I rather like it. The pods also turn porcelain-translucent as they mature, so you can see the peas inside.

Although this pea has got its name this year, that doesn't mean it's ready for general release ... it will probably need at least another year's work. The basic format of a breeding project goes like this: two varieties are crossed together to make an F1 hybrid. The F1 seeds are all mixed together and don't get a name or a number ... there's no point, as they all look pretty much the same. The only purpose of the F1 generation is to provide as much F2 seed as possible. The F2 generation is where the magic happens ... as all the genes in the lottery get re-shuffled randomly and create enormous differences between siblings. So I treat each F2 seed as a unique individual and give it its own identifying number. Once I've decided which of the resulting F2 phenotypes are worth pursuing, the number is then applied to all subsequent generations so I can keep track of its lineage. In this instance, the plant I wanted to keep was one called YSS 25 - quite simply plant number 25 in my Yellow Sugar Snap project (which so far has produced just about every imaginable phenotype except a yellow sugar snap, but never mind). So at the end of last season I collected all the seeds from YSS 25, and these are now F3 seeds. Although they will display a certain amount of variability they should mostly follow the blueprint set in the previous generation, so they don't get their own individual numbers ... they are collectively labelled YSS 25 F3, and are now the basis for a new variety. It needs to keep its number so I don't lose track of its pedigree, but you can see why I prefer to call it Luna Trick.

2009: new seedlings just starting to sprout. This is the F3 generation

It's still early days on this project, but I'm hopeful that Luna Trick will be among the first of the new pea varieties to be released. Why? Because most of its desirable traits are made by recessive genes. Recessives are the joy of a plant breeder's life because they are so easy to stabilise. For example, the yellow pods are made by a recessive gene called gp (golden pod). I can deduce that the Luna Trick prototype carried a perfect matched pair of gp genes ... because if it didn't it wouldn't be able to express yellow pods. If it had only one copy of gp it would default to green pods, with the yellows just showing up in a proportion of its offspring. The fact that it was yellow-podded means I can be fairly confident that all its offspring will be yellow-podded, because it has only gp genes to pass on. The same is true of many of its other traits ... it has matched pairs of recessive genes for fibreless pods (two genes), white flowers (one gene) and for sweet flavour (two or more genes), so I can expect it to have high levels of stability for all these traits. These characteristics are joyfully easy to predict.

Some of the variability is also predictable. Tallness is a dominant trait in peas, made by a gene called Le. The original Luna Trick plant was tall, but it was bred from a cross between a tall pea and a dwarf one so I don't yet know whether it has one copy of the Le gene or two. If it has inherited two, it will breed true for tallness. If it has only inherited one (which is statistically more likely) then I can expect to see the recessive dwarf gene show up in a quarter of the offspring, and I will have to keep selecting the tall ones for several generations until the dwarves stop showing up.

Fortunately with peas you can recognise tall and dwarf phenotypes very early on, while they're still young seedlings. This is because the difference between a tall pea and a short one is simply down to internode length ... the amount of stem it makes between each set of leaves ... which starts to show itself when the plants are only a few days old. Thus I should be able to "rogue out" any shorties before I even plant them in the garden. Though I will probably plant them separately from the others and keep some seed from them, just in case I ever want to create a short version of the variety. (My breeding work focuses on tall peas as they are wonderful and deserve a renaissance after being woefully neglected for the last 100 years, but some people do like dwarf peas so I'll keep the options open.)


You can also see from this picture that it has variability in the seed colour, and comes in cream or green. The colour of a pea seed is made by the cotyledons (seed leaves) hidden inside. The dominant cotyledon colour in peas is yellow/cream ... and clearly Luna Trick has inherited this ... but it has also inherited a recessive gene catchily called i, which produces green cotyledons. (Put into technical terms, it's heterozygous at the i locus.) I could select one colour or the other ... the green ones, being recessive, will breed true for greenness, while the dominant cream ones may be hiding recessives within them and will show some further variability. But I'm actually not fussed either way ... the seed colour is not especially relevant in this project, so I'm planting them all without selection. If I was a commercial plant breeder I would probably want to select more rigorously to get a uniform product ... but I'm not, so I'm more interested in maintaining a healthy bit of genetic diversity.

Having made all these predictions, "expect the unexpected" is the mantra of any gene-reshuffling endeavour. It's likely that I'll find some unforeseen variability in the twenty-five or so plants I'm growing in this generation. Some will be caused by hidden recessives making their presence felt, and some will be caused by pleiotropy (genes which have more than one function) and unexpected synergies between newly combined genes. But that's OK ... for me it's one of life's greatest joys to see these new plants emerge into the world, each one subtly unique, and see what gifts they have to offer.

