28 November 2011

Just went and checked the green seed from drying pods off my Melting Mammoth that I sowed a few days ago - one of the peas has already sprouted! Most pleased - I have just picked the fully developed pods from my first crosses in the first few days of November, so am thinking of sowing some tomorrow or in a couple of days. Have put the pods in the dehydrator this morning - on very low -  to hasten the process, but I'm not sure that I should have...
If I sow tomorrow or the next day, I should have emerging plants before I go away 2nd week of December, then leave them on the watering system in big pots to grow until I get back. Cut a few weeks out of the cycle.

I've spent the weekend musing on strategies now that I've actually got some material to work on.

Of my early crosses I got full pods from the first 5 crosses or so (the later pods are very incompletely filled, so that material will probably have to wait until late summer for sowing - I can't afford to take risks with it). These were hangover crosses - being a bit under the weather, I used recessive pollen on dominant mothers, so I won't be able to tell from the F1 plants whether my crosses were successful or if the seeds are from self pollinations. I also wrote down the names wrong citing Oregon Snap as the pollen donor - except there is no Oregon Snap parent - and a few days later when I re-read the labels, I couldn't remember whether I had used Sugar Snap Bush or Oregon Spring pollen. At least they are both white flowered,multi flowered, powdery resistant, dwarf, edible podded - just that Sugar Snap Bush also carries the n gene for thick pods.

I've got 3 full pods of these mislabelled crosses, so i could potentially have 18 or so seeds. I can probably afford to experiment with half, say 9 seeds.

However, the Lost Seed Co variety of purple podded (PP(LSC)) only developed 4 full pods on each plant. At say 6 peas per pod, that's only 24 F2 seeds per F1 plant - not a lot for a grow out. But I could get ~ 500 seeds at the F3, enough for a substantial grow out of say half, with half put aside to delve into if nothing turns up in the first F3 batch. So this week I might sow half the seed from these first crosses (which were 'wrong way' crosses), 12 weeks to seed harvest (that's what the first generation took) takes me through to the end of February, sow all the F2s to have them flowering at the end of April, with seed for sowing at the start of May. If I get about 12 seeds from each of these summer grown peas (Rebsie suggests seed number and quality is poor from hot weather plants), I could potentially have ~100 F2 seeds for late February sowing.

The F2s will have segregated and various traits will have been expressed, so I might have some stable recessive lines - dwarfism or powdery resistance or uncoloured leaf axils to select from. I'm not going to be able to tell about the low fibre pod characteristics without sacrificing some pods, which I'm not willing to do. Since I'm after purple podded snows, I would put the seed from the uncoloured leaf axil plants to one side, and grow out the rest (depending on number) - purple axil colouration seems to be linked tightly with A the anthocyanin gene which I need for purple pods - at least according to Mendel. Since it is dominant, if the plants were carrying even one copy (heterozygous) it would be expressed, so no purple axil, no A.

I've also crossed Purple Podded (Select Organics) with Yellow Podded, looking for a red pod. For a red podded I need purple pods (A_Pu_Pur_) over yellow pods gpgp. Yellow Podded already carries A, so all the progeny of the crosses will be AA. So to get a red podded in the F2 generation I need Pu_Pur_gpgp, the odds of which are 3/4 X 3/4 X 1/4 = 9/64 or about 1 in 7 - if the genes are independent.

So I might also sow some of the PP(SO)XGP F1s this week - since the outcome is not really a huge target for my program, the seed is a bit expendable, and it might be encouraging to see how it segregates next autumn. And I might just turn up something interesting...

Ditto with my Yellow Snow crosses, trying to turn up a half decent yellow snow pea. I've crossed Golden Podded with Oregon Spring and Delta Louisa, both dwarf double flowered snows. I should have a few seeds to spare, so I might try a few out.
(I'll come back and put some pics in this post a bit later)

26 November 2011

Cross pollination aid for middle-aged eyesight

I've been wandering out early mornings with my first cup of coffee for the last month or so, seeking flower buds for crossing purposes. But in the dim 6 am light, a certain wine induced bleariness, and my aging eyes, emasculating tiny buds - which have been getting tinier as the season warms up - has necessitated some visual augmentation.
I could have purchased some neat fold down magnifiers, but they are a bit steep in price, and I procrastinated, and didn't order them, two weeks delivery for online purchases, blah blah blah, so this morning, frustrated, I dug out a couple of hand lenses, an old peaked cap, and tried to get a self supporting magnifier that left both hands free for delicate surgery.

