Agricultural Biodiversity Weblog
Agrobiodiversity is crops, livestock, foodways, microbes, pollinators, wild relatives …
Yesterday was Apple Day in the UK. Started ages ago ((We don’t need no stinkin’ research.)) by Common Ground to draw attention to the diversity of apples and the threats to their existence, it has grown in a great bowlful of treats around this time. Of course, it’s a bit late now, but here’s a Top Ten of orchards to visit. And a week ago, the Daily Telegraph was visiting Brogdale, waxing lyrical but making very little fuss about the impending sale of the collection.
I miss my apple trees.
More evidence of multiple independent domestication events. Previous work has shown such a pattern for rice in Asia and cucurbits in the America. Now it’s the turn of barley in Eurasia. A paper just out ((Saisho, Daisuke, Purugganan, Michael. (2007) Molecular phylogeography of domesticated barley traces expansion of agriculture in the Old World. Genetics.)) looked at both sequences of 5 genes and also morphological traits in a geographically widespread set of 250-odd landraces. ((From a Japanese university genebank.))
The results suggest that the crop was first domesticated 10,000 years ago somewhere in the Fertile Crescent, from whence it spread to Europe, North Africa and Ethiopia (the material from Ethiopia was somewhat distinct, as has already been documented). However, there was apparently also a second domestication, much later. It occurred in the region encompassing southern Central Asia, the eastern Iranian plataeau and the edge of the Indian subcontinent, and it is material from here that spread eastward starting maybe 2,500 years ago, possibly along the Silk Road, to give rise to the barleys of India, the Himalayas and China.
This is not an unusual pattern in Eurasian agricultural biodiversity. Sheep and cattle DNA data also show “two highly divergent lineages that distinguish European and Asian types, indicating a second independent evolution of these livestock species outside the Near East.” Not unusual, but somewhat puzzling. As the barley authors conclude:
It remains unclear why different cultures sought to re-invent these domesticated species several times rather than simply obtain them through diffusion from other farming societies.
The authors of the barley study speculate that the second domestication happened either because of the transmission of knowledge, or as an independent innovation. I find the second option a bit hard to take. Could it be that the results of the first domestication effort were just not adapted to conditions outside the Fertile Crescent, or there was a barrier to their diffusion? Or maybe it was just a matter of pride for the inhabitants of the Iranian plateau to have their own agrobiodiversity?
Almost a year ago I blogged about a trial of perennial wheat being planted at Texas A&M University by Dr Charlie Rush. Well, the results are in now, and they’re encouraging. According to a press release, the grazing (they do that with wheat in Texas) was as good as annual wheat, and the seed yield about half. Another part of the study is getting under way, crossing the perennial wheats with regionally adapted varieties to try and produce perennial wheats that are better suited to specific conditions. And more detailed investigation of the perennial wheats will continue.
The really good news, as far as I am concerned, is that Dr Rush is now collaborating with Dr Stan Cox at The Land Institute. The scientists there have been such pioneers in perennial polyculture, I was kind of peeved that the first news from Texas A&M ignored them. It is very heartening to see mainstream scientists recognizing The Land Institute’s contributions and expertise. There’s also apparently been interest in the perennial wheats from what Texas A&M calls the Jon Innes Centre in Norwich, England. ((It is actually the John Innes Centre, with 1.3 million Google hits, versus the five for Jon Innes Centre.)) It is hard to tell what the JIC wants with perennial wheats; the release says something about habitat for wild birds. No doubt all part of the UK’s marvellous biodiversity conservation plan.
And in other wheat news, two rather heavy-duty papers about molecular biology. The first is a review of molecular markers in wheat breeding. ((Landjeva, Svetlana et al. (2007) Molecular markers: actual and potential contributions to wheat genome characterization and breeding. Euphytica, 156: 271-296. http://dx.doi.org/10.1007/s10681-007-9371-0.)) If you’re into this sort of stuff, you don’t need this review. If you aren’t, it gives a reasonable history and summary and might help you to scythe your way through the thickets of jargon, acronyms and abbreviations. My main objection is the claim that “large-scale genome characterization by DNA-fingerprinting has revealed no declining trends in the molecular genetic diversity in wheat as a consequence of modern intensive breeding thus opposing the genetic ‘erosion’ hypothesis”, which takes a very narrow view of the genetic erosion hypothesis indeed.
And coming right along to bolster my belief, a paper showing that synthetic wheats are a valuable source of traits to improve varieties for baking and milling. ((Kunert, Antje et al. (2007) AB-QTL analysis in winter wheat: I. Synthetic hexaploid wheat (T. turgidum ssp. dicoccoides — T. tauschii) as a source of favourable alleles for milling and baking quality traits. Theoretical and Applied Genetics, 115: 683-695. http://dx.doi.org/10.1007/s00122-007-0600-7.)) It is much easier to cross modern wheats with synthetic wheats (because they contain the same number of chromosome sets, six) than it is to cross modern wheats with either wild relatives or ancient wheats (which contain four or two sets). Kunert and colleagues crossed two wild species, revealing interesting genetic traits to improve qualities such as the amount of protein and the resistance to sprouting in storage, which can now be bred into modern wheats.
My feeling is that if all the genetic diversity breeders need were present in modern wheats, as Landjeva seems to think, then other scientists would not be spending considerable time and effort to create synthetic wheats from wild relatives in order to use them in breeding programmes.
Ah, synchronicity. While Luigi was fleetingly confused about rhizobia and other bacterial symbionts of pigeonpeas, I was pondering one of the more interesting blog posts — and papers — I have read in a long time, also about rhizobia. Those are the bacteria that “infect” leguminous plants, forming nodules on the roots. In the nodules the bacteria “fix” nitrogen gas, from the air, into a form plants can use. In exchange, as it were, the plants supply the bacteria with a safe home and some of the food the plants have photosynthesized. Some rhizobia do a better job than others, and many are completely useless at fixing nitrogen. Better yet, the plants know, and send more food to the nodules fixing the most nitrogen.
Now, the tricky part.
Modern agriculture does not usually apply nitrogen to leguminous crops. But there can be considerable carry-over from the preceding crop. So, two possibilities arise. Maybe soybeans no longer respond to better nitrogen-fixing bacteria by sending more food their way, because they don’t really need the nitrogen. Or maybe more soil nitrogen means that the plant can afford to starve out all but the very best nitrogen fixers.
But why am I repeating all this? You cannot possibly do better than head over to Ford Denison’s blog, where he does a much better job than me of explaining the significance of his results. The paper is also discussed in Nature News.
Spoiler (aka don’t bother me with the details): modern varieties do very poorly when inoculated with a mixture of good and bad nitrogen fixers. It is as if they simply cannot tell the difference and feed both equally.
Stunning new idea: If modern varieties tolerate low quality rhizobia, then low quality rhizobia are going to proliferate in the soil, doing nobody any good. So why not deliberately breed legume crops to impose very strict sanctions against poorly-performing rhizobia strains? Long term this would enrich the soil with top-notch fixers.
“Genetic endemism” is northern Eurasian cattle.