Monday, December 02, 2002

While I was away: 1. human acquisition of resistant bacteria from turkey [Forbes]; 2. caviar's imminent demise [BBC]; 3. the EU finally agreed to GM labelling rules [Reuters] as the US prepares for another trade war [BBC], and the Illinois Farm Board worries about its export market; 4. potato blight returns [Science]:
One problem, says Harold Platt, a plant pathologist at the University of Prince Edward Island and the Agriculture and Agri-Food Canada Research Centre, is near-total dependence on fungicides, which are losing their effectiveness as resistant strains spread. "A hundred and fifty years of relying on a single management tool has been to our detriment," he says. Another problem is that the United States and Canada, in particular, have come to rely on just a few vulnerable potato cultivars--most prominently, the versatile Russet Burbank, great for baking and the mother of most fast-food French fries, and good "chippers," such as Ranger. "As potato diversity shrinks and Phytophthora strains multiply," says Platt, "entire crops are at risk of being wiped out."....

Although travelers carried the potato (Solanum tuberosum) from the Americas back to Europe as early as the 1500s, the disease seems not to have made the trip until the 1840s. Initially, when P. infestans did appear in Europe, it was unstoppable. It was only thanks to the discovery of the organism in the 1860s--and fungicides to fight it--that the Irish disaster wasn't more common. In countries that have been able to afford fungicides, frequent applications during the growing season--although imperfect, expensive, and hardly environment friendly--have held the disease at bay. But even that is changing.

No fungicide has ever been found to which P. infestans could not ultimately adjust. Metalaxyl, for years the most commonly used, appeared increasingly impotent starting in the 1990s. And it was never effective against established infection. Cultivated potato varieties that in the past showed a measure of resistance to late blight, moreover, succumb readily to newer strains. Indeed, no potato has ever been developed with defenses that Phytophthora could not ultimately breach. And the attacker's arsenal is growing more elaborate.

Until recently, most infections outside Mexico were caused by a single type of P. infestans (A-1), which reproduces asexually and can survive only in the potato's tissues. Infected tubers used for seed, left in cull piles, or unharvested in the ground have been the sources of spores from one growing season to the next. But starting in the late 1980s, a second mating type, or "sex" (A-2), previously limited to the Toluca Valley, escaped from Mexico, allowing sexual reproduction with A-1 in new areas.

Individually, A-1 and A-2 produce sporangia, reproductive bodies that are short lived and require a moist environment. But when A-1 and A-2 are introduced to each other, they mate to form multitudes of thick-walled oospores that can persist independent of the host plant--in soil and during drought, for example. Sexual recombination also allows the organism to adapt more readily to adverse conditions.

The consequences are already apparent. In the past, most Phytophthora races in North America had one, two, or at most three virulence genes; in Western Europe they had no more than four or five. In recent tests around St. Petersburg, 80% of the Phytophthora races had six or more such genes. Some had as many as 10. In addition, in the 1990s, especially aggressive and fungicide- resistant strains of the simple A-1 type started to appear.

For most countries, fungicides have never been an option. And the new fungicide- resistant races of P. infestans have upset the balance of power even in rich countries. Everywhere, in short, it's assumed that the most promising and sustainable solutions will involve not new fungicides but genomics: genetic manipulation aimed at deactivating the organism or engineering potatoes that have "durable resistance," lasting 10 years or more. Although the genomics projects are young, they are making progress.

5. David Schubert was criticized for suggesting that GM food be tested for safety, and responded in Nature Biotechnology:
It is indeed a fortunate facet of science that the quantitative aspect of authorship does not dictate the validity of the conclusions! The impetus for my commentary was my repeated laboratory observation that the slightest genetic modification of a cell leads to completely unpredicted phenotypes. A careful reading of the plant literature supported my conclusions from animal cells. The commentary intended to raise this concern in the context of generating further impetus for labeling and stringent testing of GM food. I had no a priori commitment to a particular technology, no pre-existing political ideology, and I did not deliberately ignore any pertinent published material. I do believe, however, that both replies suffer from these problems. They make claims about technology and safety-testing requirements that do not exist, use my statements out of context, and are rather adroit at the use of tenses to skirt questions regarding testing.
The whole world is becoming a simulacrum of Fox News.


Post a Comment

Links to this post:

Create a Link

<< Home

©2002-2005 by the author