http://insciences.org/article.php?article_id=1940
The yellow dragon shows its claws
Published on 3 February 2009, 02:51 by Insciences
Citrus greening, a disease that devastates both orchards and the citrus-growing economy, recently reached Louisiana and California, and the State of Paraná in Brazil. Florida is on the warpath. CIRAD has just had a project accepted under an invitation to tender from the Florida Citrus Production Research Advisory Council.
The yellow dragon, the original name of this disease, originally from China, which is also called greening or, more recently, huanglongbing, is currently breathing fire over all the main citrus production basins worldwide. All the research organizations working on citrus fruits have been called up.
This is a major threat, given the economic consequences and the current lack of any form of cure. The two bacterial forms that cause greening,
Candidatus liberibacter asiaticum and
C. l. africanum, attack the phloem and cause the trees to wilt, reducing their yields and lifespan. The fruits are deformed and smaller than usual, and are thus rapidly unsaleable. To give an example, in countries where the bacteriosis is endemic, primarily in Asia, productivity falls sharply five to eight years after planting and the fruits no longer satisfy commercial standards.
Orange and mandarin trees are particularly susceptible. The list of affected countries continued to grow in 2007 and 2008. The bacteriosis spread beyond its area of origin in Asia some considerable time ago, and is now attacking the American flagships of global citrus growing. After Brazil in 2004 and Florida in 2005, respectively the first and second most important production zones in the world, it was the "little orchard" of Louisiana that was infected in 2008 by the Asian form of the disease, considered to be the most virulent. The alarm was also raised in the summer of 2008 in California, where the psyllid, a type of sucking insect that carries the disease, was discovered. It followed a similar warning from Argentinian producers in the major export zones in the Northeast of the country, where the psyllid is now present, while the disease has been detected across the border, in the state of Paraná, Brazil.
Map of the spread of citrus greening
Mediterranean producers, who have been spared by the disease until now, need to remain vigilant. Trioza erytreae, a psyllid that can transmit the African form of greening, was detected in Madeira in 1994. It has also long been found in the Horn of Africa, Yemen and Saudi Arabia.
What is needed are disease-resistant varieties and effective curative methods. A budget of 20 million dollars was recently released by producers and the authorities in Florida. CIRAD has just been granted project funding under an invitation to tender from the Florida Citrus Production Research Advisory Council (FCPRAC), under its Florida Citrus Advanced Technology Program. The project concerns the in vitro culture of the bacterium assumed to be the etiological agent of greening. The idea is to prove its pathogenicity based on Koch's postulates, and to gain a clearer understanding of its interactions with its vector insect so as to modify the vector capacity of vector populations by transgenesis.
This article is largely based on a text by Eric Imbert, published in the journal FruiTrop, No. 161, November-December 2008, centring on a report on citrus fruits.
FruiTrop is a monthly journal containing news about trade flows of fresh and processed tropical fruits, fresh citrus, and counter-season fruits. Aimed at a readership of economic and political decision makers in these sectors, it is published in French and English editions. 