Wasn't working...then i remembered my old bike helmet, which I had rigged up with an eye level rear vision mirror - before these things became standard attachments in the eighties - which dates me and the helmet. A bit of foam from a shrink wrap vege tray to protect the mirror, a bulldog clip, and I'm set...

25 November 2011

Aberrant Angela's Blue - musings on heterozygosity

I'm growing four or five plants of each of my purple podded parent lines, one of which is Angela's Blue. However, one of the plants seems to not be carrying its full complement of purple podded genes. As discussed elsewhere, I need A to turn on anthocyanin production, and Pu and Pur to express this colour in the pods. I've been wondering what would happen if I only got one of Pu or Pur as a result of one of my crosses. This aberrant plant of Angela's might indicate the result. It shows a dappled purple colouration.

A developing pod on Aberrant Angela's Blue
The plant has only two pods, so it might not be a good plant to choose as a pollen donor, but both pods show this patterning. So how might this have arisen?
A, Pu and Pur, the three genes needed for purple podding are dominant. Whoever bred Angela's would have had to select for purple podded phenotype from their original cross. This means the plants they selected from would have had to be carrying A, Pu and Pur. But you can't tell if the plant has one copy of the dominant gene (heterozygous) or double copies (homozygous) unless you grow out lots of the progeny. My guess is the original parent was heterzygous, was grown out for a number of generations until the breeder thought it was homozygous for all three genes, but lurking in the population from which the seed was collected was a plant which was heterozygous for either Pu or Pur.

This is what a purple podded is supossed to look like:

18 November 2011

More genes: flower number

Peas that carry multiple pods per node are considered more desirable - although some reports suggest that rather than increasing yield, it may reduce it - the plant puts extra resources into flower and pod production, depleting the overall performance of the plant. I haven't done any tests, but I like the idea of compact plants producing lots of pods, so I'm thinking of trying for pultiple flowers.
This is controlled by two recessive genes, fn, and fna.

They are interactive -fn or fna alone gives two flowers, fn fna together gives two or more flowers. However, the genes may be incompletely expressed; flower number is also influenced by environmental conditions.

#1836, a tall multiflowered pea from Greece, showing repeated double flowering nodes
Some of my multi-flower lines alternate single flowered nodes with double flowered nodes - Melting Mammoth for example. But some of my Jovian accessions, Salahi, a white flowered semi dwarf fibrepodded pea from Nepal, or #1836 a purple flowered from Greece, for example has almost all double flowers - perhaps there is some gene interaction going on, that partially overrides the environmental limitations on the other varieties.

It would be nice to get both fn and fna - I will probably need to cross a number of multiflowered lines to see if I have both genes...

14 November 2011

Some genes of note 2: stem length.

 Personally, I prefer medium height veges - I'm a bit over all the staking and tying up required for monster vegetables - towering 9 foot tomatoes and beans that are out of reach all require extra work in the garden - I prefer a neat plant head high or less. Where folks are limited for space I can see the point, or for boasting rights, but the structure needed to hold up a huge fully loaded tomato plant for example is considerable. While I am a bit limited for space, the defining limitation in my central Victorian garden is water, followed by nutrients, then sunlight. If I want to optimise variety, then smaller plants with modest requirements are what I need. Less energy put into construction means more time and energy for other stuff. So I would like to breed dwarfism into my peas.
My go-to genetic resource, the JI database has some interesting info on stem length in peas.

 Genes coh, cona, and cot all shorten internodes. The database is silent on how these interact.
Long internodes
le shortens internodes and gives a zigzag stem pattern
lh gives a 60-70% reduction in internode length
lka gives reduced internodes and "reduced branching and peduncle length, stem banding"
lkb and lkc also reduce internode length, with other physiological changes.
lm reduces internodes but effects  roots.
lw gives "reduced internode length by 50%. Delayed flowering especially under short days"
na is "compact dwarf with extremely shortened internodes"
Short internodes on Delta Louisa - perhaps a hint of zig zag?

