Category: Wild relatives

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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.

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Bottlegourd to the rescue

Zucchini yellow mosaic virus (ZYMV) does not, alas, restrict itself to zucchini, or even courgettes. It attacks most cucurbits, including cucumbers, melons, pumpkins, squash, bottlegourds and watermelons. One of those, however, the bottlegourd Lagenaria siceraria may also hold the antidote to ZYMV. Scientists at the Agricultural Research Service of the USDA grew seeds of 190 different accessions from a USDA genebank and inoculated the seedlings with virus.

To their surprise, 36 accessions of the 190 screened—33 from India alone—were completely resistant to ZYMV infection, and another 64 accessions were partially resistant. They also found that ZYMV resistance is heritable in crosses between different bottlegourd accessions, enabling the development of bottlegourd varieties with enhanced virus resistance.

Breeding resistance from Lagenaria into other cucurbits may be difficult, although if they can isolate the gene(s) responsible other options become possible. And even they may not be needed. Growers can graft watermelons, for example, onto bottlegourd rootstocks and benefit from the resistance that way.

Wl020 p.s. I shouldn’t get snitty, of course, but Wikipedia’s entry on bottlegourd in China is bizarre in the extreme. I’m not going to wonder what a “remedy for health” is, though it sounds to me a lot like a disease. I am going to wonder why there is absolutely no mention of the presence absolutely everywhere of a jillion small bottlegourds as good luck charms. The Buddha used one to carry “life’s essentials”.

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Conserving crop wild relatives

A paper just out in Biological Conservation discusses crop wild relatives (CWR) in the UK. ((Creation and use of a national inventory of crop wild relatives. Biological Conservation. In Press, Corrected Proof. Available online 27 September 2007. Nigel Maxted, Maria Scholten, Rosalind Codd and Brian Ford-Lloyd.)) The authors include some of the same British boffins who wrote a global survey of CWR conservation. The paper describes how to develop a comprehensive national plan for the conservation of CWR, using the UK as an example. Unfortunately, it is behind a paywall, but I’ll summarize the main points.

First, of course, you need to know what you’re dealing with. A UK national inventory of CWR was developed as part of the EU-funded PGR Forum project. It contains 15 families, 413 genera, 1955 species (44 endemic) — that’s 65% of the native flora. So then you have to prioritize. For example, 13 of the UK’s CWR species are considered threatened according to IUCN criteria and one is apparently extinct in the wild ( the grass Bromus interruptus). The authors ran an iterative algorithm on the distribution data for about 250 CWR species ((Chosen because of their potential economic value and perceived threat level.)) to identify the smallest number of areas which would contain the largest number of species. Seventeen 10×10 km grid squares were selected within which could be found two thirds of the priority CWR species.

To what extent are these “hotspots” already protected? Interestingly, none of them “did not overlap with existing UK protected areas.” What’s now needed is to confirm the presence of the target species in the protected areas and come up with management plans specifically aimed at the CWR.