Category: Genetic diversity

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Upstream blast

ResearchBlogging.org Blast is one of the worst rice diseases. I believe that, thanks to the breeders, most modern varieties have decent levels of resistance. After all, they can be used in varietal mixtures to protect traditional glutinous rice varieties from blast. 1 Unfortunately, much of this resistance is not durable, because the pathogen overcomes it with time.

For a long time, durable resistance has been known to exist in some Japanese varieties. But these varieties have not been useful for resistance breeding, as the resistant parent also brought along undesired characteristics: the offspring always had poor eating quality.

Shuichi Fukuoka and colleagues have found out why. They report in Science 2 that it is because of a tight genetic linkage. Resistance is conferred by the Pi21 locus, and:

The eating quality of plants carrying the elite cultivar’s chromosomal sequence from a point less than 2.4 kb downstream of the Pi21 locus was equivalent to that of the elite cultivar, and the plants showed a high level of blast resistance. In contrast, plants carrying the donor chromosomal sequence up to 37 kb downstream of the Pi21 locus showed inferior eating quality.

By crossing in just the right bit of the chromosome, and making sure that the neighboring areas do not tag along, resistance can now be transferred, without spoiling the taste.

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Wild cassava genetics used to document past changes in vegetation

ResearchBlogging.orgWas southern French Guiana always forested, a refugium for forest species, or was it dominated by more open vegetation during drier, glacial times? A recent paper in Molecular Ecology tries to decide between these competing hypothesis, and the interesting thing for us at the Agricultural Biodiversity Weblog is that it does so through a genetic study of a crop wild relative. 3

Manihot esculenta ssp. flabellifolia is the closest wild relative of cassava. It is “distributed on an arc partly encircling the Amazon basin, from eastern Bolivia and Peru eastward to northeastern Brazil, northward to the Guianas and then westward to Venezuela.” Its habitat is the transition zone between forest and cerrado in the south, and open environments such as savannas and rocky outcrops in the north. In French Guiana, which was the focus of the study, it is found both in the coastal strip, and on isolated granitic outcrops (inselbergs) in the forested south, with a large gap in between.

Seven microsatellite loci were used to investigate the genetic relationships among 14 populations, 4 from inselbergs and the rest from the coast. The results are pretty easily summarized. First, the inselberg populations were very similar to each other. Second, they were quite different as a group from the coastal populations. Finally, the coastal populations were highly differentiated among themselves.

So, what do these results tell us about the past vegetation history of the region? One conclusion was that the coastal populations (which incidentally, in contrast to the inselberg populations, showed some evidence of introgression from the crop) are relatively recent, and arrived from savannas to the west through a series of bottlenecks, rather than from the south. As for the southern inselberg populations, given the limited range of pollen and seed flow, they seem to be the remnants of a formerly more extensive, fairly homogeneous population. 4 That suggests that southern French Guiana was drier and had a more open vegetation before the Late Glacial Maximum 10,000 years ago. There was probably a forest refugium in the central part of the country, but not in the south.

Assuming, of course, that the adaptation of the species hasn’t changed much along the way. It remains to be seen whether the same pattern will be found in other taxa. Perhaps other species of agrobiodiversity interest will be investigated in the same way.

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Anthropologists and geneticists see the origin of agriculture in different ways

Dorian Fuller has answered Paul Gepts’ comment on Dorian’s post at The Archaeobotanist on the multiple origin of agriculture, which I originally blogged about a few days ago. Let’s remind ourselves of the argument.

This was Dorian’s parting statement on the original post:

…agriculture, like modern human behaviour, was not a one time great invention, but the product of social and environmental circumstances to which human groups with the same cognitive potential responded in parallel ways.

Paul Gepts countered with this:

As a geneticist, I am somewhat surprised that the issue of parallel inventions of agriculture is still an issue… biochemical and molecular data also show distinct, and likely, independent domestication in different geographical areas, not among only among different crops, but also within a crop gene pool.

And now Dorian again:

My sense is that most of the genetics community has shifted towards seeing multiple areas of independent origin, but within archaeology there is still a penchant for reducing historical complexities to as few origins as possible — often focusing on where more archaeological research has taken place rather than considering other forms of evidence (biogeography, genetics) that should encourage us to take up research in the less-explored or unexplored areas.

Read the full exchange.

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