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Wednesday, July 22, 2015

Olives at Risk

A very old olive orchard I visited in the hills on the Greek island of Corfu
(originally posted on Forbes, 7/21/15)

This spring my family traveled in Italy and Greece where I became enchanted with their ubiquitous olive groves.  Many are on steep hillsides and some of the trees are extremely old with beautifully gnarled trunks.  I began to think I should try to grow an olive tree at home in the San Diego area.  Then I learned some sad news about olives – news that suggests that it will become a more scarce luxury food in the future.

Although olives are an ancient crop, expanding their supply to keep up with population growth has been difficult. If we compare the production of crops in the early 1960s with that 50 years later (2005-10) almost all have increased in total tonnage, but much of that increase has come through improved yields and not just more extensive planting (see table below).  (Table)

How the supply of some vegetable oils has changed over 50 years

Olives stand out among food oils in that all the increased supply has come from additional planting.  Global average yields are 20% lower than they were 50 years earlier. No wonder olive oil is expensive.

But now, olives in those picturesque groves in Southern Europe are threatened by a deadly disease.  It is apparently a new strain of a North American organism called Xylella fastidiosa. Strains of that pathogen cause diseases of various crops, but it is not known to affect olives in California. Somehow a new, olive-infecting strain of Xylella originated in Central America and traveled to Europe via an ornamental plant.  In Italy, the pathogen is being spread by the common spittle bug and is now killing trees in dramatic fashion.
Olives trees killed by Xylella. Image from Institute of Plant Virology Italy.
Thus olives in Italy join citrus in Florida and grapes in California as examples of crops in jeopardy because of the inadvertent, global movement of bacterial pathogens or the insects that vector them.  The grape infecting strain of Xylella was only a relatively minor issue for California grapes until a new insect vector, the Glassy Winged Sharpshooter, was transported into the state – again probably on an ornamental plant.  The disease thatis killing off Florida citrus, and threatening citrus from Texas to California, arrived on an ornamental plant from Asia with both the vector and the pathogen (do we see a trend here about the movement of exotic ornamental plants?).

Problems caused by moving plant pests around the world is nothing new.  The three-century delay in the arrival of the potato late blight pathogen allowed that New World crop to become a staple, only to be decimated leading to the Irish PotatoFamine of the 1800s.  Two pests spread from North American grape species nearly destroyed the European wine industry in the late 1800s.  It is said that the movement of coffee leaf rust from Africa to Java in the 1870s was the reason that the English had to switch to tea.  However now, with ever increasing global travel and trade, many more crops are at risk. 

Although it would not be a quick solution, genetic engineering might be a good option for the olive problem as it would be for citrus, grapes, potatoes and coffee.  Whether that will ever happen is, unfortunately, another question.  Apparently the 2015 olive crop inCalifornia is looking good.  Perhaps that will take some pressure off our demand for olive oil from Italy.  In any case, we should enjoy the luxury of olives before they become even less available.

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