The suggestion has just been published that leaf variegation may have evolved as a defence mechanism against being eaten. Variegated leaves look like they’ve already been attacked, so they’re avoided by pests. Working on an Ecuadorian rainforest floor aroid, researchers found that
While moths infested almost 8% of green leaves, they infested 1.6% of variegated ones and just 0.4% of those painted to look like they were variegated.
We’ve been keeping a weather-eye on the new strain of wheat stem rust called UG99 (it was isolated in Uganda in 1999) since very early in the history of this blog, trying to keep at least vaguely abreast of its spread and efforts to fight it. In truth, it has not been a very happy story, and if our coverage has dropped off just a bit, that may be because it can get tiresome crying wolf, no matter how much joy it might give us to be proved right.
Anyway, there’s been another outburst of interest, and while the news still isn’t good, it is fun to see how different people tell the story. First off, there’s The Hero :
Like the warrior Beowulf, subject of the Old English epic poem, [Norman] Borlaug slew a monster, saved his world and lived to a ripe old age. Like Beowulf, this old warrior of science has had to climb back into armour to battle the rise of a new monster. And once again, the world is looking to him for salvation.
Elizabeth Finkel, teller of that particular tale, certainly has a sense of drama. ((She’s also been busy lately.)) And she gives a very full account of the fight against wheat rusts in general. Across it all strides Borlaug, whom Finkel describes as “frail”. Any 95-year old is entitled to be frail, but my understanding is that he is in worse shape than that. How will the scientists and funders fare in his absence? I hope they redouble their efforts, in memoriam as it were.
Then there’s the army of soldier ants, selflessly toiling in defense of the greater good:
After several years of feverish work, scientists have identified a mere half-dozen genes that are immediately useful for protecting wheat from Ug99. Incorporating them into crops using conventional breeding techniques is a nine- to 12-year process that has only just begun. And that process will have to be repeated for each of the thousands of wheat varieties that is specially adapted to a particular region and climate.
Karen Kaplan’s story, in the LA Times, is as broad as Finkel’s, but paints a different picture. Borlaug doesn’t even get a name check. Instead, scientist after US scientist gets a brief moment to explain how complex and yet tedious the job is, how ill-prepared they were, how each depends on all the others, and how the rest of humanity depends on them. We need both stories, I think, scientist as individual hero and scientist as soldier ant, breakthrough and toil, and I hope readers get them.
Yet another narrative crops up, though. I’m not sure what to call it. Pot of Gold? Silver Lining? Unexpected Benefit?
Crop scientists have discovered a new threat to wheat crops within the United States, leading to a race to be the first to breed a resistant wheat plant, before there is trouble. Any outcome could have a big effect on related agriculture exchange traded funds (ETFs).
Setting aside all the guff about the threat being “new,” Tom Lydon, in Commodity Online, points his readers to two such exchange traded funds, noting that “fear that the fungus will cause widespread damage has caused short-term price spikes on world wheat markets”. In other words, there may be money to be made.
Why the current spate of interest? That’s hard to say. There have been meetings in Mexico and Syria, which account for the most recent spike in Google Trends. But nothing that I have noticed more recently than that. Just coincidence, perhaps. And in all the stories about how to deal with UG99, there’s one that has been conspicuous by its absence. Don’t Put All Your Eggs in One Basket.
Faced with the cost of controlling disease in monoculture, two solutions emerged – to keep producing new varieties and new fungicides. But both of these solutions led to the Red Queen problem in Lewis Carroll’s ‘Through the Looking Glass’: ‘Now, here, you see, it takes all the running you can do, to keep in the same place’. Mixtures of appropriate varieties, however, can restrict disease and increase yield reliably, without need for fungicides.
“It can be planted in farms because it does not compete for resources with corn, coffee or bananas and acts as a nitrogen-fixing agent in the soil. The mpingo is also considered a good luck tree by the Chagga people who live on the slopes of the Mt. Kilimanjaro.”
Faced with pessimistic predictions of the impact of climate change, it’s too easy to throw your hands up in the air and cry “there’s nothing to be done”. Or, as a few people still do, to throw your hands up in the air and cry “there’s no need to do anything”. But if they turn to the latest issue of Global Environmental Change, policy-makers, plant breeders and genebank managers should be able to throw their hands in the air with a cry of joy: “This is what we need to do.”
