Our friend Jacob’s Google-fu is stronger than mine. He found this annotated graph of maize yields in the US.
See how they’ve claimed that blight reduced yields by 18% in 1970? That would be the Southern Corn Leaf Blight that wasn’t a problem, and the yield loss wasn’t caused by lack of genetic diversity.
Well, of course, the government would say that, wouldn’t they, after shelling out all that money on plant breeding and stuff …
Jeremy: I am skating on thin ice here but is it not possible to have genetic uniformity (all plants of the crop genetically the same) but with horizontal, rather than vertical resistance? This would reduce losses compared to the SCLB outbreak, where there was [??] a breakdown of vertical resistance. Also, for broad-spectrum problems genetic variation may be useless. Desert locusts and leaf-cutter ants can take out most species (with exceptions of species with latex). Phytophthora cinnamomi is causing major problems in species-rich Australian forests with no apparent resistance whatever in many wild tree species: major genetic/taxonomic diversity is no use. Any plant pathologists out there?