More information about pea genetics can be found in the JIC Pisum Gene Database.

The joy of Mendelian segregation ... illustrated!

Nature makes order from randomness.

The photo above shows one of the pods from my Yellow Sugarsnap Project with peas segregating for seed colour. The pod is from one of my F2 hybrid plants (the second generation after the original cross) so the peas inside are F3. As immaculate as this alternating pattern is, it's entirely random.

I've just spent three days typing up descriptions of all my little packets of F3 seed from the Yellow Sugarsnap Project into a nice tidy table, and even as I handled each of my sixty-two seed packets (each plant's seeds carefully saved separately) and stared at them hour after hour I didn't notice the pattern. I noticed that some of the packets of seed are very uniform while others show a bit of variability. I thought that factor might be significant, so for each one I wrote down how variable the seeds were, and which traits they varied for. Sometimes it was size or colour, but more often it was a case of a few wrinkly seeds showing up in a batch of smooth ones. I dutifully jotted all this down but I still didn't notice the pattern. D'uh!

And then I was asked to do a little recorded talk about Mendel and his peas for a University of Bath podcast, just a very brief grounding in the history of genetics for psychology undergraduates. Not trusting myself to not screw it up, I did some refresher-research on Mendel. And in doing so I thought very hard about his experiments, and how he'd been the first person to notice the recurrence of 3:1 ratios in inherited traits. And it was only then that I twigged that there was a pattern in the seeds I'd collected from my pea project. So I raked them all out of the box and sorted them into different groups, and ker-ching! There it was. A beautiful and very obvious ratio.


As like as two peas in a pod? These F3 seeds from my Yellow Sugarsnap Project vary from smooth to wrinkled in the same pod, as well as varying for colour.

As a romantic idle speculation, I wonder whether Mendel found the same thing in his peas and got the initial idea for dominant/recessive segregation from it. Peas have this wonderful advantage over pretty much all other vegetables, that certain traits show up visibly in the seeds. If Mendel had been experimenting with tomatoes or brassicas this wouldn't happen because the seeds all look very similar no matter how different their genes are. He would have to actually grow the plants to see the differences between them. But with peas being the way they are, he must have seen a pattern very similar to what I have here.

The pattern is this: a number of my seed packets from the F2 plants have perfectly uniform round peas, with no wrinkles. A similar number have all wrinkled peas, with not a single round one among 'em. But a larger number have got variability for wrinkliness. And in every one of these cases they have, roughly speaking, a quarter wrinkled and three-quarters round. There are no other ratios. None of the packets have mostly wrinkled with just a few round, or even half and half. They all have an approximate 3:1 ratio in favour of round peas. A Mendelian ratio in other words. In fact there are two Mendelian ratios at the same time. The packets of round or predominantly round seed outnumber the packets of wrinkled seed by about 3:1, while the ratio of round to wrinkled within each of the variable seed packets is also 3:1.

I sorted the seed packets into types. On the left are all the seeds which are completely round with no wrinklies. On the right are the ones with all wrinklies and no roundies. In the middle are the packets which show a mixture of types. There are roughly twice as many in this middle group, as you can see.

Wrinkliness is one of the traits Mendel experimented with, and he found it to be recessive to roundness. This is now known as the R locus. The round-seeded allele is R and its wrinkle-seeded alternative is r. My original cross was between Golden Sweet (RR) and Sugar Ann (rr), so the resulting F1 hybrid must have had a genotype of Rr. Recombining those Rr genotypes in the F2 generation can go any of four ways, with visible effects in the seeds, like this:

Genotypes in the F2 plants can clearly be assigned to their four respective groups.

Why does seed wrinkliness matter? Well, it's a very useful trait for pea breeders to look out for because it's a rule-of-thumb indicator of sweetness. Sugars shrink more than starches do within pea seeds, so the sweeter ones tend to end up more wrinkly. A high sugar content doesn't guarantee a good flavour (as I found in my taste tests with these) but it helps.

It's obviously very useful to be able to identify the seeds which are likely to produce plants with sweet-tasting peas before you've sown them. If I want to breed a sweet-tasting variety I can just pick out and sow the wrinkly seeds and not the round ones, which will greatly increase my chance of getting what I want. This is a really unusual situation, and only works because the desirable trait shows up in the seed itself in an obvious way, when most other traits don't – you have to grow the plants to find out what their genetic make-up is, and even then you can't always tell. It's only because wrinkliness is recessive that I can be confident it will breed true.

