For the first time, scientists have been able to measure the speed of the Candidatus Liberibacter asiaticus (CLas) bacteria that causes HLB disease. CLas are injected into citrus trees by psyllids feeding on the trees’ sap. CLas relies on this sap to grow and spread throughout trees.
Using a new statistical modeling analysis and measurement approach, plant pathologists were able to follow the bacterium on its journey through a tree. “We found that CLas can move at an average speed of 2.9 to 3.8 centimeters per day,” said Silvio A. Lopes, a plant pathologist based at São Paulo State University in Brazil. “At these speeds, a tree that is 3 meters in height will be fully colonized by CLas in around 80 to 100 days. This is faster than the symptoms appear, which generally takes at least four months.”
In other words, by the time growers see the symptoms of HLB, the tree has already been infected from the roots on up, which explains why removing symptomatic branches isn’t enough to cure a diseased tree.
Lopes and colleagues also studied the impact of temperature on the speed of colonization. They already knew that CLas does not multiply well in hot or cold environments, but now they have more specific numbers.
“We estimated that 25.7°C (78°F) was the best condition for CLas to move from one side to the other side of the tree,” said Lopes. This is the first time impact of temperature on plant colonization of CLas has been experimentally demonstrated. “The grower can use this information to select areas less risky for planting citrus trees,” Lopes said.
HLB was first reported in São Paulo in Brazil in 2004, a year earlier than it was discovered in Florida. Learn how Brazilians have used an integrated approach to manage HLB.
Source: American Phytopathological Society
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