25 November 2012

A new onion project

Onions (Allium cepa)come in all sorts. Bulbs, big and small, long lasting and eat now, raw and cooking. For the purposes of growing onions, bulbing onions are divided into groups depending on the trigger they need to start forming bulbs - short day, medium day and long day are the usual designations. Growers in the tropics have problems growing the long keeping varieties, most of which need long days to trigger bulbs. (Actually onions respond to the period of darkness, rather than light, but let's ignore that for the moment.) This is all very messy.

I've never had much luck with onions. Timing is everything. Here in Bendigo I can choose to grow any variety I like, summer night and day periods are sufficiently different to allow me to grow short, medium and long day varieties. But I never get the sowing time right, the seedlings sit and sulk through early spring, they get swamped by weeds when young, and last year, my alliums (garlic and leeks) were struck with a failure to thrive disease, that I'm yet to diagnose.

But there is another candidate on the patch - topset or multiplying onions. These hardy individuals grow in bunches, and instead of forming flower heads, they develop little bunches of new onion bulbs at the tips of the stalks. There is some confusion about the exact phylogeny of topsets, some suggesting they are a distinct variety of A.cepa, or perhaps a hybrid between A.cepa and Allium fistulosum, the bunching or welsh onion.

There are as many names as there are cultivars - walking onions, topset onions, multiplying onions, Egyptian onions. (Potato onions are probably in the same group, but don't seem to top set bulbils). Some of these set small basal  bulbs and die down, some set small bulbs and keep growing. They come in red and white and brown. They are not really sold in Australia, and I've only ever seen them once in a nursery. Mine don't set bulbs at all really, just a minor thickening of the base. Every generation is the same, because they are vegetatively propagated.

But the big advantage of these is they grow throughout the year for me. They were totally unaffected by the disease I got, they take no trouble, they're always there in the garden, and they are so easy to propagate. Last year I noticed that some of the topset formations had a few flowers scattered through the bulbils. I did nothing. But in the last 12 months I've been reading up on alliums. Garlic also doesn't set seed. But some researchers have been inducing flowering in topset garlic (which produces little bulbils on top of the stem, just like topset onions) by removing the bulbils as soon as they form. This fools the plant into thinking it needs to reproduce, and since the bulbils aren't working, maybe they should indeed produce some fertile flowers. I wondered if this would work with my topset onions. I've spent several hours over the last week picking bulbils out of my topsets. And the flowers look like they are fertile. Good news.

A further problem with some plants that are reluctant to produce flowers can be the inability to produce viable pollen, or self incompatibility issues - where the pollen from the same plant can't pollinate its own flowers. Since all my topsets, despite being in lots of distinct clumps are all the same plant genetically, there might be incompatibility issues. By chance, I'm also growing some Japanese bunching onions, A. fistulosum, which is flowering profusely. Bees are all over the big round flower heads, and with luck, I might get a bit cross pollination, if the topsets are self incompatible (which I don't know) Seems like a bit of lucky insurance.
So what might I get out of these if they set seed?

Who knows! Maybe I'll get bigger more robust plants. Apparently lots of vegetatively propagated plants build up a virus load, which is transmitted from mother to daughter. By going to seed, its possible to shed this viral load, leading to increased vigour in the offspring. Or maybe some genetic recombination wil occur and some ancient ancestral traits will emerge. Who knows how long these things have gone without reproducing? I've been inspired by the work of Kelly Winterton, who has been quietly developing extraordinary potato onions in his backyard in Utah.

I'm not sure where mine came from. My mum had them in her garden, and passed them on to me, but I think they died out, and I replaced them with some material I bought in Albury when I lived there 15 or so years ago.

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