Let me explain from a practical point of view. Dominant traits are a pain in the backside for plant breeders to work with. Say I wanted to breed a new pea with purple flowers, based on a cross between a purple-flowered and a white-flowered variety. Purple flowers show straightforward dominance in peas, so I would get ALL purples in the F1 generation followed by an F2 generation which was three-quarters purple and a quarter white. So I would obviously proceed by saving seed from all the purple-flowered F2s and removing the whites. When I sow the seeds from the purple-flowered plants, will they simply produce more purple-flowered plants? No, only a third of them will be true-breeding for purple. The rest will still have the recessive white-flower allele lurking in their DNA, hidden by its dominant purple twin. Although they look like true purples on the outside, those plants will again produce a 3:1 ratio of purples to whites. Unfortunately there's no way to tell which are true-breeding and which aren't, other than by growing them and removing all the whites in each generation until they eventually stop showing up.

Recessive traits, by contrast, are a joy. They show up in smaller proportions of course, but once you have a plant with the requisite pair of recessive alleles it should breed true from then on without any further mucking about.

That's why the sweet-wrinkly seeds showing up in a Mendelian ratio is such a godsend. Laying all these peas out on my desk in their individual packets, I can see their exact genotype for the R gene at a glance. The round seeded ones are RR and will breed true for roundness. The wrinkled ones are rr and will breed true for wrinkliness. The ones that are mostly round with a few wrinklies are Rr or rR (which amount to the same thing) and will continue to show variability in their offspring.

This is incredibly handy. Not only can I identify the sweet ones without having to grow them all and taste them, I can see which of them are true-breeding for sweetness/wrinkliness. If I want to be sure of getting a full complement of wrinkliness in my plants for ever after, I can instantly pick out the ones with the fully recessive genotype and Bob will be my uncle.

The reason this is possible is because this segregation for seed type is showing up within different peas on the same plant. Compare that to the situation with flowers. If some of the plants were obliging enough to produce a load of purple flowers and a smattering of whites all on the same plant, that would be great. I would know those were not true-breeding for purple. But they don't. They produce all purple flowers and keep the whites hidden in their genome to pass on to their offspring unseen.

OK, so we've established that the plants which produce only smooth, rounded seeds must be RR, and because they have a matching pair of alleles their offspring will also be RR. The technical name for this is homozygous. Exactly the same is true of the plants which produced only wrinkled seed. They are also homozygous, because their genotype must be rr and so all their offspring will be rr too.

The plants which produced a mixture of round and wrinkled types have to be heterozygous. Instead of a matched pair of alleles they have one of each type. That means that when they make seeds they will randomly pass on the four possible combinations to their offspring: RR or rr (which are both homozygous and will breed true) or Rr or rR (which are heterozygous and won't). The heterozygous seeds will express their dominant allele and hide their recessive one, so they will look the same as the RR seeds, and so once again there will appear to be a ratio of 3 rounded to 1 wrinkly.


Note that it's the plants which produced these seeds which are heterozygous, not the seeds themselves. Half the seeds in the heterozygous batch will actually be homozygous, but the other half remain heterozygous and will produce variable offspring which are half homozygous and half heterozygous, and so on ...
These seed packets are all siblings from the Yellow Sugarsnap project ... I still can't get over the amazing diversity made by this one simple cross!

With the two quarters of homozygous seeds separating out like this, you can see that in each generation half the heterozygosity is lost. If continued for a few generations it will all but disappear. That's how new varieties are stabilised.

In practical terms, what does that mean for these packets of variable seeds from the heterozygous F2 plants? Well, I know that I have all four classes mixed up here in approximately equal amounts, and I can see which seeds are homozygous (true-breeding) for wrinkliness, because they're wrinkled. Unfortunately I can't see which ones are homozygous for round seeds, because they look exactly the same as the heterozygous ones. Hence this 3:1 ratio of round to wrinkled. If I were to sow all these seeds, I would find the same 3:1 ratio in the next generation too, and onward.

Finally, a little reminder that all I'm looking at here is the R locus, the gene controlling wrinkliness. That's just one of many thousands of genes in every pea. Segregation is taking place at every other locus at the same time! If I select identical-looking wrinkled peas, I can assume they will be true-breeding for wrinkliness but they may differ enormously in other traits.

Wow, my head feels weird now.

The joy of genes ... illustrated!

Patient readers who have put up with me banging on about gene segregation and F2 hybrids ... here's a little photo sequence from one of my breeding projects to show the process in action. I hope this will be a lot more interesting and meaningful than my simply talking about it, since it shows what amazing and beautiful diversity is locked up within every seed. If it inspires you to have a go at some hybridisation yourself ... so much the better.

