Category: Biotechnology

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Reinventing the wheel

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?

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Another thing CWR can do

Nitrification is the oxidation of ammonia to nitrite. It’s an important part of the nitrogen cycle and all that, but bad news for agriculture, because up to 70% of applied N fertilizer can be lost to plants this way. There are synthetic nitrification inhibitors out there (e.g. dicyandiamide), but now comes news that a wild relative of wheat is also pretty good at slowing down the process. Researchers have identified the bits of the genome involved in biological nitrification inhibition in Leymus racemosus, and have managed to get them to do their stuff in wheat too. ((Subbarao, G. et al. (2007) Can biological nitrification inhibition (BNI) genes from perennial Leymus racemosus (Triticeae) combat nitrification in wheat farming? Plant Soil 299:55-64.)) Is there nothing crop wild relatives can’t do?

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A history of viruses

We’re fond of reminding ourselves here that agrobiodiversity isn’t just crops and livestock and their wild relatives — it’s also pests and pathogens and weeds and pollinators and earthworms and brewer’s yeast. It’s one of our leitmotifs. Another is that agricultural and “wild” biodiversity interact. Here’s a paper that kind of brings these two leitmotifs together, into a sort of counterpoint, if I may be allowed to push the metaphor ((C.M. Malmstrom et al. (2007) Barley yellow dwarf viruses (BYDVs) preserved in herbarium specimens illuminate historical disease ecology of invasive and native grasses. Journal of Ecology (OnlineEarly Articles). doi:10.1111/j.1365-2745.2007.01307.x)).

Carolyn Malmstrom and her team at Michigan State University isolated RNA of barley and cereal yellow dwarf viruses from old herbarium specimens of Californian grasses, dating back to 1917. They used such historical samples to trace the history of these agriculturally important viruses back through time, building up a sort of family tree. The analysis suggests that the viruses were present in the Californian native flora in the 18th and 19th centuries, when invasive Eurasian annual grasses (some of them weedy crop relatives) displaced native perennial grasses. In fact, they may have facilitated this invasion by helping the exotic grasses outcompete the natives ((“Non-native invaders amplify spring aphid populations and increase BYDV infection in natives, which in turn suffer substantially reduced survivorship when infected.”)).

The team also found “potential correspondence in the timing of virus diversification events and the beginning of extensive human exchange between the Old and New Worlds.” Humans may have caused the branching of the family tree of some viruses by moving them and their hosts around the world.

Here’s Malmstrom on the significance of her work:

This work points out that the virus world does have an active, long-term role in nature, not just in agriculture… We very much need to understand how viruses can move and influence our crops. If we care about our crops, we need to care about what’s happening in nature.

So: aphids, viruses, native grasses, exotic weedy invaders, crops. Quite a fugue.

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Seeds are not enough

An article in the NY Times tells a frustrating tale of agrobiodiversity use: stunning use by researchers, followed by disappointing use by farmers. It’s the story of Nerica ((The piece has been picked up elsewhere. The Economist’s Free Exchange blog also comments on it.)) — New Rice for Africa. This is a family of varieties derived in the 90s from a biotechnological breakthrough, the hybridization of African and Asian rice. ((Don’t get me wrong, these are not transgenics, though molecular methods were used to overcome the huge challenge of interspecific hybridization.)) Combining “the toughness of O. glaberrima with the productivity of O. sativa,” Nerica varieties have:

– Higher yields (by 50% without fertilizer, and 200% with).
– Earlier maturity (by 30-50 days).
– Resistance to local stresses.
– Higher protein content (by 2%).

A great example of researchers really unleashing the potential of genetic diversity. And one that has been rightly widely recognized. So why have the resulting varieties “spread to only a tiny fraction of the land in West Africa where they could help millions of farming families escape poverty”? It hasn’t been for want of trying:

To quickly move the NERICA technology into farmers’ hands, WARDA and its partners have adopted farmer-participatory approaches, such as the Participatory Varietal Selection (PVS) and community-based seed production systems (CBSS).

The NY Times piece suggests that the reason for Nerica’s disappointing use by farmers comes down to infrastructure. The seeds — even information about them — are not getting to the farmers that need them, and the harvest finds it hard to get to market. That’s because there are few seed companies, roads are bad, telecommunications poor, credit not available. The article also suggests that yield of Nerica has been known to decrease over time “because the new seed was not pure.”

It is undeniable that seed systems could be strengthened in Africa, and that doing so would improve the lot of smallholders. But I don’t know. Farmers are not stupid. They know how to select material for next year’s sowing, and they exchange seeds all the time, often over large distances. Their lives depend on it. Is there something else holding Nerica back? Or maybe it’s just too soon to be expecting miracles of adoption?