Category: Wild relatives

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The Cretaceous roots of agriculture

A comment on a long but fascinating post on yeast genetics and evolution at The Loom sent me to a New Scientist article from a couple of years back which is perhaps more immediately relevant to our agricultural biodiversity focus here.

Some time in the distant past Saccharomyces cerevisiae, to give it its full name, developed a chemical trick that would transform human societies. Some anthropologists have argued that the desire for alcohol was what persuaded our ancestors to become farmers and so led to the birth of civilisation.

The article goes on to describe how brewer’s yeast evolved its somewhat surprising abilities. It turns out that its peculiar habit of carrying out anaerobic respiration even in the presence of oxygen — at a steep energetic cost, and resulting in the production of what is usually a poison, alcohol — dates back to an accidental duplication of its genome back in the Cretaceous. Eighty million years ago later, bakers and brewers are daily taking advantage of a genetic mistake that took place in a microscopic fungus when dinosaurs ruled the Earth. Isn’t agrobiodiversity wonderful?

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Can wild relatives survive introgression?

Crops can benefit from the introgression of genes from their wild relatives, but what about the other way around? Is the survival of crop wild relatives jeopardized by the “genetic pollution” caused by hybridization with the cultigen? A paper just out in the Journal of Applied Biology takes an experimental and modeling approach to answering this question ((D. A. P. Hooftman, M. J. De Jong, J. G. B. Oostermejer, H. C. M. Den Nijs. 2007. Modelling the long-term consequences of crop-wild relative hybridization: a case study using four generations of hybrids. Journal of Applied Ecology 44 (5), 1035–1045.)).

The researchers monitored the germination, survival and seed-set of hybrids between wild (Lactuca serriola) and cultivated lettuce (L. sativa). The overall fitness of hybrids was higher than that of the “unpolluted” wild relative in the first couple of generations, but as those hybrids were selfed and backcrossed, their fitness decreased. These data were then entered into a model, to see what would happen over time to a L. serriola population exposed to geneflow from the cultigen. What happens is that the wild relative can indeed be completely displaced by hybrids, but that is not a foregone conclusion, and in any case displacement, if it takes place, will not be as rapid as predicted by previous models which did not take into account the breakdown in heterosis.

So genetic pollution does pose a real threat to crop wild relatives in the field ((The likelihoods of both hybrid occurrence and L. serriola displacement were still at least 60%.)), but perhaps not as great as some have suggested. And in any case we now seem to have a model that can be used to assess the risk of genetic pollution, including by transgenes.

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Another crop wild relative to the rescue

I’ve just run across a new paper which, apart from being interesting, also gives me the opportunity to apologize for nibbling earlier today an item on Fusarium head blight (FHB) that Jeremy had already discussed at some length about a month ago! The original item had to do with the sequencing of the genome of the fungus which causes FHB, a serious disease of wheat and barley. Two strains were in fact compared, and Jeremy blogged about the differences that were found in the two sequences. He ended his ruminations thus:

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.

Well, the Molecular Breeding paper I’ve just been alerted to should make him happy. In it, Xiaorong Shen and Herbert Ohm at Purdue report that they found resistance to FHB in bread wheat lines into which had been introgressed bits of a chromosome of a wild relative, Tall Wheatgrass, or Thinopyrum ponticum. The bits of chromosomes were from different sources, and their introgression into wheat caused different reactions to FHB infection, showing that there’s variation in resistance to the pathogen as well as within the pathogen itself.

GRIN has records for two accessions under this name, both from the Vavilov Institute in Russia, but suggests that name is actually a synonym for Elytrigia pontica, for which there are a total of 18 accessions in the USDA system (another synonym is Triticum ponticum). SINGER has records for two accessions of Elytrigia, but none for the species in question, under none of these synonyms. EURISCO has only one record. Looks as though some more collecting may be in order. The distribution of the species seems to be central and southern Europe, the Caucasus and western Asia.