OK, so these are pictures of pea seeds from my Yellow Sugarsnap project. It matters not what the objective of the project is or how close I am to achieving it ... this is just an illustration of what happens when you cross two varieties.

In this case I started off with Golden Sweet, an old heirloom supplied by the Real Seed Catalogue, and Sugar Ann, a bog-standard commercial variety from a garden centre.

The original parent varieties. Golden Sweet (left) has dimpled tan or grey seeds with purple speckles, while Sugar Ann has pale grey-green or cream seeds which are more wrinkled and slightly bullet-shaped.

So I made a cross between these two varieties, thus creating an F1 hybrid, and this is what the seeds looked like:

F1 hybrid between Golden Sweet and Sugar Ann

Sorry this is a bit of a small sample, but I'd already planted most of my F1 seeds by the time I took the photo. Anyway, you may notice that the F1 hybrid seed looks exactly the same as the original Golden Sweet seed. There's a good reason for that. The embryo hidden deep within the seed has the hybrid DNA made by the cross-pollination, but the rest of the seed (including its outward shape and colour) is the product of the mother plant. Therefore it looks just like any other seed produced by the mother plant. If I'd done the cross the other way and used Sugar Ann as the mother plant, then all the F1 seeds would have looked like Sugar Ann.

The next step was to grow the F1 seeds and collect seed from them, giving me the F2 generation. I didn't make any further crosses ... as peas are self-pollinating, all I had to do to obtain the F2 seed was to grow the F1 plants and allow them to produce seed naturally. This is the result:

F2 hybrid between Golden Sweet and Sugar Ann (i.e. the seeds from the F1 plants)

Hey up, now we've got something happening. The F2 seeds no longer look exactly like the Golden Sweet parent. In fact if you look closely they're all different. The differences are quite subtle but they vary in colour, size and shape. Some are wrinkly while others are smooth or dimpled. Some have purple speckles, others are plain. They show a jumbled up mixture of traits from the original parent varieties, caused by the random segregation of genes from both parents.

This is the point where plant breeding becomes immensely fun. Because every one of these F2 seeds produces a plant that is unique. And once again I don't need to do any crosses, I just grow the F2 plants and let them set seed naturally to produce the F3 seeds. And I get THIS:

F3 hybrid between Golden Sweet and Sugar Ann (i.e. the seeds from the F2 plants)

This is actually just a random sample, the first nine plants to reach maturity. There were many many more variations, but these few are enough to show you what's happening. I've saved seed from each F2 plant individually, and you can see that there is some consistency in the seed type for each plant, but HUGE variability between plants. Plant 58 produced seeds the same shape as Sugar Ann but a much brighter green and with purple speckles. Plant 02 produced seeds the same shape as Golden Sweet but green instead of tan. Plant 25 produced exceptionally wrinkled seed with no speckles. Plant 09 produced large round smooth yellow seeds which are totally unlike either of the original parents. Plant 14 shows some variability within itself but again a spectacular diversion from the original parent varieties, because the whole seed coat is sploshed with solid purple with a few bright greens and pinks thrown in.

Same image, detail

Every one of these packets of F3 seed is a brand new, unique variety in its own right. I could give them all names and launch them on the world. There wouldn't be much point doing so, partly because their offspring would still show some variability and further segregation (so they need to be stabilised for a few more generations first) but also because they won't all be worth pursuing. At a glance I'd say that Plant 09 with its big smooth yellow seeds is probably not going to taste good. In fact I did eat some of its seeds while they were still fresh and they were hard, mealy and bitter. By contrast, the exceptionally wrinkled seeds of Plant 25 indicate an exceptional sweetness, confirmed by taste tests, and that one is probably worth pursuing. Plant 37 also looks useful, as it has the supersweet ultra-wrinkled seed combined with pretty purple, pink and green colouring. There's enough interesting material here to keep me occupied for years. All from a single cross!

Anyway, what I hope this illustrates is that all these seeds are different from the original parent varieties in ways I couldn't have imagined when I made the cross. There are some familiar traits showing up, but also a lot of brand new ones which weren't displayed by either parent. And some of those brand new traits are really quite exciting.

What these pictures show is segregation for seed-coat colour and seed shape. Because in peas those two traits are readily observable. Of course the same level of segregation is happening to ALL traits right across the genome, with potentially millions of different combinations. I hope this gives some idea of how much diversity and scope for new varieties is possible just from making one simple cross-pollination.

