Late blight is forever

by Jeremy Cherfas on March 19, 2012

Dave Allan, writing in The Herald, a Scottish paper, almost a month ago, sang the praises of some very blight-resistant potatoes called the Sarpo group. I picked up the story because these varieties were first bred 40 years ago in Hungary by crossing local Soviet varieties with wild relatives collected by Nikolay Vavilov in South America. I stuck it on the back boiler, meaning to write something up for St Patrick’s day last Saturday.1

Meanwhile, there’s been a bit of a todo lately over field tests of GM potatoes in Ireland and England. According to The Sainsbury Laboratory’s FAQ, the potatoes have been engineered to increase their resistance to late blight, using genes from wild potato species. I think the same is true of the Irish trials, which is part of Amiga, an EU research project.2

There’ve been all sorts of responses to this news, much of it utterly predictable. People thought it “ironic” that Ireland should question the need for blight-resistant potatoes, presumably in view of the famine of the 1840s. Others questioned the need for engineering blight resistance, given that there are some extremely resistant varieties.

But few people have questioned the basic premise: that engineered blight resistance will be more durable than that achieved by conventional breeding. I’m not sure there’s evidence for this either way. In any case, I wouldn’t expect it, a priori.

The point is quite simple: overcoming resistance is what pests and diseases do. They multiply like mad, and every new individual is a new lottery ticket. Sure, the odds of a jackpot are slim. But in every case I know of, the question is not if but when.

That was my response when NPR reported last week that, according to Monsanto scientists, “considering how hard it had been to create those crops, ‘the thinking was, it would be really difficult for weeds to become tolerant’ to Roundup”. Regardless of how easy a ride reporter Dan Charles gave Monsanto, this is just daft. Natural selection has the numbers and the time to overcome anything mere researchers can come up with.

Potatoes are susceptible to late blight, and get sprayed a lot. A new variant of the blight pathogen, known as ‘superblight’ or Blue 13, destroys even the most resistant of previously resistant varieties but not Sarpo varieties. Sarpo Mira has five different resistance genes; is that enough to protect it forever from anything late blight can throw at it? No.

The Sainsbury Lab says the main reason to engineer blight resistance is because breeding is difficult; easier to insert the genes into an already desirable variety. The Savari Research Trust says Sarpo varieties are very tasty. Both laboratories, and everyone else, regardless of whether they engineer blight resistance or select for it, will have to stay in the game for as long as blight is around. Forever.

Finally, shifting back to Ireland and the famine; just how many engineered varieties (if any) are going to be deployed? Leaving aside the historical, economic and colonialist explanations for the devastation wrought by late blight in 1845, the proximate cause was the prevalence of a single potato variety, Lumpers, that was susceptible.

The danger of too little diversity remains, regardless of the crop, regardless of the source of resistance.

  1. Couldn’t manage that; Monday is probably better anyway. []
  2. Assessing and Monitoring the Impacts of Genetically modified plants (GMPs) on Agro-ecosystems, which proves, once again, that the secret to EU funding is a good acronym. []

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