So, I wonder which of these genes is regulating internode length in Delta Louisa, Oreson Spring, Sugar Snap Bush, and Sahali, all of which exhibit short or shortish stems...

Some other genes of note: disease resistance

In addition to the genes for colour, some of which I've discussed in a previous post, there are a number of genes of home horticultural importance.
Foremost are probably the genes for powdery mildew resistance. There are two genes, both of which confer resistance to Erysiphe polygoni the organism responsible for powdery.
They are known as er-1 and er-2, both are recessive. The JI database notes of er-2 "Resistance broken under controlled growth conditions so not as durable as resistance conferred by er-1".
Being recessives sahould make them easy to fix, but since the only phenotypic expression is disease resistance, it is hard to distinguish whether they are present or not until E.polygoni strikes, and then how might one distinguish between them?

I have at least one line that has at least one of these genes - Delta Louisa is powdery resistant. And by the looks of my recent observations it appears that Oregon Spring, another dwarf snow pea line is also resistant. On the left of the photo is three purple podded lines - PP Select Organics, Angela's Blue, and PP Lost Seed Co, along with Swiss Giant, which all seem to be succeptible. On the right of the bed is Delta Louisa and Oregon Spring, both of which seem resistant. One line from the Jovan accessions (my research centre acquisitions) was an unknown Powdery Resistant Snow Pea, a survivor of the centre's Powdery chamber of death. It has been reluctant to germinate - of 5 seeds sown in Septenber only one survived - a subsequent resowing of 4 seeds yielded nothing. So I'm hoping for a good crop of seed from the one remaining plant. However, a bit bleary the other morning, I absent-mindedly emasculated one of its two flowers - shock horror! I've crossed it to a purple podded, so hopefully it takes and at least I will get something useful out of the error.

In search of A, the anthocyanin gene

To get reds and purples in peas, the starting gene is A, a dominant gene that controls anthocyanin production, responsible for many of the blue purple and red colours in plants. Other genes turn on the expression of this in various parts of the plant. And some genes turn it off, even when the plant carries A.
Why is this important? To get a stable line of coloured peas, having A contributed by both parents means you don't have to search for it in the offspring - every child plant will carry AA. So when I cross a Purple Podded with a snow pea, if the snow pea carries A, the numbers of crossed offspring i need to grow in subsequent generations is reduced. I only have to search for the other genes. This will influence the grow out strategies in future seasons.

A normal indicator of A is purple or red colouration somewhere in the plant - the leaf axils, the flowers, the sepals, or even the seed - if they are red or purple or brown, then the plant carries A. For example, my Golden Podded pea has yellow pedicels and sepals, but I can tell it carries A because it has purple leaf axils and petals.

 But there are lots of genes that influence colour of flowers and other bits, some acting alone, others in combination with other genes. A bit of a search on the John Innes database showed the following possibilities, amongst others

Genes am1 and am2 inhibit colour expression in flowers even if A is present.

b gives rose pink flowers and an effect on axil and seed coat colours, and axil pigmentation is reduced from purple to red. For example, the Golden Podded above looks a bit reddish to me - must compare with some others I've got growing.

Cit gives a citrus yellow flower - interacts with gene Cm to give "a light dull ocher with faint salmon hue."
cfg gives greenish flowers, and rub gives brick red wings on the flower.

So lots of material to play with out there.
 Unfortunately, all of my lines so far have either purple or white flowers - will have a close look over the next few days to see if there are any of these aberations lurking in the patch.

The Characteristics

OK, So I'm after a coloured snowpea. Just cross a purple podded pea with a snow pea - Bingo! But it's not that simple. There are four (maybe five) different pod colours - Green (normal chlorophyll), purple (anthocyanin present) and yellow (no chlorophyll in the pods) and red (a combination of yellow and purple). An orange pod gene exists, according to the John Innes  Pisum database, but I haven't seen it mentioned in any seed catalogues or breeding publications, so I don't think I'll be getting my hands on that germplasm any time soon.

Pod colour and shape were a couple of the characteristics studied by Mendel. There is a brief description along with some photos on the JI site, here.