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!

Pea update: yellow sugarsnaps

Jeremy said the eyes of the world would be on my yellow sugarsnap seedlings. Well, here they are Jeremy, I hope you like them (and the rest of the world does too).

The F2 plants are all slightly different but the differences are subtle at the moment. Purple leaf axil splodges are now showing up on a lot of plants as expected, although it's been slow to develop. The splodges indicate the genotype A_D_ and its assorted variants. A is the gene for anthocyanin production and D is the gene for the purple splodge. They are both dominant. The size, shape and intensity of the splodge varies from plant to plant though, so there are probably other genes at work too. Some plants have a cream band inside the purple one, some don't, others just have a faint trace of it.

This one (below) has no purple splodge in the leaf axil and no other purple or red marking so is presumably the recessive genotype aa. Whether it has D_ or dd I've no idea because D can't express itself in the absence of A. Ah, the joy of genes!


Another thing I've noticed. The dwarf plants have darker, grey-green leaves compared to most (though not all) of the tall plants, which are more yellowy-green. I have no idea yet whether this is genetic or caused by something in the environment, or an interaction of the two. The F2s have separated into dwarf and tall types in a beautiful Mendelian ratio despite the small sample size, and I planted all the dwarfs along the front edge of the frame so they don't get swamped. It may be that they're getting more sunlight, or it may be that their short stature concentrates the chlorophyll in a smaller area and makes them go darker.

If it is genetic, why would there be a correlation between short height and darker leaf colour? One possible explanation is gene linkage. Genes are arranged in long sequences on chromosomes, which break up and rearrange whenever a seed is produced, to form a new genome for that individual seed. Peas have seven chromosomes. If the gene for dwarf height is on one chromosome and the gene for darker leaves is on another, those genes will be independent of each other and will usually recombine freely in the offspring. But if the two genes are close together on the same chromosome, it's much less likely that they can be inherited separately. The closer they are, the more they will stick together. In addition to this, it's very common for genes to interact with each other and even for a single gene to have more than one function (pleiotropy is the technical name for it). Any of these factors could be involved.

Another possible explanation, of course, is coincidence. Just because all my dwarf peas have darker leaves, it doesn't necessarily mean there's a reason for it. As I said, it's a small sample size and I can't draw too many conclusions from it at this stage.


Almost all the F2 plants have got serrated leaf edges, but again there's variability in how strong it is. Some have subtle little points and spikes along the leaf margins while others are boldly zigzagged and look like someone's cut round them with pinking shears. One of the parent varieties, Sugar Ann, has boldly serrated leaf margins while the other, Golden Sweet, shows some variability. Most Golden Sweet plants have smoothly rounded leaf margins but serration does sometimes show up too. I assume there's a dominant gene involved here, which is either not fully penetrant in Golden Sweet or is interacting with other genes. My other breeding project involving Golden Sweet hybrids is showing the same thing, a strong dominance of serrated edges.

Everything I've written here is just idle speculation, I must emphasise. I no more understand the genetic make-up of these plants than I know what colour knickers the Queen is wearing. It's all down to observation and guesswork. I will probably have to grow another couple of generations of plants before I can draw any firm conclusions.

The Real Seeds Purple Mangetout Pea Project

Photographed in 2007, this is a home-made F1 hybrid, Golden Sweet x Carruthers' Purple Podded

I've talked a bit about my yellow sugarsnaps and I'll post another update on those soon. But it's about time I posted about my Purple Mangetout project again.

To briefly recap, Ben of The Real Seed Catalogue asked me to produce a new pea variety for him because he wants to be able to offer a good purple mangetout pea and currently there aren't any. You can eat purple podded peas at the mangetout stage, but they don't have anything like the sweet and crunchy pleasure of a green-podded mangetout. There's no particular reason for that, except that nobody in the crop development industry has bothered to breed a mangetout with purple pods because pod colour has no agricultural importance ... so the job falls to amateurs like me.

Ben's favourite mangetout pea is Golden Sweet, which is a yellow-podded heirloom pea with red-flushed stems and purple flowers. It's a spectacularly gorgeous variety (see my pictures), it's tall and voluptuous, and the bright yellow pods are sweet and crunchy and delicious. There's nothing else remotely like it. He considers it the best mangetout there is, so basically what he wants is a pea which is just like Golden Sweet but with purple pods instead of yellow ones.

