Category: Genetic diversity

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Bee immunity

We’ve spent some time on the big bee die off (although not on the mobile phones) as have many other blogs and newspaper articles. In the US, the problem has reached epidemic proportions and has raised serious concerns about the future of several crops that depend to a large degree on bee pollination. Unfortunately recent evidence seems to suggest that the problem, which has been called Colony Collapse Disorder (CCD) has been spotted in Europe, as well. The cause or causes of CCD are unknown, but the list includes the usual suspects ranging from transgenic crops and pathogens to global warming and newly developed pesticides. Oh yes, and cell phones.

So the e-publication of a paper due to appear in the Journal of Heredity 1 (behind a paywall) is timely. It describes the heritability and genetic variation of a gene called abaecin which is a key component of the immune system of bees.

Bees, like nearly all eukaryotes, have an innate immunity, but are generally thought to lack the additional adaptive immune response, which we and most other vertebrate species have. That is to say insects can’t get the ‘flu and respond by making specific antibodies to the virus (In fairness, the notion that insects do not have an adaptive immune system has been challenged recently by studies in Drosophila. 2 )

To find out whether abacein expression differed between bee populations, scientists at the US Department of Agriculture crossed several unrelated males into a homogeneous maternal background and then challenged the offspring with Paenibacillus larvae. This is the bacterium that causes American foulbrood, a widespread larval disease of bees. Subsequent measurements in affected larvae showed that the level of abaecin was moderately heritable but highly variable, differing by as much as 10,000 times between different lines. Why this is variation exists at all is a matter of speculation, but it might be due to selective pressures: an arms race between hosts and different pathogen strains or species.

At any rate an understanding of the components of the immune response in bees at the molecular level and the realization that there appears to exist considerable genetic variation that could be exploited would seem to offer one of the more promising approaches to selection for pathogen resistance. Whether that will stop CCD is anyone’s guess 3.

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Lactose tolerance: independent origins and strong selective pressure

Michael Kubisch has submitted another post, based on an article in Nature Genetics. Unfortunately the full article and a News and Views piece about it are behind a paywall. However, I’ve done some sleuthing to find a few links that give more details on the story, which I’ve added at the end. As Michael noted, the article is “not about genetic diversity of agricultural species, but how agriculture has affected human genetic diversity”. That’s good enough for us.

The ability to digest lactose, one of the primary carbohydrates in milk, varies widely among adult human populations. In some European countries nearly 90% of individuals can tolerate lactose, while the incidence in some Asian countries is as low as 1%. The inability to digest lactose is caused by a decline in lactase, the enzyme that breaks down lactose into sugars that can be absorbed into the blood stream. This decline starts shortly after weaning and most likely reflects the fact that until animals were domesticated, milk was simply not a staple of human diets. Lactose tolerance, or lactase persistence as it is sometimes called, in turn is facilitated by a continuous production of lactase throughout adulthood. Not surprisingly, lactase persistence appears to be closely linked to whether a population has traditionally practiced a pastoral or an agricultural lifestyle.

This new study examined the incidence of lactase persistence in several African populations. Based on analysis of genetic markers the authors of the study conclude that the trait appears to have evolved not only independently from Europe, but also more than once in Africa itself. Given that the prevalence of the trait is so high in some populations and domestication of milk-producing animals only goes back 12000 years or so, which is a mere blink of an eye in evolutionary times, milk consumption must have provided a significant benefit for human survival.

Those links:

 

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More sorghum for Zimbabwe

A press release from the Netherlands Organisation for Scientific Research is creating tiny ripples in the blogosphere because it suggests that fertilizer, rather than water, is what poor farmers in semi-arid regions of Zimbabwe need to improve their crops. That’s certainly one conclusion from the research of Dr Bongani Ncube, who successfully defended her doctoral dissertation 10 days ago. (Congratulations, Bongani.) More important, I think, is the demonstration that almost regardless of water, sorghum crops benefit enormously from a preceding grain legume. There’s an interaction with rainfall to be sure. In a dry year, cowpea yields more than groundnut or bambara groundnut, but sorghum is always better after a nitrogen-fixing legume. That’s not to say that farmers shouldn’t make use of a little artificial fertilizer if they can afford it. But a better strategy might be to grow a variety of grain legumes, to buffer any possible effects of rainfall, and then plant sorghum, using agricultural biodiversity instead of cash to increase the harvest.

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Cereals databases

Before I disappear for a few days of immersion in the First International Breadfruit Symposium back in Fiji, let me point to two somewhat complementary online resources on cereals genetic resources that I have come across – no doubt Jeremy will say and about time too – in the past couple of days.

The FIGS database brings together passport and evaluation data on bread wheat landraces from a number of the major genebanks and “allows the user to efficiently interrogate the data associated with this collection and provides the capacity to identify custom subsets of accessions with single and multiple trait(s) that may be of importance to breeding programs.” FIGS stands for “Focused Identification of Germplasm Strategy,” and the focus is on identifying material with resistance to abiotic and biotic stresses.

The other database is that of Israel’s Institute of Cereal Crop Improvement, which includes information on accessions of wild cereal relatives collected over the past 30 years. Again, there’s a particular focus on data on disease resistance.

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Local and exotic crops in Africa

The long dry spell throughout much of February and March, caused by an unexpected El Nino that kept the main rain belt to the north of Zimbabwe, will cause serious hardship in significant areas of the country.

That’s not the only thing, of course, but an article from the Harare Herald 5 makes a plea for farmers to grow local indigenous grains such as “sorghum, mhunga and rapoko” rather than watch maize “wilt and die four years out of five”.

It is a wonderful article, making lots of good points. That food-for-work programmes should be accompanied by intensive training on growing small grains, so that those who need it most can become self-reliant in food and maybe even sell a bit for income. That modern machinery makes preparation much easier, and it isn’t expensive. That an advertising campaign could make a virtue of sadza 6 the way grandmothers made it. That there are benefits for urban consumers too. And finally, “Variety is wonderful. But we should not be rejecting indigenous grains simply because they are not ‘modern’ or ‘Western.” We should be using them as well.”

I wonder whether anyone is listening?

The Ethiopian Herald, meanwhile, says green gram is becoming the crop of choice in Southern Wollo zone. A legume, green gram (Vigna radiata, maybe most familiar in the West as mung bean) improves soil fertility, ripens more rapidly and doubles or even triples incomes. One farmer is quoted as having replaced his teff crop with green gram, but if everybody does that, who is going to supply the teff flour for njera?