Science for Brazil (Reino Unido)

Does Brazil hold keys to global “Plant Plague”?

Publicado em 02 janeiro 2018

A sinister plant disease with the power to destroy farmers’ livelihoods named “the Ebola of olive trees”  is on the march across Europe during 2018; yet the same bacteria could for decades have been affecting coffee plantations, orange groves and other high value crops in Latin America.

In fact some of the science now needed to fight the disease in Europe, may already have been completed in Brazil. In Latin America  the focus has been on protecting orange groves and coffee plantations rather than olive groves – but the disease is the same one now affecting Europe.

Xylella fastidosa or olive leaf scorch disease, is described by European media as one of the “most dangerous pathogens worldwide”. In Europe it was first detected in olive trees in Puglia, southern Italy, in October 2013. It has been recorded in a number of other locations, including southern France. The disease is reported to have wiped out entire olive groves. The European Commission has stepped up protections against the spread of X.fastidiosa, which can infect more than 350 different plants.

No one knows for sure, but the new plant plague coming to Europe could represent a repeat of the late 19th century’s economically-devastating phylloxera epidemic. This destroyed most of the vineyards for wine grapes in Europe, most notably in France, finally breaking that country’s monopoly of fine vintages. Phylloxera was introduced to Europe when avid botanists in Victorian England collected specimens of American vines in the 1850s, and sent these by steamship to Europe.

The X. fastidiosa bacterium invades the xylem vessels that a plant uses to transport water, causing it to display symptoms such as scorching and wilting of its foliage, eventually followed by the death of the plant. The economic effect of the disease in Europe – the world’s largest producer of olive oil – is already visible, with a 20% hike in oil prices following an earlier X. fastidiosa outbreak in 2015.

However the disease – which has reached Mallorca in Spain and during 2018 could reach epidemic proportions across the EU’s olive oil-producing agricultural heartland – is no stranger to Brazil, and some of the basic science now needed to contain its spread in Europe may have already been done by researchers in the universities of São Paulo state, Brazil’s agricultural heartland.

This thorough groundwork by Brazilian scientists – including the sequencing of X. fastidiosa’s genetic makeup – which was originally focussed on variants affecting orange groves and coffee plantations – could prove of inestimable value to Europe’s beleaguered olive grove owners.

Together with Fundecitro (an orange growers’ industry association),  FAPESP (the São Paulo state institution for  funding  scientific research) in 2016 held a conference to share the outcomes of   groundbreaking research into X. fastidiosa. The project was named Genoma FAPESP and represented 15 years’  of detailed work in identifying and tracking the disease.

The 2016  conference — opened by FAPESP prersident José  Goldemberg and Lourival Monaco of  Fundecitro – highlighted the work of more than 200 researchers at various  institutions in Brazil and other  countries. As a consequence, Brazil  has begun to implement  radical  changes to the production of  orange tree grafts,  and there have also been  new regulations aimed at stamping out the disease.

In fact what European  news media are presenting as a  “new” disease, was first recorded as far back in 1987 in Brazil and a much-cited  Nature report published in 2000 identified the strains already affecting agriculture in the Americas. The bacterium is related to the well-known pathogen for Pierce’s disease affecting North American grapevines.

“Citrus variegated chlorosis (CVC), which was first recorded in Brazil in 1987, affects all commercial sweet orange varieties. Symptoms include conspicuous variegations on older leaves, with chlorotic areas on the upper side and corresponding light brown lesions, with gum-like material on the lower side. Affected fruits are small, hardened and of no commercial value,” wrote the Nature authors who included Brazilian scientist J. C. Setubal of the University of Campinas, São Paulo state.

Worse, perhaps, is the potential effect of one variant of the disease on Brazil’s principal cash-crop – coffee. In a 2015 paper in Microbiology a group of Brazilian plant scientists led by Luiz R Nunes of the ABC Federal University in São Paulo, identified X. fastidiosa’s role in “coffee leaf scorch (CLS) – a disease with potential to cause severe economic losses to the Brazilian coffee industry.”

The  authors note that “the widespread distribution of X. fastidiosa strains infecting so many important crops, and the economic losses already experienced by both the citrus and wine industries, have made X. fastidiosa a major agronomical concern in the American continent and this micro-organism has been the subject of increasing attention by many research programs since the mid-1990s (Doddapaneni et al., 2006, 2007). As a consequence of these efforts, one X. fastidiosa strain (9a5c), associated with CVC in Brazil, was the first plant bacterium to have its complete genome elucidated.”

Olive groves – a recent introduction and considered a high value option by Brazil’s farmers in São Paulo and Minas Gerais states – are not immune to the variant poof the same disease affecting Europe. A report in Phytopathologia Mediterranea published on January 6, 2016, identified the first reports of olive leaf scorch in Brazil, associated with Xylella fastidiosa subsp. Pauca.

The Microbiology paper describes how the group’s comparative genomic analysis of coffee-infecting Xylella fastidiosa strains isolated from Brazil, showed the genetic structure of the bacterium is highly flexible and subject to mutations that could affect multiple plant types. “A surprisingly large proportion of genes present in the flexible gene pool of X. fastidiosa are shared amongst distantly related strains, indicating the possibility that the bacteria are actively and constantly exchanging genetic material in the wild,” the authors wrote.

Their graphic analysis (see illustration) shows that X. fastidiosa affects coffee, citrus, almond, plum, mulberry, as well as elm, ragweed and Temecula.

The sequencing and analysis in this project were carried out by a network of 34 biology laboratories and one bioinformatics centre. The network is called the Organization for Nucleotide Sequencing and Analysis (ONSA)42, and is entirely located in the state of São Paulo.

The Microbiology authors write: “Before the elucidation of its complete genome sequence, very little was known of the molecular mechanisms of X. fastidiosa pathogenicity. Indeed, this bacterium was probably the least characterized of all organisms that have been fully sequenced. Our complete genetic analysis has determined not only the basic metabolic and replicative characteristics of the bacterium, but also a number of potential pathogenicity mechanisms. Some of these have not previously been postulated to occur in phytopathogens, providing new insights into the generality of these processes. Indeed, the availability of this first complete plant pathogen genome sequence will now allow the initiation of the detailed comparison of animal and plant pathogens at the whole-genome level. In addition, the information contained in the sequence should provide the basis for an accelerated and rational experimental dissection of the interactions between X. fastidiosa and its hosts that might lead to fresh insights into potential approaches to the control of CVC.”

Further work was done by a team led by João Lopez, which in 2008 published a detailed survey in Applied and Environmental Microbiology of both Coffee Leaf Scorch (CLS) and citrus variegated chlorosis (CVC). Once again the lion’s share of the research was executed in Brazil, and funded by both the government research institution CAPES, and the citrus fruit industry.

What’s clear is that the threat to world agriculture posed by X. fastidiosa is both far-reaching and wide-ranging. Its ability to attack a wide variety of economically-valuable plants across broad geographic swathes suggests that plant scientists and bacteriologists around the world need to get together to address this “plant plague” that  could do tens of  billions of  dollars’ worth of damage.

Perhaps Brazil’s plant and bacteria scientists – having already done much of the groundwork – will find now their prescient studies into X. fastidiosa materially affect the progress of this new campaign.