In theory that should be quite easy to achieve. Golden Sweet already has many of the genes associated with purple-podded peas. Most importantly, it has the gene which switches on the production of anthocyanin (purple pigment). A whole load of other genes are involved in determining which parts of the plant the anthocyanin shows up in. To turn Golden Sweet into a purple-podder, all I have to do is get hold of the genes which make purple pods and breed them into it. Purple pods in peas are controlled by two dominant genes, which I can get from any purple podded variety. And I can transfer those two genes into Golden Sweet by a method known as recurrent backcrossing.

It works like this. A cross between Golden Sweet and a purple-podder is going to have half its genome from each parent. The offspring at the F2 stage will have a mixture of traits from both parents, all jumbled up. Let's say I select one of the F2 plants which has purple pods, and cross it with Golden Sweet. This is known as a backcross, because I'm crossing it back to one of the original parent varieties. The resulting offspring (F3 generation) will have three-quarters of its genes from Golden Sweet and only a quarter from the purple podded variety. Hopefully there will still be some offspring with purple pods though. So I select those again, and backcross them with Golden Sweet again ... giving me an F4 generation which is seven-eighths Golden Sweet and one-eighth the purple. By using this method up to the F5 generation, I should end up with a fairly true-breeding variety which is almost entirely Golden Sweet but with purple pods! Recurrent backcrossing is a powerful technique because it eliminates a lot of unwanted variability very quickly while enabling me to hang on to those two dominant genes which make purple pods.

That's the theory anyway!

If all goes according to plan I should have a stable new variety by the end of 2009.

Another photo from 2007. This time it's the Golden Sweet x Desiree F1 hybrid

So how's it panning out in practice? Well, I grew the F1 plants in 2007 and you can see from the pictures how they turned out ... they were pretty much as expected. When I crossed Golden Sweet with a purple podded pea, the offspring (F1 generation) all had purple pods. That's because the purple-pod genes are dominant, and they mask out Golden Sweet's recessive yellow-pod gene completely. In fact there was no trace of yellow colouring anywhere in the plants. As for the pods, they were all purple as expected, but partially blotched with green. I've been getting this in all my purple pea hybrids. When I cross a purple-pod with a green-pod, I get a marbled swirl of purple and green in the F1. When I cross a purple-pod with a yellow-pod as I did here, I still get a marbled swirl of purple and green. There are two likely causes I can think of. One is co-dominance, where the dominant purple genes fight with dominant green genes, and you end up with a mix of the two (if so, I should see them separate out into solid colours again in the F2 generation, about half and half of each). The other possible explanation is incomplete penetrance, where the purple-pod gene simply doesn't assert itself fully, for reasons best known to itself. I think on balance this is the most likely cause. The pods in the picture (Golden Sweet x Desiree) are the ones showing the most solid purple ... most of them were decidedly blotchy.

I'm working with two separate crosses in this project. Ben sent me a purple-podded pea called Desiree to do the cross with. It's not a variety Real Seeds currently sell, and I don't know much about its origins. It's a semi-dwarf variety (an unusual thing in peas) which grows to about three feet high. It's bushy and has beautiful flowers borne in pairs. The pods are just beautiful ... a rich dark indigo-purple colour, wide and flat, and ripening into fat little leathery pods with a glowing burgundy colour. It's normally grown as a soup pea and when the pods are mature they're so tough it's a job to pull them off the plant. My own favourite purple-podded pea though is Carruthers' Purple Podded, which is very different. I trialled a number of purple podded peas last year and there was a lot of difference between varieties. Carruthers is tall and refined with elegant, lantern-like flowers borne singly on long curvy stems. It has a brighter burgundy pod colour than Desiree, and smoother, sweeter-tasting pods. So I decided to make two separate breeding lines for this project, Golden Sweet x Desiree and Golden Sweet x Carruthers' Purple Podded, and to grow them side by side and see what differences there are.


The F2 seedlings, photographed a week or so ago. Golden Sweet x Carruthers' Purple Podded in the top picture, Golden Sweet x Desiree below.

I saved seeds from the F1 plants of both crosses. And a few weeks ago I sowed them, three each in bog-roll tubes. These are the F2 generation, and this is where the interesting stuff starts happening. The plants in this generation should segregate into roughly a quarter yellow-podded and three-quarters purple-podded, but I'll have to wait and see. I sowed 27 seeds of each cross, but germination has been quite erratic and I currently have 18 seedlings of GS x D and 19 of GS x CPP. I may sow a few more, but in theory I shouldn't need too many. As I'm looking for traits associated with dominant genes, I expect about 3/4 of these plants to have what I want. Very different from the Yellow Sugarsnap Project, where I'm after two recessive genes and will only get them in about 1/16.