Chlorophyll is either switched on or off by the dominant gene Gp, giving either green (Gp) or yellow (gp) pods.
A young Golden Podded

But purple is a different matter. You need one gene to turn on anthcyanin production (A). Then other genes turn on its distribution across the plant, that is, where it gets expressed. To get full purple pods, you need the dominant genes Pu and Pur. Other genes give purple splodges in the leaf axils, purple flowers and purple or brown in the seed coats.

Fibre in the pods, or more correctly lack of fibre in the pods is what makes a snowpea a snowpea. Fibre is controlled by two dominant genes, V and P. V makes the pod relatively smooth, v makes the pod clasp the contained peas, giving a lumpy pod.

So to get a purple podded snow pea from a purple podded pea and a snow pea cross, you need to get three dominant genes for purple pod combining with two recessive genes for low fibre. To get this in one go from a cross if the parents don't share any of these genes is a tall order - 9/4096, or about 1 in 500.

If you want to include any other characterisitcs - say dwarf growth form, double flowers (gives more production) or disease resistance, unless both parents have that gene, the chances diminish considerably.

Powdery mildew is a bit of a problem where I garden, so that gene (or genes, as it turns out) would be good.

I can reduce the odds if I can use parents that share some of these genes. But there are no purple podded low fibre peas, all of the purple podded peas I have are all tall, single flowered, and they all seem to be subject to powdery mildew. One variety (PP Lost Seed Company) is a bit earlier than the others so I have used it for a number of my early crosses - maybe it will confer earliness to its offspring.

On the snow pea side, Yakumo has purple flowers, showing it carries the A gene, but is tall, subject to disease, and in my observations, is only single flowered. But since it carries A, if I did a cross to a purple podded, I would be assured that all the offspring would carry A, improving my chances of getting a PPSP by four.

Melting Mammoth has double flowers, but probably doesn't carry the A gene. It is also subject to powdery.

Delta Louisa is a dwarf, has purple flowers (A), is double flowered and is powdery mildew resistant - a good candidate for one of the parents.

I'm also growing Oregon Spring - a double flowered white dwarf, which also looks like it is powdery resistant, and Swiss Giant, which I haven't grown before, but which looks to be double flowered and purple flowered, another good candidate for parenthood. I will have to check for disease resistance as the season progresses.

13 November 2011

The tools

I'm working on getting my equipment requirements together - something to do the emasculation on the female parent (removal of the pollen before it sheds), transfer of pollen from the male parent, labelling so you don't forget what you've done, and something to keep records in, so you know what you've done, and what you might need to do.

So I've been assembling my tool kit. A few more practised breeders put me on the right track. I started using a scalpel (Rebsie's weapon of choice, I believe), but juggling the flower parts, and manipulating the scalpel to prise apart the sepals and petals and excise the stamens had me somewhat concerned about slicing my fingers or hand open.

So I went online and purchased a number of different forceps - fine points in straight, curved and offset, a set of reverse action fine points (squeeze to open), and a set of medium point regulars. The reverse action ones (Carol Deppe recommends these) I found hard to use. The curved points are great, the curve seems to make manipulating the bits easier, and doesn't obscure you vision of the all the little bits. Handy for nipping off the redundant flower buds as well.

I got mine online from Australian Entomological Supplies - no connection, but when someone does a good job, its worth letting people know. Their prices were good, service was fine, and they have a sense of humour - the confirming email  raised quite a chuckle when I received it. And the product has so far given good service. At around $10 per unit, I can replace 'em relatively cheaply.

And to sterilise and clean the instruments, a screw top specimen jar full of methylated spirits.

For labelling the pollinated buds I use a bit of light garden twine loosely tied around the base of the bud, and an aluminium plant label - the thin soft sort that you can emboss with a ballpoint - affixed to the node below the pollinated bud with a thin bit of wire. I've even taken to writing over the label with a permanent marker to make the labels stand out a bit in the tangle of stalks and leaves.

To keep a record of my pollination activities I thought I would celebrate and rather than keep records in the cheap exercise books I use for my vege garden records, I lashed out and got a couple of Moleskine extra large grid square notebooks. Expensive, but hey, I'm worth it. Grids make it easy to keep schematic garden maps.

