In my quest to create the perfect sweetpotato for our unsympathetic climate, I've been doing a bit of hunting around for some of its wild relatives. This is an approach used by proper plant breeders to introduce genes for disease resistance and adaptability into major crops. I'm not sure whether this means that I'm now dragging myself up to their level, or whether the plant breeding brethren (and sistren) will be tainted by association with my madcap antics. If you don't tell, I won't either.
Mecha-meck or bigroot morning glory (Ipomoea pandurata) is one of the most cold tolerant sweetpotato relatives, being found in parts of the Eastern USA and Canada which have much colder winters than we do here in the UK. Its roots are edible and taste, unsurprisingly, like a sweetpotato, although several references mention that they are often somewhat bitter. Although said roots can survive sub-zero temperatures with ease, it doesn't mean that the vines that issue from them are going to like our cloudy, cool summers. It's what I call the Maypop Paradox, after the "hardy" passionflower Passiflora incarnata. It comes from the same neck of the woods as mecha-meck and although it can easily survive our laughably mild winters in a dormant state, our summers (or lack thereof) are fatal to it. At least whenever I try and grow it. I'm reminded of Mark Twain's supposed quip about the coldest winter he ever spent being a summer in San Francisco. He should have visited Cornwall. Anyway, my guess is that mecha-meck is cast in the same mould and at best its vigour will be severely checked by that lack of summer warmth. Time will tell.
It does, however, have a close relative, Ipomoea leptophylla, which grows out in the western USA at quite high altitudes, up to 2000 metres or so in Colorado, for instance. It has been described variously as delicious, or as a famine food - take your pick. One of I. leptophylla's vernacular names is "manroot" - I suggest caution when Googling that name and make no claims expressed or implied as to what sort of images or text may storm your computer as a result.
Rather than a vine, I. leptophylla is distinctly bushy, which might make it easier to manage as a garden plant. It might take cooler summer temperatures in its stride. That set me thinking about how it might be fun to have a go at crossing the two species and seeing what comes out. That's a lot of mights for one paragraph, but three mights don't make me wrong do they?
These are the seeds of mecha-meck, looking like shaggy understudies for Cousin Itt from The Addams Family. I'm not sure what the purpose of the coiffure is - the seeds are about 1cm long - quite substantial - and I can't imagine that even this amount of fluff would carry them very far on the breeze.
Here are some mecha-meck seedlings with the distinctive delta wing cotyledons which all the Ipomoea species I've ever grown seem to display.
Sweetpotato is a hexaploid with six sets of each chromosome (2n = 6x = 90) whereas mecha-meck and manroot are both diploid (2n = 30); most of the literature suggests that interspecies crosses between sweetpotato and its wild relatives are hard to achieve anyway - never mind the differences in ploidy - which isn't really what I wanted to hear. However, last year's impossibility is this year's commonplace: I recently came across a paper by some Chinese researchers where they had managed to do exactly this. The abstract is here. The actual paper lurks behind a paywall, thumbing its nose, no doubt, at us mere mortals who don't fancy spending $34 on the full text.
This idea of using I. pandurata to increase the cold hardiness of sweetpotato is nothing new - I'm merely ram-raiding the vaults of yesteryear and grabbing whatever takes my fancy. In a 1935 paper in the Journal of Heredity, M G Tioutine outlines his work on breeding sweetpotatoes in the USSR and goes on to describe his attempts at crossing I. batatas with I. pandurata. A few pods were formed, but there's no mention of whether they contained viable seeds or not. I haven't found any other papers referring to his further research on this front either. Judging by the fate of Vavilov, working as a plant breeder and geneticist at this time was not, perhaps, the safest career path in Soviet science. (There's more on Vavilov at Vaviblog - a great, great man).
Tovarishch Tioutine does, however, describe the roots of I. pandurata as tasting similar to Jerusalem artichokes, which doesn't sound so bad after all. Perhaps it's just a case of harvesting them young, before they become tainted with whatever it is that makes them bitter.
So all I need to do now is get hold of some I. leptophylla seeds, grow the plants to maturity, then set up an Ipomoea menage a trois with I. pandurata and the best adapted I. batatas varieties, including ones from the highest sweepotato plots in the Highlands of Papua New Guinea.
Should be an absolute breeze. In the meantime, I'm waiting on the universe to deliver me seeds of yet another Ipomoea: the fabled sweet-tasting, high altitude Andean species I. minuta. I'll throw that into the mix when it finally arrives. I don't know what the collective noun for a disparate bunch of ipomoeas is - could it be an entanglement? What I do know is that I'd like the chromosomes of this motley crew of morning glories to commingle and maybe create something interesting in subsequent generations. You say potato, but I say batatas - and I won't call the whole thing off.