And Now For Something Completely Different

- which has nothing to do with the Liberty Bell, John Philip Sousa or Monty Python in this instance. I mentioned previously that interspecies crosses have a useful role to play in the development of new crops.

Well, here's an illustration of what might be achieved and some of the challenges inherent in this sort of work. Not in this case a root crop - I do actually allow myself the luxury of growing a few other plants. This was a little impromptu experiment in creating a hardier squash.

Chilacayote (Cucurbita ficifolia) is by far the most vigorous and cool weather tolerant squash that will grow outdoors in Britain. As the autumn proceeds, chilacayote keeps on going, setting fruit, whereas none of the other squashes can cope with the cool wet weather that typifies our late autumns - they splutter to an undignified end months earlier. I thought it would be interesting to try and combine the exuberance and fecundity of the chilacayote with the culinary superiority of the related species C. maxima. Chilacayote also has a knife-bustingly tough shell which allows it be stored for ages - several years, in fact. That, too, would be a useful characteristic to transfer to a better quality squash.

In 2007 I pollinated a female chilacayote flower with a male C. maxima variety. To my surprise, the fruit developed and contained seeds which were intermediate between the two parental types. I planted these the following year. Several germinated and the F1 seedlings grew away vigorously, with an initial appearance somewhat like C. maxima:

I planted them out after the last frosts and they romped away.

They produced plenty of female flowers, but male flowers were rare and the anthers didn't seem to produce any pollen. I pollinated individual female flowers with pollen from either C.maxima or C. ficifolia - a process known as backcrossing. Plenty of fruits developed on the backcrossed plants, although no viable seeds seem to have been formed in any of the fruits I have examined so far.

Shame. I've still got a few left though and I daresay I'll open them up this spring, just in case. I'm tempted to blag my way into a local institute of higher education and see whether I can regenerate the plants in vitro using some of the fruit flesh, which is, of course, maternal material.

Anyway, here's the family tree laid out in the way beloved of plant breeders, with mum on the left, dad on the right and some of the interspecies offspring beneath in all their motley glory:

So that's as far as my squash breeding project has got to date. I contacted a cucurbit breeder in Slovenia, Dr Anton Ivancic, who expressed surprise that I had managed to produce any F1 seedlings at all - he normally has to excise the embryos and grow them in nutrient media before planting them out. He looked at my pictures and concluded that that there were definitely some C. maxima genes in there. His paper on Cucurbita ficifolia x maxima is here. The flesh of my fruits appears to be identical to C.ficifolia; the only difference that is obvious seems to be in the yellow skin colour.

I'm particularly fond of one of these fruits, which is large and smooth and shapely. I fondle it with a frequency that borders on the peculiar. Not so much the love that dare not speak its name as the love that doesn't yet have a name - ficifoliaphilia perhaps?

There is a link, somewhat contentious, between chilacayote and tuber crops: spermidine synthase genes derived from C.ficifolia have been used to genetically modify sweetpotatoes in Japan. The resultant transgenic plants are apparently more resistant to chilling injury and oxidative stress. They are also able to develop storage roots (the bit you eat) in lower light levels than normal sweetpotatoes. No mention of what they taste like though. So whatever your opinion on GM technology, it at least shows that C. ficifolia is a plant with some very useful attributes. Maybe if I keep crossing it with any other squashes that I happen to be growing in the patch, I might just get lucky and create a delicious new squash that climbs trees, thrives in cool weather and keeps for years. I have a dream............


IAP said…
That is a beauty! How do you obtain stability after the first generation?
I occasionally get an illicit Cucurbit lovechild coming up in the plot, possibly from reverted F1 seeds that have survived the composting process. I'll let them live if their location is not inconvenient, but unfortunately the fruit usually seem to retain the worst characteristics of both parents - ugliness, smallness, toughness, and tastelessness. Still, one day the toast may land butter side up.
threnody said…
That's really interesting--I've recently aquired some C.ficifolia seeds to try out in my garden and see if they are worthwhile. That is a gorgeous yellow squash that you are holding.
Rhizowen said…
Hi Ian
Thanks. I'm rather pleased with that one.
As regards stability in the F2 and beyond, the simple answer is I don't know. I would guess that if I managed to produce an F2 (sadly unlikely) there would be all sorts of weird assortments of the two genomes. If the problem of male sterility could be overcome I would choose the plant(s) with the best qualities and self them and keep selecting for desirable characteristics until some sort of stability was achieved. The majority would be, as you've noted, pretty inferior.

Ben Gabel of Real seeds has done something similar C. maxima x moschata to create "Ben's Winter Monster". It's described somewhere on the Real seeds website (I think). I must try and grow it this year.

Hi Threnody

If you're in the tropics, then chilacayote will climb up the trees and you'll have huge fruits swinging above your head - watch out.
Although the mature fruits are very sweet and stringy, they are apparently valued for their ability to control blood sugar levels. Immature fruits are nice fried.
Rhizowen said…
Threnody - the seeds are very tasty too - heat them in a pan or skillet and they tend to puff up a bit which makes it easier to extract them from the shells.
Anonymous said…
that's a lovely dream!