Brazilian researchers have called on the world’s governments and citrus bodies to promote detection schemes for citrus disease ‘Huanglongbing’ (HLB), during a Food and Agricultural Organization (FAO) regional consultation in Santiago, Chile. Silvio Lopes and Renato Bassanezi from Brazil’s Citrus Defense Fund (Fundecitrus)­­­, say small growers need support and education or they will not survive.

The insect Diaphorina citri may only grow as large as 4mm (1.7in) long but by carrying virulent bacteria it has wreaked havoc on citrus crops in the Americas and Asia, while also stretching out as far as Ethiopia and Papua New Guinea.

While official detections of HLB have been recorded in these regions, citrus greening disease could be in more places than is recognized due to long incubation times between plant infection and symptoms.

There are two types of insects that act as vectors for the disease, carrying different strains of bacteria believed to be responsible for citrus greening. Diaphorina citri carry the Liberibacter Americanus and Asiaticus strains, while Trioza erytreae carry the Liberibacter Africanus.

It is the virulent Americanus that caused the Brazilian outbreak in 2004, which has since spread to Central America and the U.S. states of Louisiana, Georgia and South Carolina.

Lopes says the insect has also been found in areas where disease symptoms have not yet been observed, such as Venezuela, Argentina, Bolivia and Oman, as well as the U.S. states of Texas, Arizona, California and Mississippi.

“I think the countries where the Diaphorina citri or Troiza erytreae are already present are the ones I’d guess would have the disease first, and you have lots of countries in this situation,” he says.

Fundecitrus researcher Silvio Lopes

“If you are close to countries where the disease is, even by wind, you imagine tornadoes, or it could be by car, it’s such a tiny insect and it could be carried.

“I believe that the vector and the disease are in more countries, that the number is bigger and higher but the people didn’t look carefully. How can you say ‘the disease is not here’ just by looking at the trees? You can say it was not found, so it’s complicated.”

He says what the industry needs is for governments and media personalities around the world of the ‘Oprah’ ilk to simply show people what the symptoms look like, as the rapidly-spreading disease often starts in backyard gardens.

“If the general public knows about the problem, they could be of help to find the disease at the first moment and once it’s found don’t give up – this is a constant war once the disease is there, there is no resting.

“If you are smart enough you’ll do everything that needs to be done – not spending time in meetings discussing the politics of ‘let’s do that next year’, no. The disease will not stop and wait for the politicians to discuss.

“There is no cure for Huanglongbing, no antibiotic – if it is introduced to an area our management should be to keep that incidence at very low levels or the industry will be in danger.”

The Brazilian experience and outlook

Citrus is big business in Brazil, with 838,360 hectares of orange plantations making it the world’s largest producer of the fruit, recording annual volumes of more than 18 million metric tons (MT).

This represents around a third of the global market but the majority goes towards the production of orange juice. Around 80% of this is concentrated in the state of Sao Paulo, while the states of Paraná, Bahía, Sergipe, Minas Gerais and Rio Grande do Sul also have significant orange farms.

In addition, the South American country produces more than one million MT of mandarins and slightly less than one million MT of Tahitian limes and lemons annually.

But this could all come under threat by HLB if the country doesn’t see a full take-up of control and eradication policies by growers.

Lopes’ colleague Bassanezi says the disease was probably in Brazil at least six years before symptoms were observed in 2004, and it was able to spread quickly as growers were not aware of it.

“We needed to train our growers to find the disease as soon as possible. As the disease spread in Sao Paulo other states became infected, like Minas Gerais and in the north and north-west of Paraná,” he says.

Fundecitrus researcher Renato Bazzanezi

“In April 2008 we had 0.6% of trees showing symptoms in the fields and in July 2010, 1.9% of trees showing symptoms in the field. You can see the disease is increasing.”

Brazilian authorities and growers have been fighting the disease on many fronts and have developed a series of recommended management strategies.

“If all the growers are involved within the process of HLB control, including government action, Fundecitrus, the growers, we can make production stable – we would lose 2% of actual production but we can have sustainability,” says Bassanezi.

“If the situation keeps as we are seeing now in the field, with only 35% of the trees under management, in 10 years we can have a reduction of 36%.”

Protection measures

Bassanezi highlights protected nursery production as a positive factor helping growers, while inspection procedures and tree elimination rules have also assisted containment.

“We have a state law that all nurseries must be at least more than 20 meters from any other citrus groves, and they use aphid-proof screens. Over the top we have a plastic screen, as we are also fighting against citrus canker and black spot,” he says.

“We are following Federal Law 53, which means all citrus growers need to have at least four inspections per year in their groves - elimination of the trees is paid by the grower and not by the government, and growers have to give at least two reports per year.

He says inspections involve PCR (Polymerase chain reaction) tests, whereby if 28% of groves are found to be positive they all must be eliminated.

“The disease has a late incubation period of six months to 1.5 years, so that means when you have 28% of symptomatic trees in the grove, this grower probably has 100% trees infected already.”

Photo: Apsnet

Figures until December 2010 show 9.7 million trees have been eliminated as a result of the scheme, while if you take into account unreported elimination and the recent half year the total number would surpass 10 million.

Bassanezi says growers have collected the insects using visuals in the shoots, while also using pesticides and yellow sticky traps.

Brazilian studies have shown the recommended management strategies are effective for large farms, but smaller growers surrounded by HLB-infected farms don’t stand much chance.

“If you have groves with HLB management, regular inspection of trees and regular control of the vectors, but these groves are small, the disease isn’t controlled even if you’re doing your job.

“If you are doing your job and you are surrounded by HLB, and your groves are large (100,000+) trees or have adult trees, you can deal with the disease. You can keep the disease at a good level of 1% or 2% per year, or you can also decrease the disease incidence.

“The problem is that in Brazil, for most growers the groves are smaller than 100,000 trees. That’s a very difficult thing to change, it’s a social problem. And if you look in our case, 60% of the trees in Sao Paulo state are located in small and medium-sized groves.

“So we need to help these small farmers, these small growers to do their job, because alone they couldn’t survive.”

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