This is the sort of splodge I'm getting in the F2 leaf axils. Seen here on a GS x CPP seedling.

The F2 seedlings are still small at the moment, but there are already some obvious differences. The GS x D cross is segregating into 3/4 tall and 1/4 short (which is normal in crosses between tall and dwarf peas) while the GS x CPP seedlings are all of a similar height because they are a cross between two tall varieties. Almost all the seedlings have purple splodges in the leaf axils, but they vary as to how much they have and how splodgy it is.

Purple spots on GS x D

And now here's a curiosity. About a quarter of the plants in both crosses have purple spots on the leaves, which is not something I've seen in any of the parents. I assume there's some recessive trait in Golden Sweet coming through here.

What larks.

On F2 seedlings and other stuff

Photographed on Saturday, just 9 days after sowing. Golden Sweet x Sugar Ann F2 seedlings.

I'm still struggling to keep up with everything (music is going well - four lots of radio airplay this week!) but I wanted to show you how well my F2 seedlings are coming along.

There's lots more going on. I'm hoping to get a greenhouse (what a dream come true that would be!) if I can find someone to put the bloody thing up as I don't fancy wielding large panels of glass above head-height myself. Meanwhile my home-made coldframe collapsed in a storm a couple of nights ago and splatted my crimson-flowered broad beans, which is not surprising given that the frame wasn't actually held together with anything except gravity, flowerpots and force of will. I think the beans are salvagable. And my next door neighbour kindly helped me cement-in a new post at a sensible height for the washing line which runs along one side of the garden, so I no longer have to garotte myself each time I go in and out of the vegetable patch.

I've been caught off guard somewhat by the way my Yellow Sugarsnap F2s have sprung into action. They are actually getting to the size where they'll need to be planted out soon, and I was banking on them taking a little longer so I could leave it till the weather is more reliable. It was also a little unfortunate that having had the sunniest February on record they happened to germinate just as we went into a few days of grey murky weather so when I photographed them on Saturday they were looking a bit leggy. But a few days of sunshine since then have fattened them up nicely. Here's what they look like today:


Something I didn't mention in my previous post on the Yellow Sugarsnaps is that I'm also growing small amounts of each of the original varieties, Golden Sweet and Sugar Ann. It's very useful in any breeding project to have the parent varieties as a control group. No matter how well you think you know a variety, there are bound to be some traits showing up in the F2 generation which make you think "which parent did that come from, or is it something completely new?" It's also useful to have plants of the parent varieties flowering at the same time in case I want to do a backcross. Backcrossing involves making a cross between an F2 plant and one of the original parent lines. It's a very useful technique for stablising a potential new variety, and for making the offspring more like one parent than the other. Having said that, it's unlikely that I will want to do any backcrossing with the Yellow Sugarsnaps because the class I'm looking for is a double recessive with one recessive trait coming from each parent. If I backcrossed to Golden Sweet I would probably lose the plump sugarsnap pods and if I backcrossed to Sugar Ann I'd lose the yellow colour. To retain those two recessives I will probably have to keep inbreeding from the F2 and select out any unwanted variability in future generations. That's the plan. But ... it's still worth having the parent varieties on hand, just in case.

It's a lot of fun looking at the F2 seedlings and trying to spot the differences. One difference is immediately obvious. Most of the seedlings are tall and lanky but some are short and chunky instead. There are 12 shorties among my tray of 64 plants ... now that's looking like a Mendelian ratio! And it's one I was expecting, because it's actually the first one Mendel himself spotted. I'm really following in Mendel's footsteps here because Golden Sweet or something incredibly like it was one of the varieties he experimented with and led to him discovering the existence of the ratios which are named after him. In peas, the tall gene is dominant over the short gene, so when you cross a tall pea with a short pea you get a ratio of 3/4 tall to 1/4 short in the F2 generation. My project is a tall x short cross, so in my batch of 64 plants I would expect about sixteen to be short. Twelve is near enough. To be honest 64 plants is quite a small sample size so I'm unlikely to get exact ratios. When Mendel did this he was working with hundreds of plants at a time, so the ratios stood out more clearly.

Not easy to photograph a Mendelian ratio, but you get the idea. You may notice one shortie which is a lot redder than the others ... they're all different.

I also mentioned before that sometimes it's the lack of a Mendelian ratio that makes things interesting. One that's surprising me is a complete lack of purple splodges in the leaf axils. I was expecting to see it in around three quarters of them since it's controlled by dominant genes, but none of them are showing it. I have no explanation for that at the moment.

