20 March 2012

TPS - True Potato Seed

True potato seed (TPS) is the seed produced from the fruits of flowering potato plants that have gone through sexual reproduction. So called 'seed potatoes' that are commercially available, are not really seeds, but tubers from a selected potato line - they are identical to the parent plant, since it is just vegetative propagation. There is virtually no chance of a different potato arising from this sort of propagation - indeed, that is just the point - commercial growers want reliability in the crop they are producing.

But TPS introduces genetic variability. And a quirk of most potatoes is their polyploidy. Most normal plants have pairs of chromosomes. But most 'modern' potatoes are tetraploid, they have double the number of chromosomes, which gives rise to all sorts of genetic mixing if they reproduce sexually through the flowering-cross polllination-setting seed route. This genetic mixing has the possibility of developing all sorts of interesting characteristics in the offspring.

It is possible to cross potatoes, using a similar method to tomatoes - emasculate the female parent by removing the anthers pefore they shed pollen, collect pollen from the male parent, then apply it to female parent stigma. Rather than go through all the mechanics of this, check out the information at Tom Wagner's tater-mater blog, or Rebsie Fairholm's excellent daughterofthesoil blog.

Alternatively, if you have a variety that flowers readily (not all do) and that has no self-compatibility problems (many do), and that retains its fruits to maturity, you can just see what turns up. That's what I've done.

My TPS, in this generation at least, is from self pollinated Pinkeye potatoes, derived from some certified seed tubers I purchased at my local nursery (sourced from Goodmans Seeds, if I remember correctly). There is a slight chance they have crossed with another self-propagated potato that just came up in my garden nearby, which also set a fruit, but it wasn't flowering at the same time as the Pinkeyes, so the chances of an intervariety cross is slim.

The fruits mature a bit like small hard green tomatoes, (sorry, the pic is a bit blurry) and the seed is fermented out like tomato seed - squeeze into a small container like an egg cup, leave open to the air for a few days until it ferments, then rinse the seed out in a tea strainer, and dry on a bit of paper towel.

Sow it like tomato seed, and prick out. That's where I am now - a bit risky at the start of autumn, since these little plants really need to set a tuber between now and winter, so I have something to plant out next spring.

This involves a bit of 'hilling up' in the pots, covering the lower leaves to induce tuberisation. Let the experiment continue.

I'm also intending on growing out some plants to do a bit of crossing next season. A greengrocer in Melbourne stocks a good range of vegetables, so I bought a couple of tubers of all their interesting non-standard lines - Pink Fir Apple, Virginia Rose, Blue Zarr, Royal Blue (which look the same), and Gold Finger.
Hopefully they will flower, and I'll get some more interesting colours to throw into the mix.
I've already got Purple Congo and another couple growing in the greenhouse, so I'll see what happens with their flowering phenology over autumn/winter.

12 March 2012

Summer seed production

I've just harvested the five F1 growouts I tried as an experiment to see if I could sneek an additional generation into the growing year, and shorten my generation turnover time.
A bunch of seed didn't germinate - I think due to soil borne disease or rot. Lucky they were my excess 'wrong way' crosses.
Of the five plants that I grew in pots, I got 26 seed for one of the crosses from 3 plants, and 19 seed from two plants for the other cross. Not  a huge haul, but useful. Powdery mildew  struck the plants over the last few weeks, and the last of the pods on the plants were fertilised, but failed to develop. I was too busy to spray with potassium bicarbonate.

These F2 seeds will get sown in the next few days, with a potential F3 crop in 3 months. The odds that my purple snowpea is going to show in the F2 is a bit low.
From my PurplePod X PurpleFloweredMammoth cross, both carry A, that turns on purple, so that's covered. But I'm also looking for purple in the pods, that needs  Pu_Pur_ (doesn't matter at this stage if they are heterozygous), and ppvv the two recessive genes for non-fiberous pods (so they need to be homozygous) so the probability is 3/4 X 3/4 X 1/4 X 1/4 = 9/256, say around 1 in 30 for any given plant, and I've got 26 seeds. Twice that number of seeds would have been useful, but the chances aren't too bad.

My PurplePodded X MeltingMammoth has less seeds and is also less likely since MM doesn't carry A. So the odds for a purple snow from any one of the F2 seeds is 9/1024, or around 1/100. With only 19 seeds my chances aren't too good in this generation.

None of these parents were powdery mildew resistant, so I will either have to cross in a subsequent generation, or hope that one of my other crosses (which I'm only growing the F1s of this autumn) carries the genes for that trait.

With a bit of luck, some of the PP X PFM F2s will also inherit the double flower gene from the PFM parent.

On a side note, the Purple Flowered Mammoth was a mis labelled plant that came up in a Melting Mammoth batch - I might have interplanted it with some seed I got from a 'net buddy (Jayendra) to fill in some gaps in the patch, but I didn't keep good records that day, so it will remain as Purple Flowered Mammoth (but I suspect it's really some of Jay's Yakumo line - but Jay's seed is a different colour to my purchased Yakumo, so I don't know what's going on. Doesn't matter, it was a nice snow pea with big pods).