05 November 2011

The pea parents

In early September I planted the following coloured peas as parents for my breeding program
Purple Podded (Select Organics)
Angela's Blue
Purple Podded (Diggers)
Purple Podded (The Lost Seed)
Golden Podded (Diggers)

And these edible podded peas:
Melting Mammoth (Eden)
Delta Louisa (Green Circle Organics)
Dwarf Sugar Snap (Eden Seeds)
Oregon Spring (from littlegarden, a member at ozgrow)
and 4 other unknown snowpeas from other members at ozgrow, one just called chinese snowpea, and another labelled by me as USPPR - Unknown Snow Pea Powdery Resistant from a research collection which had survived the powdery mildew chamber of death.

By chance I had some Melting Mammoths growing for a food crop - a slice of luck since they are double flowered, and one aberrant plant had purple flowers and double flowers. It had purple colouration in the leaf axils, another indicator that it was a carrier of the A gene, responsible for anthocyanin production in peas.

So why all these parents?

Pisum breeding 101 (Skip this if you are familiar with pea genetics) Rebsie Fairholm's daughterofthesoil blog has a much more detailed account)
Peas are inbreeders. A pea flower pollinates itself (most of the time) so its genes can only combine with itself. Handy if you want to keep a line of peas pure from generation to generation - you just do nothing, and collect the seed at the end of the season.

But if you want to combine some characteristics from another variety of peas - edible pods for example, or a different pod colour, then you have to manually cross the varieties by hand. Early one morning when the pea is in bud and the flower hasn't opened, you sneak out with some fine forceps, ease the unopened petals apart, split open the keel that contains the reproductive parts, and gently pluck off the pollen bearing stamens before they have had a chance to shed pollen and self-fertilise the flower. Then go to a more mature flower on the other variety of pea, open it in the same way, and pluck or scrape some pollen onto your forceps. Back at the emasculated plant, you gently place the pollen on the end of the female reproductive part, the stigma. You then fold the petals closed, and wait to see if your pollination has been successful.

But how do you decide what to cross with what?
That's about pea genetics, another post I'm afraid.

04 November 2011

The cunning plan

I've been growing snowpeas for a few years now - Yakumo, Melting Mammoth, and some other generic snowpeas. After doing a bit of reading, I realised a snow pea ain't just a snow pea. There are:
  • genes for extra large pods, (I think Yakumo carries these, but I've never grown them as big as some of my correspondents); 
  • genes for multiple flowers per node (Melting Mammoth has this but Yakumo doesn't - in fact there are two different genes for flower number, but more genetics later); 
  • genes for colour (purple pods requires 3 different genes for full expression, yellow pods is a single recessive gene, and red pods comes from a combination of purple and yellow); 
  • genes for disease resistance - powdery mildew is a problem here and there are two different genes for powdery resistance;
  • genes for stem length - 3 or more, I think, leading to degrees of dwarfism - I prefer my peas to grow less than 2 metres high so I can harvest them, and don't have to struggle with hefty supports;
  • genes for snow pea (lack of parchment in the pod) and sugar snap pea (extra thick pod wall)

No doubt there are all sorts of genes for flavour, sweetness, etc but  I can't find them on the  John Innes Pisum Gene Database

So, my dream pea:
A sweet, multiflowered, coloured, large podded, disease resistant, semi-dwarf, tasty snow pea - let the breeding begin!

03 November 2011

Adventures with Mendel: vegetable breeding projects

Last year, I grew out some dwarf tomato breeding lines for the Dwarf Project, an amateur breeding program to develop a greater range of dwarf tomatoes.
I got interested in breeding vegetable varieties, read Carol Deppes's "Breed Your Own Vegetable Varieties" and was hooked.
So this spring I sowed a couple of dozen pea varieties to start another breeding project looking for some different coloured snow peas. Its possible to buy yellow podded (and now purple podded) snow peas in the northern hemisphere - they just can't be easily imported into Australia.
A UK seed company has devveloped a purple podded snow pea, and Rebsie Fairholm an amateur breeder in the UK has developed a red podded pea, and is trying to get a red podded snow pea.
More on the genetics in a later post.