Percentage overlap between historical and 2025 (left), 2050 (middle), and 2075 (right) simulated growing season average temperature over African maize area. Dark blue colors represent 100% overlap between past and future climates, dark red colors represent 0% overlap.
The authors of Shifts in African crop climates by 2050, and the implications for crop improvement and genetic resources conservation are Marshall Burke and David Lobell of the Program on Food Security and the Environment, at Stanford University, and our own Luigi Guarino, wearing his Global Crop Diversity Trust hat. ((Burke, M., Lobell, D., & Guarino, L. (2009). Shifts in African crop climates by 2050, and the implications for crop improvement and genetic resources conservation Global Environmental Change DOI: 10.1016/j.gloenvcha.2009.04.003. And though the article is beyond a paywall, which is why I am quoting extensively, I’m sure one of the authors would be able to send you a reprint.))
The approach is quite straightforward. First, they ask how crop climates will change across Africa. This involves taking historical data for a particular place and comparing the climate there to the predictions of a whole bunch of climate change models. They then ask how quickly the predicted changes will push local climate outside the limits of recent local experience. In addition, they looked at different climates across the continent, asking whether future climates are currently present somewhere in the country, or elsewhere on the continent. The goal is
[T]o identify both future problem regions with no analogs on the continent in today’s climate, and countries whose current crop areas appear likely analogs to many future climates, with the latter case representing promising areas for genetic resource collection and preservation.
They do so for the three primary rain-fed crops of sub-Saharan Africa: maize, sorghum and pearl millet, which provide roughly a third of the calories consumed, and almost two-thirds in some countries.
The big predicted change of all the models is in temperature, which gets hotter almost everywhere, with much less agreement among the models of how much rainfall will change. Skipping over just how fast climates are changing (“rapidly”) and keeping in mind the large time lags involved in breeding crops suited to changed climates, Burke et al. warn that their results “suggest a pressing need to develop breeding programs that anticipate these rapidly warming growing environments.”
So there’s one thing people can do, now.
Where will the raw material for those breeding programmes come from? Genebanks, natch. Alas,
African cereals are often poorly represented in international genebanks, and national genebanks on the continent are frequently resource-constrained and not always representative of the crop genetic diversity in the country.
Burke, Lobell and Guarino look at the spatial distribution of climate analogues and calculate “self-overlap,” overlap of the extremes of projected climate with today’s climate within the country. ((Actually, with the average of the past 10 years of observed climate, long enough to average out extremes but short enough to capture the current climate.)) There’s a nifty graph of the overlap for each of the three crops in all the countries, but the take home message is that despite the lack of overlap in some places, there’s still enough variation that a country might be a good source of variability for its own needs. On the other hand, future temperature regimes are likely to be so hot that even those countries that have large self-overlaps will likely have to look outside their own borders for varieties that will thrive in their expected climates.
Many countries with low self-overlap nevertheless have five or more countries that overlap 75% with their new climates.
For these countries, breeding efforts to cope with warming could greatly benefit from accessing genetic resources beyond their own borders.
Something else to do, now.
There are, however, also countries, most of them in the Sahel, that have low self-overlap and fewer than 5 analogs in other countries. They’re already the hottest climates in Africa, and likely to become hotter, so it ought not to be a surprise that their options are going to be limited.
Unfortunately, primary centers of maize diversity outside Africa, such as in Mexico, enjoy much cooler climates than much of Africa. If breeding efforts cannot sustain yield for maize for these hottest climates in the face of warming temperatures, switches to potentially more heat- and drought-tolerant crops, such as sorghum and millet could be necessary.
Then there are the happy countries whose current climates contain analogues to many future novel climates. Their genetic diversity will be valuable for future breeding efforts. Are they safe?
Sudan, Nigeria, Cameroon, and Mozambique … are particularly poorly represented in national and international genebanks. The top ten analog countries for maize — those which overlap most with anticipated novel climates on the continent — each have fewer than 150 landrace accessions in major genebanks. These countries appear as particularly high priorities for urgent collection and conservation of maize genetic resources. … The results for sorghum and millet show qualitatively similar patterns as the results for maize.
There’s a lot more meat in the paper, which repays close reading. It really does contain evidence-based policy advice, on how best to make use of a limited pot of cash by setting the right priorities and establishing the right kinds of cooperative efforts.
Why the current spate of interest? That’s hard to say. There have been meetings in Mexico and Syria, which account for the most recent spike in 
