14 December 2012

Male sterility in carrots - some photos

I've got a few pictures of carrot flowers showing the differences between normal and male sterile flower heads.

This is the flowering carrot patch.

 Here's a normal flower head or umbel. The emergent male stamens can be seen like a 'fuzz' over the top of the umbel.


This plant with coloured flowers doesn't appear to have any stamens.

This plant with coloured flowers has coloured stamens.


One problem with spotting CMS is the development stage of the flowers needs to be right to be able to see the stamens. In addition, production of pollen isn't really obvious.In tomatoes for example, pollen production is pretty easy to see, but in carrots, even in plants that I know are male fertile I can't really see pollen at all.

Here's hoping CMS, in my carrots at least, is indicated by the absence of stamens.

12 December 2012

Some Carrot (and other crop) Breeding Concerns

Carrots need to have a wide gene pool in the population or after a number of generations, inbreeding depression may occur resulting in poor, unproductive plants.  So it’s not a good idea to collect seed from only one or two plants - just like I have done with my self-seeded Baby carrots. So how many should you use? Best advice is a couple of hundred plants, but a minimum of around 50 is about as low as you should go.
I need to make a slight diversion. Hybrids, crosses between different varieties of the same vegetable, are known to be desirable. They often have better vigour than either parent, so modern agriculture has really focussed on the development of hybrid varieties. For inbreeders like tomatoes, this isn’t too hard- remove the pollen bearing bits from a flower before it has properly opened, get some pollen from another variety, transfer it to the first plant, and wait for fruits and seeds to develop. Each fruit produces numerous seeds, and each of these child plants will produce lots of fruit for market. So it’s commercially viable to produce F1 hybrid tomatoes year after year by crossing the original parents each year to produce new F1 seed.

But some vegetables, like carrots and parsnips are problematic. You need to have a big population of plants to collect seed from, the individual flowers are tiny, and they are bunched together in big bundles called umbels (thus the scientific name for this family of plants, the Umbellifereae.) So ensuring that the plant doesn’t pollinate itself is next to impossible. You could isolate individual flowers in the flowerhead, remove the pollen, and transfer pollen from another variety, but that would only give you one seed for each crossed flower, producing only one hybrid carrot for market – not a viable concern, really, and not enough to plant out a whole field of carrots or parsnips.

So how come some seed sellers advertise F1 hybrid carrots and parsnips? How do they ensure that every seed is the cross between two parent varieties?

It just so happens that there is a mutant form of some vegetables that don’t produce pollen. All the rest of the flower apparatus is in working order, they just don’t produce pollen. This is known as cytoplasmic male sterility ( I'll do a full post on this later). If this form is one of the parents, then the seed collected from these must have been pollinated by another plant. So grow one row of pollen free parsnips next to a row of a pollen producing variety, and only collect seed from the pollen free ones. Easy! But because of the nature of cytoplasmic male sterility, none of the F1 children will be able to produce pollen – this is not a self sustaining population. Unless there is some pollen producing plants around, the crop will die out.

So this is not a desirable characteristic to introduce into a breeding population if you want to develop a new variety to share.
Unfortunately two of the coloured carrot varieties I was planning on to supply coloured genes for my project are hybrids – so I can’t incorporate them into my breeding mix. But I do have a couple of dozen white, a few yellow yellow, and a couple of  purple carrots to provide some color diversity - hope they work!

Coloured Carrot Project progress

Compared to my successes with coloured snow peas, progress on my root vegetables has been slow – that’s what happens when you start on biennial vegetable breeding.
I planted carrots a number of carrot varieties in the middle of summer last year – Harlequin F1 multicoloured, Purple Haze F1 (a purple skinned orange cored carrot),Lobbericher heritage yellow, Belgian White, French Round, Chantennay, the last of some old Three  Colours Purple that was lying around in the seed shoe box, and a scatter of Baby carrots, that have successfully self seeded for a number of generations, but from a relatively narrow gene pool, since I’ve had 2 or 3 go to seed for the last couple of years.

But some problems arose. First, the French Round didn’t emerge, and I unsuccessfully tried a few other small round carrots until I got a variety to germinate. The delay means they are now out of synch with the coloured varieties, and I don’t think I will be able to get a cross happening.

A further complication with the timing has to do with the approach I used, what Susan Ashworth in ‘Seed to Seed’ refers to as ‘autumn winter spring’ seed production. Some further explanation. A normal biennial root crop would go through the following sequence. Seed sown (or fallen on the ground) would germinate in spring, with damp soils, and warming temperatures. The plant grows over spring and summer, and as the seasons progress, develops a swollen root. Come autumn as temperatures drop the tops stop growing, and the plant hunkers down for the winter, with plenty of energy stored safely away in the root to fuel early growth next spring. When the next spring arrives, the plant switches to reproductive mode, growth restarts, but instead of putting energy into a storage root, it draws on that stored energy to develop flowers. These get pollinated in summer, develop seeds, which dry off over autumn, and are shed on the ground ready to start the cycle over again.

A gardener wanting vegetable seeds of the best quality would dig up the roots in winter, inspect for desirable characteristics and select the best roots for replanting (and eat the rejects). In early spring, replant the good ones, and let them cross pollinate to produce seed.

But what if I just wanted to cross some existing varieties and haven’t got 2 years? This 18 month cycle can be shortened by sowing in late summer, getting good growth to develop, leave the roots in the ground, and letting the plants flower normally in spring. I’m not doing any selection, just wanting to cross varieties at this stage, so I don’t need to inspect the roots.
But when I want to see the results of my cross, I’ll need to revert to the 2 year cycle.

A further complication is cytoplasmic male sterility. Time for another post.

09 December 2012

More onions

A few pics of my topset onion inflorescences.

Here's the normal case for my topsets - a little bunch of onion bulbils
Normal bulbils on topsets

But this year - and a bit over the last few years - I've spotted some flowers on my topsets. Info on inducing flowering in garlic, that can be encouraged to set flowers if properly manipulated can be found here.

No reason not to try it on my topsets. so this spring I've been de-bulbil-ing the inflorescences on my topsets. The close proximity of a few rows of flowering bunching onions might allow a bit of cross pollination, so who knows what might result.
Honeybee on the bunching onion flowers
There are lots of pollinators around, and there seems to be a few flowers on the topsets that have set seed. A few weeks will tell if I (and the bees) have been successful.

What looks like pollinated flowers on my topset onions