Global Crop Diversity Trust

A Foundation for Food Security

A clockwork orange: apocalypse not yet

Californians flipping through the news over their organic, high-fibre muesli must have spluttered orange juice all over their shiny new iPad3s. Huanglongbing has come to their state. This nasty disease -- also known as citrus greening -- has already done a number on plantations of oranges, lemons, limes, grapefruits and more exotic fruits of that ilk in China and Brazil. Since 2005, when it arrived in Florida, it has cost that state over $3.5 billion and 6000 jobs due to the hit on production. That was bad enough for the US juice industry, but California is the source for the bulk of fresh citrus for the table. There’s no known cure for citrus greening, which makes its arrival in Los Angeles a serious threat to the state’s economy.

No cure, and no known resistant varieties -- yet. But that doesn’t mean that nothing can be done, and in fact much has been done. The US Department of Agriculture has a Save Our Citrus campaign going, complete with an app for all those Californian iPads and constantly chirping smartphones that allows citizen scientists to report trees that look a tad off colour. But it is not just commercial orange groves in the Central Valley and trees in suburban gardens that are at risk. California is also home to the US citrus germplasm collection, at the University of California, Riverside. Fortunately, multiple insect-proof screens were installed years back to protect the greenhouses in which the collection is kept. That should keep out the insect that spreads the pathogen, at least for now.

But probably not forever. So researchers have been looking at alternative ways of conserving citrus diversity, as they have for many other crops. In particular, it should now be possible to provide a security back-up for the current field and glasshouse collections by keeping shoot tips at ultra-low temperatures, in liquid nitrogen. That has the added advantage of getting rid of any greening bacteria that have taken up residence in the shoots, a process known as cryo-therapy. As a result, growers can be provided with certifiably clean planting material, a key component of any strategy to contain greening. There has also been some discussion about duplicating at least some of the Riverside material in Costa Rica, in the genebank of the regional training and research centre known as CATIE. CATIE has received support from the Trust over the past few years to regenerate its important fruit collections, including those of citrus. Last year the efforts of the genebank were recognized with an award from a Costa Rican business magazine.

All these are examples of the kind of foresight that genebanks all over the world have to display on a daily basis, in the face of continual, varied threats. Not just from disease, but also from natural disaster, civil strife, and cuts in the power supply. That’s why genebanks need secure, long-term funding. Unless of course the world can do without orange juice on its breakfast tables.

Luigi Guarino
Chief Scientist