27 April 2011

"Pistachio disaster" reveals the downside of monoculture

The Australian pistachio crop has been ravaged by an epidemic of anthracnose -
According to Nelson, the outbreak isn’t just a function of weather. It’s likely a result of monoculture crop practices, in which just one or a few varieties of a crop are planted. Australia’s pistachios are descended almost entirely from a single cultivar developed in the early 1980s; selected for the nuts’ flavor, aesthetically pleasing color and easy-splitting shells, the variety was an easy choice for farmers — but with that choice, the seeds of an epidemic may have been planted.

“Those are the varieties that are best for them. That’s why we have monocultures: They can’t plant something that isn’t profitable. But monocultures create these problems,” said Michailides.

Monocultures are the rule in modern agriculture, and are especially vulnerable to disease, as a pathogen that can infect one plant will likely be infectious to the rest. That’s happening now in Australia with Tropical Race Four, a fungus that threatens to destroy the country’s banana industry, and may eventually doom modern bananas altogether.

But increased vulnerability isn’t the only problem. Monocultures also function as evolutionary crucibles for pests, exerting selective pressure in a single direction: toward any mutation that helps the pest spread.

That seems to be happening in the resurgence of wheat rusts — the defeat of which decades ago was the Green Revolution’s founding achievement. And that may have happened, at a smaller scale, with the emergence of anthracnose in pistachios.
More at the link.  We and our neighbors became familiar with anthracnose when it spread through our subdivision several years ago in the form of "apple scab" on the beautiful (and popular) crabapple trees.  The leaves developed black lesions and fell early from the tree.  If any of you notice something similar with your apple/crabapple trees, be sure to call an arborist, because although the tree can tolerate partial defoliation, if it happens several years in a row, it can kill the tree. 

Text from Wired Science; photo credit Themis Michailides. 

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