To the standard hymn-sheet of crop failures associated with genetic erosion we can now add an example from livestock. A mutation in a single Holstein bull — Pawnee Farm Arlinda Chief, who happens to father super-productive daughters — also causes spontaneous abortion. The mutation spread through the US dairy industry and caused $420 million in losses.
That’s a crazy number, but here’s an even crazier one: Despite the lethal mutation, using Chief’s sperm instead of an average bull’s still led to $30 billion dollars in increased milk production over the past 35 years.
There’s nothing like that, at least not that I can think of, for crops, but it is just one of the nuggets in a super piece from The Atlantic magazine on selective breeding.
Maybe the ripening mutants in tomato? Increases vine/shelf life but decrease tastiness.
I can see that, but it hasn’t really cost the tomato industry anything. Or has it, in lost sales?
Hard to tell. People might buy less of them if they regularly taste bland. I do.
Another example could be the Texas cytoplasm in maize, which conferred for male sterility that allowed a cheaper way for hybrid production. Which I guess it increased accessibility to the seeds and yield of the farmers. But it is also susceptible to leaf blight.
Jeremy: I’m not sure that crop failures are associated with genetic erosion. Surely crop failure is associated with the loss of the more susceptible varieties or crops, which leaves the more resistant ones to survive and reproduce. Over time less crop diversity is equal to higher resistance. That is a good outcome of `erosion’. At least, that is what crop breeding is aiming for. You could even argue that, for example, the vast diversity of wheat varieties in Ethiopia is a sitting target for crop failure. A new aggressive strain of Yellow Rust (Yr27) has clobbered highly susceptible traditional varieties of wheat. In that case un-eroded diversity was very much a bad thing in allowing the pathogen to thrive. This could have happened with Ug99 – very possibly lurking for decades in one of the vast array of wheats in Ethiopia.
But if all that’s left is susceptible varieties…
Luigi: We could argue that that is what genebanking is all about – protecting susceptible varieties in the cold store from pests and disease in the field. For example, a landrace (maintained in a farmer’s field) with a valuable resistance to pest/disease `A’ may be lost for ever because it is susceptible to pest/disease `B’ that comes along by chance. As only small samples are supplied by genebanks for resistance trials we cannot lose the lot at one go. At CIAT we were doing a routine multiplication of 5000 samples of common bean. One third of them produced no usable seed as a result of massive virus pressure – almost certainly by aphid transmission from one or more bean plants with virus: one of the hazards of varietal diversity that farms suffer from. But we had back-up seed and several locations for multiplication – no disaster.
Another problem is `new encounter’ diseases originating from, for example, wild relatives. There may be no resistance at all in an entire crop. There is still not much field resistance to potato blight, which may have been transferred from wild relatives in Mexico in the 1800s (and little or no resistance even in the vast diversity of potato in Peru, where the blight was a `new encounter’ disease). I have seen whole fields of very valuable seed potatoes destroyed by blight here in northern Scotland. The irony is that northern Scotland is very suitable for seed potato multiplication as aphids are rare and virus transmission manageable.