Shots for Pierce's Disease

COSMOS

Feature - online

Shots for wine

20 June 2011

by Erick Falcón

Reducing wine merchants to ripping their own crops out of the ground in desperation, Pierce's disease had the potential to leave vineyards devastated. Erick Falcón investigates the effort behind vaccinating vineyards.

ON A NORMAL SUN-soaked summer afternoon in Baja California's Valle de Guadalupe, temperatures average more than 25 degrees Celsius at the shade.

Rain is scarce during the first half of the year, and June couldn't be worse. Only 3 mm recorded this month, so far.

This is Mexico's Mediterranean, at least climatologically speaking. Although better known for its tequila, winemaking in Mexico has picked up signigicantly, and this region is now producing more than 90% of all Mexican wine. A small, but pleasant surprise for connoisseurs worldwide.

Water is a commodity here. Vintners in the region used to joke that 'you have to punish grapes a little to get the best out of them'. But a looming threat was about to take this old gag a little too far: Pierce's disease appeared in 1995.

People started noticing vineyards were drying out. Leaves would turn a yellow-brownish colour, grape production dropped and in some cases, the whole vine died.

When it comes to gardening, just blame it on the neighbour, they say. Political correctness aside, Baja winemakers knew the problem did come from up north.

Between 1999 and 2001, Pierce's disease had wiped out one third of California's Temecula Valley vineyards. With that in mind, some ranchers even took desperate measures by tearing out entire lots of infected vineyards.

IN A MEETING WITH local winemakers in 2006, José Luis Stephano, a biotech researcher at the Autonomous University of Baja California, a publicly funded regional university, learned that the disease could cause heavy damage to the thriving wine industry.

He was then working with a technique called phage display, known for its application in new drug and vaccine applications, so it didn't take too long before he had something in mind to help.

"By the time I was driving back to my lab, I felt I could put my research and infrastructure to use. It's been five years, I believe, and now we can say we have found a few answers to the problem," says Stephano.

Aided by a group of student researchers, Stephano developed a new vaccine that could effectively protect grape vineyards from Pierce's disease, an insect-transmitted illness which has severely crippled important wine regions worldwide for over a century.

The vaccine, based on genetically enhanced bacteriophages, has been shown to effectively kill harmful strains of Xyllela fastidiosa, an insect-transmitted bacterium that has caused millions of dollars in losses to U.S. vintners and wineries all over the American continent. Athough still undetected in Australia, the Australian government has heavily quarantined U.S. grapes since 2001 for fear of importing the disease.

Pierce's disease was discovered in 1892 on vineyards close to Anaheim, California, and since then it has been detected all across the United States, Venezuela, México, Costa Rica and many 'hot spots' across South America, yet it was not quite understood until researchers began linking the illness with insect transmission.

The bacteria that cause the disease, X. fastidiosa, live in the xylem, the water conduction system of plants. When bacteria numbers grow, the xylem becomes blocked, causing water stress, diminished productivity and plant death within one to five years.

THE BACTERIA IS transmitted through insect digestive systems, and the most common carriers are known to be several varieties of the sharpshooter (Cicadellidae) and spittlebug (Cercopidae).

Last year, vineyard losses related to Pierce's disease in Baja's Valle de Guadalupe wine region were tallied by the thousands: 258,000 plants in 86 hectares, a loss of 7% of production, which cost the equivalent of over half a million Australian dollars to replace.

From 1994 to 2001, when pesticide spraying had not yet started, Napa and Sonoma County growers in California lost over U.S.$30 million in income. Losses have reduced since spraying, yet 15 counties in that state remain infested by the sharpshooter bug.

Although it has not reached Australia, this region's favourable climatic conditions, widespread host plants and native insects that can be potential vectors of X. fastidiosa favour a high risk of a Pierce's disease epidemic, according to Peter Merriman, from the Victoria's Department of Natural Resources and Environment.

An hypothetical outbreak in Barossa Valley would cost more than A$10 million dollars by spraying all vineyards, putting the properties in quarantine for five years, which would cause economic losses within $110-135 million, according to a study by the Centre for Policy Studies at Monash University in Melbourne.

Using nanobiotechnology techniques based on lytic peptides from other insects and modified bacteria viruses, commonly known as phages, in Baja, Stephano and his team have developed a vaccine that has effectively shown to kill harmful strains of the Xyllela bacteria, before and after plant infection, and with an improved environmental footprint compared to other pesticides.

"OUR VACCINE specifically targets Xyllela with no harm to other potentially benign bacteria, and is completely biodegradable. At 3.6x105 phages per cell, it completely kills X. fastidiosa in around six to 24 hours in vitro, with no residual effects," says Stephano.

The team began experimenting with bacteriophages - viruses that can infect bacteria - as potential antibacterial agents back in 2006. Researchers injected inert Xyllela bacteria in live chickens in order to obtain fragments of single chain fragment variable (ScFv) chicken antibody genes, from which they select phages that would specifically recognise Xyllela.

Once the genetic library was ready, the team then created an artificial phage by incorporating short protein sequences from insects, known as cecropin P1 lytic peptides (cP1), which become natural defence molecules and are highly active against gram-negative and some gram-positive bacteria.

The ScFv antibody helps the vaccine molecule grapple on to the Xyllela bacteria, while the cP1 peptide has proven successful against various types of X. fastidiosa, including those found in Napa Valley, Bakersfield and Baja, and has several advantages against alternative methods of fighting the bacteria using antibiotics and pesticides.

Stephano says the vaccine his team has developed kills all Xyllela bacteria, whatever the insect carrier of the bacteria, so there is no need to spray with pesticides. In 18 greenhouse-centred experiments, the vaccine was able to eliminate X. fastidiosa with 100% accuracy rates achieved between 24 to 150 hours after the inoculation, although it started to work as early as four hours, according to the researchers.

So far, lab testing and greenhouse experiments show that the vaccine successfully inoculates many kinds of vineyards; red globe, Pinot Noir, Cabernet Sauvignon and Merlot vaccination results have proven the same result. Xyllela is gone, with a high long-term survival rate.

"We still don't know the length of the vaccine's immunity time span. But I can tell you that after one year and a half, Pierce's disease has not reappeared into our samples," Stephano says.

The research team is currently evaluating the results of outdoor field testing held in a large-scale Baja winery's vineyards, but Stephano plans to expand the scope of his work "to build an integrated system with phages included, which will result in permanent plant immunity".

And that's something to drink to.