Category: Wild relatives

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Wheat disease genes

Fusarium graminearum is the fungus that causes Fusarium head blight, a serious disease of wheat and barley. FHB infects the flowers and makes itself at home in the seed, which ends up shrunken and white and loaded with toxins that can have a harmful effect on people and animals that eat the grain. A study just published in Science decoded the DNA sequence of the fungus and sheds some light on its virulence and variability ((The Fusarium graminearum Genome Reveals a Link Between Localized Polymorphism and Pathogen Specialization. Science: 317:1400 – 1402 DOI: 10.1126/science.1143708)).

The sequence of one strain is interesting enough, but the surprises emerged when the researchers, led by Corby Kistler at the University of Minnesota, compared two different strains. There were more than 10,000 differences between the two sequences. Those differences, however, were not spread evenly along the DNA; more than half of the differences were concentrated in just one eighth of the sequence.

So some regions of the genome are much less stable than others. And what genes are in those regions? Mostly ones concerned with infection and virulence, among them the genes for compounds that dissolve the host cell walls and others that digest host molecules so that the fungus can make use of them.

Just why the variability in Fusarium graminearum is concentrated in some areas of the DNA is not yet clear. These areas seem to be hotspots for recombination, which shuffles the DNA during sexual reproduction and so promotes diversity, but this particular fungus doesn’t go in for sexual reproduction all that often. A mystery, then, but one that may still yield new approaches to breeding resistant wheat and barley and perhaps to new kinds of treatment.

You may remember that a joint team of Israeli and US researchers recently reported that a wild relative of wheat, Sharon Goatgrass (Aegilops sharonensis), is loaded with resistance genes that protect it against seven of the most important fungal diseases of wheat. Alas, none of the samples tested was resistant to Fusarium head blight. How about some other wild relative species, though? We shall see.

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Pigs didn’t fly, walked to Europe

We know that agriculture began in the Fertile Crescent about 12,000 years ago and then spread across Europe between 9,000 and 6,000 years ago. But what exactly was it that spread? Was it the idea of agriculture or agriculturalists themselves? Just-published work on the DNA of modern and ancient pigs says it was probably a bit of both. It seems that Middle Eastern farmers migrated into Europe carrying their agrobiodiversity with them — crops and domesticated animals. But, as far as the pig was concerned anyway, they soon adopted a locally domesticated version in preference to the Middle Eastern type they had brought along.

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The services of agricultural biodiversity

The latest (number 18) Biodiversity and Society Bulletin of the Poverty and Conservation Learning Group discusses a new UNEP-WCMC publication ((Ash, N. and Jenkins, M. (2007). Biodiversity and Poverty Reduction: The Importance of Ecosystem Services. United Nations Environment Programme-World Conservation Monitoring Centre, Cambridge.)) entitled “Biodiversity and Poverty Reduction: The Importance of Ecosystem Services.”

It’s a very good assessment of the services provided by biodiversity, in particular to the poor. These services include:

  1. fresh water quality
  2. protection from natural hazards
  3. regulation of infectious diseases
  4. regulation of climate and air quality
  5. waste processing and detoxification
  6. nutrient cycling
  7. medicines
  8. timber, fibres and fuel
  9. cultural services

But food provision and food security are right up front, and that discussion doesn’t just deal with species diversity in farming systems (although this is somewhat underplayed, I think), landraces (though not, unfortunately, wild crop relatives, to any great extent) and wild foods. It also ranges over the wider agricultural biodiversity which supports food production. That means soil micro-organisms, pollinators and the natural enemies of pests:

Although some or all these functions can in theory be replaced by artificial, technologically-derived substitutes, these are often expensive and increase the dependency of poor people on industries and producers beyond their control.

The document ends with some implications for policy. I guess this is the bottom line:

The medium and long-term interests of the poor are likely to be best served by the maintenance of a diverse resource base at the landscape (i.e. accessible) scale, at the very least as a vital risk mitigation measure. This does not, of course, mean that all forms of intensification and adoption of new technologies should be avoided – far from it. Judicious application of new technologies and techniques, use of improved varieties (not necessarily excluding those developed with gene transfer technologies) in agriculture, and appropriate levels of inputs such as nitrogen and phosphate-based fertiliser, can increase productivity and help towards eliminating poverty. Increasing the efficiency of use of existing agricultural lands can actually reduce environmental degradation by reducing the incentive to convert marginal lands. The key is that such development should not be at the expense of the existing natural resource base and should be planned to ensure delivery of medium and long-term benefits, rather than maximising short-term gains.

Pity that the International Treaty on Plant Genetic Resources for Food and Agriculture is not mentioned in the section on international obligations, though.

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I say kumato

The FreshPlaza piece on the kumato is not very long. But it does manage to squeeze in a lot of interesting information. The kumato is a tomato that ripens from green to dark brown. It is the result of a conventional breeding programme which involved a wild species. And it is just coming up to its first harvest in Australia. This definitely deserved more investigation.

There’s no doubt it looks pretty extraordinary. But the most intriguing thing about the kumato is that the wild species involved in its development may be from the Galapagos.

Now, Lycopersicon cheesmaniae from the Galapagos Islands has been used to breed dark orange tomatoes before, though it does not have a dark brown skin like the kumato. ((This species was actually published as L. cheesmanii, after Evelyn Cheesman, but that was incorrect, as the Latinists among us will know, as Ms Cheesman was a woman and the specific epithet therefore requires a feminine ending.)) Check out this excerpt from an article celebrating the late great tomato geneticist and explorer Prof. Charles M. Rick in 1997, five years before his death:

Rick’s research led him on 15 genetic scavenger hunts to Andean South America, the homeland of the tomato, where he hunted for wild tomato varieties carrying useful genes. Among his discoveries were wild tomatoes growing near the tidelands of the Galapagos Islands, despite salty sprays that would have stunted or killed a domestic tomato plant.

Or again:

An excellent lecturer, Rick was much sought after by universities who valued both his rigorous science and his humor and flair for storytelling. A perennial favorite involved his frustrations in trying to germinate wild tomato seeds collected from the Galapagos Islands. The emerging mystery of how the plants reproduce in the wild was only resolved after the seeds were “processed” by passing through the digestive track of a Galapagos tortoise, resulting in vigorous seedlings.

The kumato should actually be the Kumato©. It was bred by Syngenta, and first released in the UK in about 2004, I think. But the Roguelands Heirloom Vegetable Seeds Company also has 40 different dark brown to black-skinned varieties in its collection, and says black tomato varieties first appeared in the 19th century in Ukraine.