Of course, the Yellow Sugarsnap project is just one of several pea breeding projects I have on the go, and when I get a moment (aaaargh!) I will show you some pictures of the F2 seedlings I'm growing for the Real Seeds Purple Mangetout Project.

Yellow sugarsnap project: sowing the F2

A few days ago I sowed the first batch of F2 seeds for my yellow sugarsnap pea experiment.

I love the variability of F2 pea seeds. Most plants produce seed which looks pretty much the same regardless, so you don't get any clues as to what you're going to get from a breeding project until you actually grow the plants. Peas are unusual in that the seeds do have tantalising variations and elusive hints of what they might develop into. But you don't get to see it until the F2 stage.

When you cross two pea varieties, the resulting F1 hybrid seed looks just the same as any normal seed of the mother variety. That's because the seed is a product of the mother plant. The father's DNA is in the seed embryo, but not in the outer structure of the seed. Only occasionally will an attribute from the father be visible in the seed itself. But when the F1s are grown and self-pollinated they produce F2 seed which is very diverse in appearance. A large green crinkled pea may easily be sitting side by side with a small round tan-coloured one, right there in the same pod. The phrase "as like as two peas in a pod" is thrown out the window.

Segregating the F2 seeds into different groups

My F2 seeds show a mixture of characteristics from both breeding lines. They have some of the grey and tan colours of Golden Sweet, and varying degrees of purple speckling. Sometimes the speckles are clear and dense, other times they're blurred like purple ink on wet blotting paper. Some have the green colouring of Sugar Ann (with or without speckles) and its surface wrinkliness, while others are smooth and dimpled.

I had a slight dilemma about whether or not to segregate the seeds and plant them in groups of different types. I thought it would be interesting to see if there was any obvious correlation between the outer appearance of the seed and the type of plant that results. Some traits are known to show up in pea seeds. Wrinkled peas are an indication of higher levels of sweetness, because sugar within the seed shrinks more than starch does. It's not a hard and fast rule though, because peas often go more wrinkly if they were dried rapidly after harvest. The presence of purple speckles may indicate that a seed contains the gene for anthocyanin production (the substance which makes purple colours) which is present in Golden Sweet but probably not in Sugar Ann. I think it less likely that the actual seed colour will have a correlation with any obvious trait, but it might do. However, I had to think carefully about whether I wanted to plant them in separate "types" or not. Any selection or grading I do at this stage, however well-intentioned, risks screwing up my Mendelian ratios. And I'm relying on the ratios to give me information about the genetic makeup of the material I'm working with, which is how I decide how to proceed with it at the next stage. By looking at the Mendelian ratios (or lack of them) I will be able to work out which traits are dominant, which are recessive and which involve co-dominance between two opposing genes, and various other patterns.

In the end I decided the observations about seed type were important, or at least that it would be a shame not to try it and see, so I separated them roughly into eight different groups, one for each row of modules. It was entirely subjective, separating them into types when really they're all different. As I sorted through them they were all shouting "me me me!" But this is what I ended up with.

Row 1 - smooth, green, unspeckled
Row 2 - smooth, green, speckled
Row 3 - smooth, tan, speckled
Row 4 - wrinkled, unspeckled (of any colour)
Row 5 - wrinkled, tan, speckled
Row 6 - wrinkled, green, speckled
Row 7 - large, with indeterminate markings
Row 8 - smaller, with indeterminate markings

As I explained in a recent post, I'm looking for two recessive genes in this project, one for yellow pods and one for chunky sugarsnap-type pods, and my chances of getting both traits in a single plant are one in sixteen. Statistics are all very well, but the trouble is I can't just plant sixteen peas and be sure of getting one yellow sugarsnap. It doesn't work like that. So how do I know how many to plant? More statistics! I look it up in a chart in the back of Carol Deppe's book. According to that, if I want to be 95% certain of getting at least one yellow sugarsnap (where the chances are one-in-sixteen) I need to grow 46 plants. If I want to be 99% certain, I need 71 plants. My husband tells me the 95% threshold is perfectly adequate, but I have room for 64 plants in my root-trainer modules, so that's what I went with. It's useful being married to an academic scientist who can help me think out my experimental methods, but if I wasn't I would probably just sow the bloody lot and not worry about it.

I sowed the seeds last Thursday, and they germinated really quickly. The first seedling popped its head up less than 4 days after sowing, and by this morning (5 days) there were 30 seedlings visible, which is almost half of them. One thing I can say at this stage is that there's no correlation between seed type and speed of germination ... they're popping up equally happily in all the different groups.

Photographed this morning, the emerging seedlings